• TABLE OF CONTENTS
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 Title Page
 Acknowledgement
 Table of Contents
 List of Tables
 List of Figures
 Introduction
 Results and discussion
 Experimental
 Summary
 List of References
 Biographical sketch
 Copyright














Title: Generation and reactions of 2, 2-diphenyldiazocyclopropane.
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Title: Generation and reactions of 2, 2-diphenyldiazocyclopropane.
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Table of Contents
    Title Page
        Page i
    Acknowledgement
        Page ii
    Table of Contents
        Page iii
    List of Tables
        Page iv
    List of Figures
        Page v
    Introduction
        Page 1
        Page 2
        Page 3
    Results and discussion
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
    Experimental
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
    Summary
        Page 34
        Page 35
    List of References
        Page 36
        Page 37
        Page 38
    Biographical sketch
        Page 39
        Page 40
    Copyright
        Copyright
Full Text











GENERATION AND REACTIONS OF

2,2-DIPHENYLDIAZOCYCLOPROPANE












By
MICHAEL HOWARD GRASLEY


A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF
THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY











UNIVERSITY OF FLORIDA
August, 1963














ACKNOWLEDGMENTS


To merely acknowledge the technical assistance of Dr. W. M.

Jones, the director of this research, would be too cursory. During

the tenure of this study he has been an unending source of inspiration,

understanding and friendship. His being more than just a research

director has given me more than just an education in organic chemistry

during my stay at the University of Florida.

The National Science Foundation is also to be acknowledged for

providing financial assistance.














TABLE OF CONTENTS

Page

ACKNOWLEDGMENTS. . . . . . . . . . . . i

LIST OF TABLES . . . . . . .. . .. . . . iv

LIST OF FIGURES. . .. . . . . . . .. . . . v

Section

I. INTRODUCTION . . . . . . . . . . . 1

IX. RESULTS AD DISCUSSION . . . . . . . . . 4

III EXPERIMENTAL . . . .. . . . . . . . . 24

IV. SUMMARY. . . . . . . . . . . . . . 34

LIST OF REFERENCES . . . . . . . . . . . . 36

BIOGRAPHICAL SKETCH. . . . . . . . . . . . . 39














LIST OF TABLES


Table Page

1. N. M. R. Chemical Shifts of Spiropentanes. . .. . . 8

2, Results of the Reaction of N-Nitroso-H-(2,2-Diphenyl-
cyclopropyl)urea with Lithium Ethoxide in Varying
trans-2-Butene Concentrations.- . .. . . . 13

3. Relative Rates of Addition of 2,2-Diphenylcyclo-
propylidene and Chlorocarbene to Olefins . .. . . . 18

4. The Properties of 2,2-Diphenylcyclopropylidene Adducts . 28














LIST OF FIGURES

Figure Page

1. Plot of Spiropentane/Allene Versus trans-2-Butene
Concentration . . . . . . . . . .. 14













1. INTRODUCTION


The chemistry of carbenes (derivatives of methylene, CH2) has

undergone a revival during the last ten years. Interest, research and

literature in this area of organic chemistry has grown in the light of

refined technology and theory to yield new methods of preparation and

reactions for these reactive intermediates as well as new and in-

triguing examples of carbene-containing systems. Among the newest of

systems is the particularly unusual cyclopropylidene. This small ring

carbene has inherently interesting features, and it is these same

features which have made it difficult to realize.

A divalent carbon in a three-membered ring has the possibility

of an intramolecular ring opening reaction besides the normal inter-

molecular carbene reactions. It is suggested that the intramolecular

reaction path contributes to the lack of success in cyclopropylidene

generation and capture. An allene, the result of ring opening, then

has been the predominant product in the many unsuccessful attempts to

capture cyclopropylidene.1'2'3'405s6o7 For example, Moore and Ward2

first reported that the reaction of 101-dibromocyclopropanes with

methyl- or butyllithium in cyclohexene gives allenes but none of the

spiropentanes that would result from addition of the anticipated8

cyclopropylidene to the carbon-carbon double bond. Similar failures

to trap this intermediate have also been reported by Logan4 who

examined the reaction of l1l-dichloro-2-alkylcyclopropanes with

magnesium metal in the presence of alkyl or aryl halides and by









Skattebol3 who studied the reaction of a variety of dihalocyclopropanes

with alkyllithiums. Again, both of these investigators found the

predominant products to be allenes.

Allene formation in reactions of this type is certainly not

unexpected for, even in 1958, Doering and LaFlammel reported that the

reaction of dibromocyclopropanes with magnesium or sodium yielded

allenes as the predominant products. Furthermore, Doering and LaFlaimne

suggested a variety of possible intermediates from which allene forma-

tion might occur in these reactions and convincingly narrowed the

possibilities down to collapse of either the bromocarbanion or the

carbene. However, they were not able to assess the relative importance

of these two modes of reaction since the presence of cyclopropylidene

could not be established. The problem of preventing the collapse to












> CHlCCCH2


allene of either the halo carbanion or the cyclopropylidene was very

cleverly solved by Moore and Ward2 who examined the reaction of 7,7-

dibromonorcarane with methyllithium. In this system, the cyclopropane

is fused to a six-membered ring which would certainly inhibit forma-

tion of the allene (1,2-cycloheptadiene) and, indeed, Moore and Ward

have isolated a variety of products which are typical of carbene









intermediates. For example, reaction with isobutylene gave spiro-

pentane X.


Br CH3
+ CH3Li + C=CH2

CH3





CH3



I


Recently, Skattebol7 reported another example of spiropentane

formation from reaction of 1,ldibromo-2-(but-3-enyl) cyclopropane

with alkyllithium reagents, which represents the third instance that

reaction products have suggested a cyclopropylidene intermediate. The

first case of such an instance is the subject of this work.

This approach to a cyclopropylidene uses the established

knowledge that diazo compounds are precursors to carbenes and also that

N-nitroso-N-alkylureas are precursors to diazo compounds. The objective

is then to obtain an N-nitroso-N-cyclopropylurea and from it generate
a diazocyclopropane which could lead to a cyclopropylidene. Both of

these reactive intermediates warrant characterization,













II. RESULTS AND DISCUSSION


As a starting point for synthesis of an N-nitroso-N-cyclo-

propylurea it was noted that 2,2-diphenylcyclopropane carboxylic acid

was readily obtained from the reaction of diphenyldiazomethane with

methyl acrylate.9 Conversion of this acid to the corresponding

nitrosourea was cleanly effected by the reaction shown in the flov

sheet.

0

CO2H .. SO2 C3 A
R- 2) aN3R -
R R



H 0 N=O0

N=C=O I N-02 -C-N

R- R- R
R R R

II

R = C6H5


The nitrosourea was then treated with a variety of bases in

attempts to generate 2,2-diphenyldiazocyclopropane. However, under all

conditions where any reaction occurred, spontaneous nitrogen evolution

was observed and, except for transient yellow colors, in no case was









a solution obtained that had the typical color of a 4iazoalkane. When

the reaction was effected in saturated hydrocarbon solvents, it was

found that the principal product was 1,1-diphenylallene (as high as

96 per cent yield but usually about 90 per cent). This result corre-

sponds to that of Schechter10 who reported that unsubstituted diazo-

cyclopropane undergoes decomposition to allene.

From these preliminary observations it was recognized that the

diazocyclopropane was probably being formed but was apparently quite

unstable, collapsing either in a concerted manner or via the carbene

to the allene4

N=O

IIc-tN2 Li002 5 G 2
II
R-> 0 R R_
R R
II


S C==C=-=CcH2
R
R C6H ,I

The nitrosourea was therefore treated with base in the presence

of acceptor olefins (usually as the solvent) and found to gives in

addition to appreciable quantities of the allene, the spiropentane
products anticipated from reaction of the carbene with the double bond.

Although many different bases have been found to be effective in this

reaction, it was found that by far the cleanest product results from

the reaction of the nitrosourea with unsublimed, air-dried lithium

ethoxide (a white powder that contains about one mole of what is

probably ethanol). In a typical reaction, the nitrosourea was stirred








CH3


II + LiOC2H5 + C=CH2 + IV


C6A5

III


with an equimolar amount of lithium ethoxide (alcoholate) in isobutylene

until nitrogen evolution ceased (generally about 90 per cent of

theoretical), Elution chromatography of the hydrocarbon soluble product

gave 18 per cent of the spiropentane III G.l.p.c, analysis of the

crude reaction product showed 22 per cent of the spiropentane to be

present. The generality of this reaction for the synthesis of hydro-

carbon spiropentanes was shown by effecting the reaction in the presence

of a variety of acceptor olefins (see Table 4 in the Experimental

Section). In each case, the other major product was 1,1-diphenylallene.

Generally, the total yield of hydrocarbon products was 85-90 per cent.

The spiropentane structures were initially c zggested for the

adducts as a result of analyses, molecular weights (on the adducts

arising from reaction with cis* and trans-2-butene), negative chemical

tests for unsaturation and the fact that the ultraviolet spectra of all

adducts were found to be virtually identical with the spectra of typical

diphenylcyclopropane model compounds. In addition to the above men-

tioned tests, the following spectral and chemical data present com-

pelling evidence for the spiropentane structures.

Infrared spectra.--The infrared spectra of all adducts show no

absorption between 5.8 and 6.5p except for the typical phcnyl absorption

which appears around 6,311. Furthermore, all adducts show a moderately









strong, sharp absorption at 9.88 O0.03p. The significance of this

absorption deserves some attention. Contrary to earlier reports1

recent evidence has appeared which suggests that there is not a truly

reliable characteristic infrared absorption in the ten micron region

for the cyclopropane ring.12 However, Wilcox and Craig13 have very

recently reported their observation that several 7-spirocyclopropane

derivatives of 2,2.1 bicyclic systems all show a band at 9.91 + 0.03p,

an absorption that they feel is quite characteristic of this type of

compound, The fact that the spirocyclopropanes of Wilcox and Craig13

experience exocyclic strain similar to the cyclopropane rings of

spiropentanes suggest the possibility that the absorption at 9.91p

might be generally characteristic of strained cyclopropane rings.

The near infrared spectra of some of the spiropentanes were

also examined. It was found that, as would be expected for cyclopro-

pane rings,14 in every case examined an absorption was found at about

1.65p.

Nuclear magnetic resonance spectra.--The nuclear magnetic

resonance spectra* bear out the assignment of spiropentane structures

to the hydrocarbon products. The chemical shifts of several represen-

tative spiropentanes are described in Table 1. These shifts in con-

junction with an analysis of the coupling constants for the ring

hydrogens involved, clearly suggest the presence of two cyclopropane

rings in these hydrocarbon products. These data are particularly con-

vincing in their agreement with literature values for



"For a detailed discussion see W. M. Jones, M. H. Grasley and
W. S. Brey, Jr., J. Am. Chem. Soc., 85* in press.














Table 1

N. M. R. Chemical Shiftsa of Spiropentanes

Chemical Shifts (r Values)
H on Ring
H on Ring Derived
Bearing from Methyl
Acceptor Olefin Phenyl Phenyls Olefin Hydrogens


trans-2-Butene 2.84b 8.55 c c
3.01b 8.63

Isobutylene 2.75 (sharp) 8.48 9.31 8.74
doublett)
3.0 (broad) 9.54 9.00
doublett)

cis-2-Butene 2.89 (sharp) 8.63 9.0 8.97
multiplee)

2,3-Dimethyl-2*
butene 2.91 (sharp) 8.52 -- 8.90
9.07

Cyclohexcne 2.90 (broad) 8.56 8.65d -
2.94 (broad)


aTau values from tetramethylsilane.
bBroadens on dilution.

COverlapping rultiplet.
dBroad band, 8.0 to 9.5.








chlorospiropentanel5 and disagreement with values for several cyclo-

butanes.16 17

Alternate synthesis.--Finally, as quite compelling evidence for

the structure of at least one of the products, the adduct isolated from

the reaction of-the nitrosourea with base in the presence of cyclo-

hoxene was alternately synthesized by the method of Moore and Ward.2

The two products had identical melting points, showed no depression


Li2OC2H


R
+ C=CH2
R


n-Butyl-
lithium


R = C6%5


upon admixture, had identical g.l.p.c. retention times and identical
infrared spectra.

Nature of the intermediate.-**Even though adducts with spiro-

pentane structures are being formed, it is not unequivocal evidence








for the formation of a cyclopropylidene. There are, however, several

factors which certainly suggest the intermediacy of the carbene,

Initially, it should be pointed out that the formation of

1,1-diphenylallene from the action of lithium ethoxide on N-nitrosow

N-(2,2-diphenylcyclopropyl)urea results from at least two distinct

precursors.18 Only one of these precursors is capable of reaction with

an olefin to give a spiropentane. These conclusions were drawn in the

following manner.

Consider the following reaction scheme, For the sake of clarity


Nitrosourea (II)
Sk 2-Butene Spiro-
+ k4"2 k pentane
R- R-
Lithium Ethoxide V
R R

k3



k 2 R CC
> C==-C==-CH

R

R = 06H5

the diazocyclopropane and the carbene are assumed to be distinct inter-

mediates. However, it must be pointed out that the diazocyclopropane

has never been isolated and no proof of a free carbene has been pre-

sented., Thus, these results could be equally well accommodated by a

concerted decomposition of the nitrosourea or the diazocyclopropane (or

both) combined with reaction of the carbene with the olefin; or, even

possibly a concerted decomposition of the nitrosourea followed by direct









reaction of the diazocyclopropane with olefin to give the spiropentane.

However, whatever the actual nature of the distinct intermediates, the

results reported are most readily accommodated by a scheme involving

two different intermediates; only one of which is capable of reacting

with olefin to give a spiropentane.

Employing a steady state treatment and assuming the butene con-

centration does not change appreciably during the reaction, it can be

shown that the ratio of spiropentane to allene can be expressed by the

general equation (1).

Spiropentane kk4 (Butene)
Allene k1k3 + k2k3 + k2k4 (Butene)


If the sole source of allene is cyclopropylidene (V) (.,e.,

k2 0) then equation (1) reduces to (2) and a plot of the ratio of

Spiropentane k4 (Butene) (2)
Allene k3


spiropentane to allene versus the concentration of butene should give

a straight line with slope k4/k3.

On the other hand, if the sole source of allene is a concerted

decomposition of the diazocyclopropane ( k.., k3 = 0) then equation (1)

reduces to (3) and it is seen that the ratio of spiropentane to allene

would be independent of the concentration of the olefin.

Spiropentane -- (3)
Allene k2


Finally, of course, if k2 and k3 are competitive and the allene

has two distinct precursors (pictured here as the diazocyclopropane and









the cyclopropylidene), then the ratio of spiropentane to allene should

be expressed by equation (1).

Analytical techniques were therefore developed for determining

absolute concentrations of 1,1-diphenylallene and the spiropentane

which has been found5 to result from the addition of 2,2-diphenyl-

cyclopropylidene to trans-2-butene.* The results of a series of

reactions of the nitrosourea with lithium ethoxide at varying concen-

trations of trans-2-butene are shown in Table 2. It is at once seen

that the ratio of spiropentane to allene is not constant; thus excluding

a concerted decomposition of the diazocyclopropane as the sole source

of allene. Further, a plot of the ratio of spiropentane to allene

versus the concentration of butene is shown in Figure 1. These points

obviously do not give a straight line. Thus the carbene as the sole

precursor of the allene becomes an unlikely possibility.

Finally, it was found that the experimental observations could

be quite well accommodated by equation (1) which is conveniently

simplified to (4) by dividing the numerator and the denominator by

k2k4. Values of 0.52 for kl/k2 and 3.06 for k3/k4 were then obtained

k1
(Butene)
Spiropentane k2 (Bute
Allene klk3 + k3 + (Butene)
k2k4 k4


*Gas chromatography was used to determine the concentration of
the spiropentane. Methyl-alpha-methyl cinnamate was used as an internal
standard. The tendency of 1,1-diphenylallene to polymerize3 under even
very mild thermal conditions made gas chromatography an unreliable
analytical tool for determining its concentration. However, it was found
that the ultraviolet absorption of the allene at 250 millimicrons could
be used quite successfully since the allene appears to be stable at low
temperatures and low concentrations.

















Table 2

Results of the Reaction of N-Nitroso-iN-(2,2-Diphenylcyclopropyl)urea
with Lithium Ethoxide in Varying trans-2-Butene Concentrations

Spiropentane
t-2-Butene, aoles/liter Allene


1.14 0.113

1.14 0.103

1.14 0.098

2.27 0.157

2.27 0.168

3.41 0*236

4.51 0.268

6.81 0.339

6.81 0.286

7.95 0.318

11.35 0.362

11.35 0.362






















































0.2 0.3
Spiropentane / Allene


0.4


Plot of Spiropentane/Allene Versus trans-2-
Butene Concentration

(Curve calculated from equation (4) (solid
line): 0, experimental results.)


r+J


C
o
U
c-
0_


Figure 1.









from the slope and an intercept of a least squares plot of spiropen-

tane/(allene)(butene) versus spiropentane/allene. When these values

were substituted into equation (4) the calculated curve shown in

Figure I was obtained. Thus, although the observed curvature might

possibly result from a reaction mechanism not considered or, even

possibly, from solvent effects, the coincidence of the curve calculated

from equation (1) and the observed curve is quite striking and certainly

suggests that the allene does indeed have two different precursors,

As noted previously, this treatment does not present evidence

for the precise nature of the allene precursors and although the diazo-

cyclopropane and carbene are intuitively attractive intermediates, the

data presented could conceivably be explained by other pairs of possible

allene precursors. Of the possible candidates for these two species,

there are at least two that should be considered as spiropentane pre-

cursors: the carbene and the diazocyclopropane. That the latter com-

pound is an unlikely possibility is apparent for several reasons. First,

the reaction of diazoalkanes with olefins unactivated by electron with-

drawing groups is rare and generally involves strained double bonds.19

Furthermore, in those cases where reaction with non-activated double

bonds has been observed, the pyrazoline has been isolated as a stable

product. For instance, the 1-pyrazoline that would be formed by reaction

of the diazocyclopropane with an unactivated double bond would be

expected to be quite stable since it would simply be an unactivated

five-membered azo ring. For comparison, azo-isopropane (i-Pr-NH=N-jIPr)

is an extrenaly table material exhibiting an activation energy of

41 Kcal. per mole for its decomposition*20









The other possible method by which the diazocyclopropane could

react directly with the double bond to give a spiropentane would involve

formation of some type of 1-pyrazoline precursor (possibly a zwitterion)

which could lose nitrogen before ring closure. Such an explanation is

unattractive and has no known precedent.

Finally, by far the most convincing evidence for the two

allene precursors being the diazocyclopropane and the carbene arises

from the reaction of the nitrosourea with lithium ethoxide in the

presence of diethyl fumarate. Of initial significance was the fact that,

in the presence of diethyl fumarate, there was no detectable nitrogen

evolution and 1,1-diphenylallene was formed in only trace amounts.

This leads to the conclusion that the diethyl fumarate must interrupt

the reaction prior to formation of the second allene precursor. Further-

more, from the product ratio studies previously reported, it is known

that the ratio of k1/k2 in equation (1) is about 0.5. In other words,

only about one-third of the initial allene precursor goes to the second

allene precursor. However, there was isolated from the reaction in the

presence of diethyl fumarate a 47.5 per cent yield of the pyrazoline

that would be expected from reaction of the diazocyclopropane with the

ester. It therefore becomes obvious that the first allene precursor

must be a nucleophilic species and, furthermore, must be capable of

giving the pyrazoline with diethyl fumarate, In other words, the

C2 502c

II + Diethyl Fumarate LiOC2H 1 1


C6H5









diazocyclopropane is the most likely first allene precursor. This,

then, leaves the cyclopropane as the most likely candidate for the

second allene precursor and the intermediate that reacts with olefins

to give spiropentanes.

More direct evidence for the carbene as a distinct intermediate

was obtained by competitive reactions with various olefins. This is a

test that has been applied in many instances to determine the electro-

philicity or nucleophilicity of carbenes. In most instances, the

carbene behaves as an electrophile, thus leading to the prediction

that the more nucleophilic the double bond, the faster the reaction.21

The results of our investigation are summarized in Table 3 and are com-

pared with a comparable study of an unsymmetrical carbene, the chloro-

carbene.22

The data do not follow the order that would be predicted by

strictly electronic considerations for either an electrophilic or a

nucleophilic species. However, they do follow the order predicted for

an unsymmetrical electrophilic species that exhibits a dominating steric

effect* when the two phenyl rings on the cyclopropylidene are opposed to

one or more alkyl groups. For example, addition to isobutylene occurs

more rapidly than addition to trans-2-butene. In each of these cases,

one of the incoming phenyl rings is opposed to one methyl group and the

predicted electronic order obtains. On the other hand, addition to

isobutylene is faster than to 2,3-dimethyl-2-butene. In the latter




*There are instances in the literature which show that steric
effects for unsymmetrical carbenes may23 or may not24 be operative.
However, the non-operative cases are rare and 2,2-diphenylcyclopropyl-
idene is unique with regard to its overwhelming steric requirements.








Table 3
Relative Rates of Addition of 2,2-Diphenylcyclopropylidene and
Chlorocarbene to 0lefins

Olefin (k/ko) cyclopropylidene' (k/ko)CICE

2,3-Dimethyl-2*butene 0.41 2.80

Isobutylene 1.00 1.00
trans-2-Butene 0.42 0.45
cis-2-Butene 1.15 0.93

Cyclohexene 1.23 0.60
1-Pentene 0.23
1-Butene 0.22


aMeasured in competition with cyclohexene.

bThese data are taken from Close and Schwartz.22






C6H, V r


lC6


VR
R

R


5 6U
R


R


-









case, both of the phenyl rings are opposed to alkyl groups and the

steric effect prevails.* Cyclohexene and cis-2-butene were found to

be particularly reactive, a result that would be predicted for a

reaction in which the two phenyl rings of the cyclopropylidene can

approach unopposed to any alkyl groups.+ Finally, 1-butene was found

to be the least reactive of all the olefins studied even though the

two phenyls could approach unopposed to any alkyl groups. This again,

suggests that the intermediate is an electrophilic species.

Another common characteristic of carbenes is their tendency to

insert into carbon-hydrogen bonds.26 Products resulting from the

insertion of the cyclopropylidene were therefore sought. Such products

were not detected when the nitrosourea was treated with base in hydro-

carbon solvents. Attempts to isolate insertion products from reaction

of the nitrosourea with base in the more reactive diethyl ether27 have

failed. However# the gas chromatogram of the crude reaction mixture

shows several new peaks with retention times that are consistent with

insertion products.

Since the intermediate in the reaction of the nitrosourea with

base is apparently the carbene, it was thought interesting to apply

Skell's28 chemical test for the multiplicity of the electrons. Reaction



*Vbore, Ward and MNrritt25 have reported that the cyclo-
propylidene derived from 7,7-dibromonorcarane does not add to 2,3-
dimethyl-2-butene and have attributed this to steric hindrance.

+Reaction with cyclohexene and cis-2-butene could give products
in which the two phenyl rings are either cis or &rans to the alkyl
portion of the original olefins. In both cases, only one product could
be isolated and the gas chromatogram of the crude reaction mixtures
showed single spiropentane peaks. It is most likely that both isomers
were formed but not separated on our column.









of the cyclopropylidene was therefore effected with cis- and trans-2-

butene and, within experimental error the reaction was stereospecific.*

This suggests that insofar as Skell's chemical test for the multipli-

city of electrons is general, at the instant of reaction with the olefin

the cyclopropylidene is in the singlet form. This is consistent with

the observation of boore, Ward and Merritt,25 that the reaction of 7,7-

dibromonorcarane with alkyllithium in the presence of cis- and trans-

2-butene is stereospecific.

The apparent extreme thermal instability of the diazocyclo-

propane deserves some mention. In contrast to most simple diazoalkanes

(including diazocyclobutane)29 diazocyclopropane decomposes spon

taneously even at temperatures as low as -200. One obvious reason for

this rapid loss of nitrogen is the concerted collapse of the diazo-

cyclopropane to the allene. However, the loss of nitrogen from the

ring to give the carbene must also be quite rapid to compete with the

concerted decomposition to the allene. As a possible explanation for

this reactivity it is likely that ring strain holds the nitrogen of

the diazocyclopropane out of the plane of the ring. This, in turn,

decreases the double bond character of the carbon-nitrogen bond by

effectively reducing the contribution of canonical form VI to the



*The product from the reaction of the carbene with trans-2-
butene was devoid of any of the cis-2-butene product. However, the
product from the reaction with cis-2-butene showed a small shoulder on
the cis-adduct g.l.p.c. peak (less than 10 per cent) with a retention
time the same as the trans-adduct. This was at first disturbing. How-
ever, chromatographic analysis of the cis-2-butene (Natheson, C. P.
grade) used for the experiments showed two peaks, the smaller of which
had the same retention time as trans-2-butene. Accurate determination
of the amount of this material was not possible, but it appeared to be
on the order of 15 per cent of the mixture.









diazocyclopropane hybrid, which results in an effective lowering of the

activation energy for loss of the nitrogen.






C6H5 NN C6H


VI

During the course of this investigation it was noticed that

N-nitroso-N-(2,2-diphenylcyclopropyl)urea (II) thermally decomposed

(as low as 600 in solution and 114 in the melt), evolved a gas and

produced almost quantitative amounts of 1,1-diphenylallene, In fact,

this thermal decomposition was used as a preparative method for 1,1-

diphenylallene, The intermediates which form this allene under thermal

conditions were indeed interesting in view of the work just discussed

on base decomposition of the same nitrosourea.

If thermal decomposition provides the same intermediates to

allene formation as the base decomposition, then it would represent a

new synthetic method of cyclopropylidene generation. The new method

would have the advantages of being a cleaners strong-base-free reaction,

thereby allowing easier product isolation and cyclopropylidene genera-

tion in the presence of base sensitive systems.

Information about the nature of the intermediates in the thermal

decomposition of the nitrosourea (II) was obtained from a comparison of

the decomposition in the presence and absence of an acceptor olefin.

In 100 per cent n-heptane decomposition led to 95 per cent 1,1-diphenyl-

allene whereas in 100 per cent cyclohexene decomposition led to 65 per









cent 1,1-diphenylallene and 22 per cent of spiropentane (VII),* It is

therefore apparent that the spiropentane precursor must also be capable



N=O

C61 CN2 reflux C615



II VII

+ (C6H5) 2C=C=CH2


of decomposing to the allene. The previously discussed studies on the

base decomposition of nitrosourea (II) have clearly demonstrated that

2,2-diphenylcyclopropylidene is a spiropentane precursor capable of

producing an allene, Therefore a cyclopropylidene, produced thermally

from (II), is reasonable.

A cyclopropyl radical is-an interesting possibility as a spiro-

pentane precursor, but has been excluded on the basis of its thermal

stability*30 Also there is the possibility of a cyclopropyl cation

as the precursor to the spiropentane; however, this unstable cation

collapses to an allylic cation31 and there is no case known where an

allylic cation yields an allene.

Additional support for the carbene intermediate can be found in

the rather extensive studies of the thermal decompositions of a variety

of nitrosoamides; compounds .that are certainly closely related to the



*The spiropentane (VII) was identical in every way with the
product synthesized from the reaction of nitrosourea (II) with lithium
ethoxide in cyclohexene at 0.









nitrosourea under consideration. It has been found that such decom-

positions proceed to products by way of either the alkyl diazonium

ion or the diazoalkane. In particular, systems that could lead to

relatively stable cations are believed to proceed through the alkyl

diazonium cation (e.g., secondary carbinamine derivatives).32 In

contrast, N-nitrosoamide derivatives which could lead to unstable

cationc33 (specifically, amides of primary carbinamines) have been

shown to proceed through the corresponding diazoalkanes.33'34

If it is assumed that the mechanism of the thermal decomposition

of the cyclopropyl nitrosourea (II) is analogous to the mechanism of the

thermal decomposition of nitrosoamides, then the instability of the

cyclopropyl cation would predict that the decomposition would follow

the diazoalkane route. Furthermore, the apparent instability of 2,2-

diphenyldiazocyclopropane would predict immediate loss of nitrogen to

give the cyclopropylidene.

If these predictions are correct, thermal decomposition of the

nitrosourea (II) in diethyl fumarate should parallel the base decom-

position and yield the trapped 2,2-diphenyldiazocyclopropane in the

form of a pyrazoline. Such was found to be the case,

N=0 C02C2115

+N1-C-FH2 Diethyl 80oC 02C2I-5
H5C6 Fumarate

C6H C6H5 H



The analogy between the base and thermal decomposition of the

nitrosourea (II) is complete. Both yield a diazocyclopropane and a

cyclopropylidene, which were the object of this study,













III. EXPERIMENTAL*


Materials.--Cyclohexene (Eastman Kodak White Label) was

purified by fractional distillation before use. Isobutylene, trans-2*

butene, cis-2-butene and 1-butene (all Matheson, C. P. grade) were

used without further purification. n-Heptane (Phillips Hydrocarbons,

research grade) was used without further purification as was 2,3-

dimethyl-2-butene which was obtained from K & K Laboratories. n-Butyl-

lithium in hexane was used as obtained from the Foote Mineral Company.

Analyses for spiropentanes and ll-diphenylallene.--G. l,p.c.

analyses were carried out at 2500 using an Aerograph A-350 vapor

fractometer containing a ten foot 1/4 inch column charged with G. E.

SF-96(50) silicone fluid on 60-100 mesh firebrick.

Absolute amounts of the various spiropentanes were determined

by employing an internal standard (alpha-methyl methylcinnamate). Due

to the tendency of 1l1-diphenylallene to polymerize, g.l.p.c. could not

be used for its analysis. The ultraviolet absorption of the allene at

250 millimicrons (6 = 12,030) was used to determine its concentration.

N- (2,2-Diphenylcyclopropyl)urea --In a typical preparation$

18 ml. (0.25 moles) of thionyl chloride was added to 30.0 g. (0.126

moles) of 2,2-diphenylcyclopropane carboxylic acid.9 The mixture was

refluxed for 2 hours after which all traces of thionyl chloride were

removed by distillation under reduced pressure. To the residual acid



*I4elting points are uncorrected.

24









chloride was added 250 ml. of dry acetone. The mixture was stirred

and cooled in an ice bath. To the cold solution was rapidly added

8.2 8. (0.126 moles) of sodium azide dissolved in a minimum amount of

water. The mixture was stirred with cooling for one hour after which

it was poured into water and extracted with ether. The ether layer.

was dried over magnesium sulfate (it is crucial that the ether layer

be quite dry). The dry ether solution of the acid azide was added

dropwise to 400 ml. of dry refluxing benzene. After the addition was

complete the benzene solution was refluxed until nitrogen evolution

ceased. The benzene solution was then cooled in an ice bath and

anhydrous ammonia passed through the cold solution for two hours, For

best results the ammonia should be passed into the solution quite

rapidly for the first fifteen minutes. The urea precipitated from the

cold benzene solution as a white solid. Recrystallization from a

mixture of ethanol and water gave 16 g. (overall yield of 50 per cent)

of the pure urea; m.p. 134-135.

Anal. Calcd. for Cl6Hl6N2O: C, 76.16; H, 6.39; N# 11.10.

Found: C, 75.98; H, 6.44; N, 11.07.

N*Nitroso-N- (2.2'diphenylcyclopropyl)urea.*--Sixteen g.

(0.0635 moles) of N-(2,2-diphenylcyclopropyl)urea was dissolved in 60 ml.

of a mixture of 70 per cent glacial acetic acid and 30 per cent acetic

anhydride. The mixture was cooled in an ice bath. To the cold,

stirred solution was added dropwise over a thirty minute period 4.42 g.

of sodium nitrite (0.064 moles) dissolved in 20 ml. of water. To this

solution was added 40 ml. of water. The nitrosourea precipitated from

the solution during the addition of the water. The precipitate was

removed by filtration and washed well with water followed by a little









ether. Recrystallization from a mixture of chloroform and petroleum

ether gave 9.0 g. (50 per cent) of a very light yellow solid, m.p. 1144-

1150 (dec.).

Anal. Calcd. for C16HS1N302 C, 68.31; H, 5.37; N, 14.94.

Found C, 68.42; H, 5.53; N, 14.88.

Lithium ethoxide.--To 100 ml. of absolute ethanol in a flask

equipped with an efficient condenser was added lithium wire (3.5 g.,

0.5 moles). After the initial reaction subsided, the mixture was

refluxed for eight hours. The excess ethanol was then removed by

evaporation under reduced pressure to give a white amorphous solid. Air

drying yielded a finely divided solid weighing about 42 g. This solid

is presumed to be lithium ctho::ide monoalcoholate since treatment with

sodium hydride evolved a volume of hydrogen consistent with such a

formulation. Removal of ethanol from the solid may be accomplished

using sublimation techniques. Attempted sublimation at 240 and 2 mm.

of Hg gave a small amount of sublimed material which had retained its

ethanol. However, the bulk of the material did not sublime but lost

its ethanol leaving behind a white solid which ignited upon exposure

to the atmosphere.

The preparation of lithium ethoxide as reported by Brown

Dickerhoof and Bafus35 was also used. However, the ethoxide so

obtained showed no advantages to that obtained by simply dissolving

lithium in ethanol.

Reaction of N-nitroso-UN- (22-diphenylcyclopropyl)urea with

lithium ethoxide in isobutylene.--To 1.0 g. (3.6 mmoles) of the nitroso-

urea in a flask equipped with a Dry Ice cold finder condenser was

added 25 ml. of isobutylene. The stirred mixture was cooled to -350









and 0.35 g. (3.6 mmoles assuming the material is the alcoholate) of

lithium ethoxide was added. The reaction mixture was vigorously

stirred and allowed to warm to -150 and maintained near this tempera-

ture throughout the reaction. Upon reaching -150 nitrogen evolution

began and continued for ca. 30 minutes to give a total of about 90 per

cent of the quantitative amount. Stirring and cooling were continued

for one additional hour after which the reaction mixture was filtered.

The residual solid was washed with reagent grade n-heptane and the

extracts combined with the filtrate. Aliquots of the filtrate were

analyzed for the spiropentane (22 per cent) by g.l.p.c. and for 1,1-

diphenylallene36 (65 per cent) by the ultraviolet. The remainder of

the filtrate was evaporated to a yellow oil from which the spiro-

pentane was isolated by chormatography on activated alumina (ca. 60 g.

of alumina per g. of mixture) using petroleum ether as the eluting

solvent. The spiropentane came off of the column very quickly followed

rather closely by the allene. Recrystallization of the spiropentane

from 95 per cent ethanol gave 0.16 g. (19 per cent) of white needles,

m.p. 47.5-48.0.

Anal. Calcd. for C19H20: C, 91.88; H, 8.12. Found C, 91.99;

H, 8.08. The results of similar experiments in the presence of a variety

of olefins are given in Table 4.

Nuclear magnetic resonance spectra.--The n.m.r. spectra were

run in solution in carbon tetrachloride, with tetramethylsilane as

internal reference, using a Varian DP-60 instrument. Chemical shifts

were determined by measurement of side-banded spectr-, '*sinr, the average

of repetitive scans and continuously monitoring the oscillator frequency

with an electronic counter. Values of the shifts were converted to









The Properties


Table 4

of 2,2-Diphenylcyclopropylidene Adducts


Near Anal.
Yield Retention Infrared Infrared Calcd. Found
Acceptor M.P. (g.l.p.c.) Timesc Absorption Absorption C H C H


2,3-Dimethyl-
2-butene 69.5-70.0a 16% 26.3 min. 9.88 1.648 91.25 8.75 91.25 8.90

Isobutylene 47.5-48.0a 227. 26.6 min. 9.86 1.648 91.88 8.12 91.99 8.08

trans-2-Butene 51.5-52.0a 23% 17.0 min. 9.86 1.648 91.88 8.12 92.05 7.91

cis-2-Butene 31.0-32.0a 22% 17.1 min.d 9.86 1.647 91.88 8.12 92.06 7*76

Cyclohexene 82.0-82.5b 21% 49 min. 9.91 1.654 91.92 8.08 91.84 8.06

1-Butene oil 9% 20.4 main. 9.84 91.88 8.12 91.60 8.33


aRecrystallized from
bRecrystallized from


95%7 ethanol.

ethyl acetate.


cFor g..lp.c. conditions, see "Analyses for spiropentanes and 1,1-diphenylallene" in the Experimental
Section.

dThe gas chromatogram of this reaction mixture showed a second peak at 20.1 rin. which is probably
due to the cis-isomer. This material occurred in such a small yield that no attempt was made to isolate
and characterize it.








those for infinite dilution by extrapolating the results obtained on

the original solution, usually a saturated solution, and on solutions

with concentrations of 50 per cent and 25 per cent of the concentration

of the original solution.

Competitive reactions with various olefins.--To a cooled (ice

bath) stirred mixture of 10 ml. each of cyclohexene and the competing

olefin containing 0.50 g. (0.0018 mole) of N-nitroso-N-(2,2-diphenyl-

cyclopropyl)urea was added 0.19 g. (ca. 0.0019 mole) of lithium ethoxide

alcoholate. Nitrogen evolution began immediately and was essentially

complete in 10 minutes. Stirring and cooling were continued for an

additional 30 minutes at which time the reaction mixture was filtered

and the filtrate evaporated to give an oily residue that was analyzed

by gol.p.c.

Alternate synthesis of 1,l-diphenyl-4,5-tetramethylenespiro-

pentane.-*7,7-Dibromonorcarane37 (14.0 g., 0.056 moles) and 10.0 g.

(0.056 moles) of 1,1-diphenylethylene38 were dissolved in 15 ml. of

dry ether and the mixture was cooled to 00. n-Butyllithium in hexane

(3.56 g,, 0.056 moles) was added dropwise to the stirred and cooled

mixture over a 45-minute period. After the addition was complete the

reaction mixture was stirred for an additional two hours at room

temperature and filtered. The filtrate was washed with water and

dried over magnesium sulfate. The dried solution was removed of

volatiles and a small portion (0.25 ml.) was separated by gas chroma-

tography to give about 10 Mg. of the desired spiropentane. Recrystal-

lization from ethyl acetate gave pure material, m.p. 82.0-82.50; no

depression on admixture with the material obtained from the reaction of









the nitrosourea with lithium ethoxide in cyclohexene. The infrared

spectra of the two materials were also identical.

Reaction of N-nitroso-N-(2.2-diphenylcyclopropyl)urea with

lithium ethoxide in n-heptane.--To a stirred mixture of the nitroso-

urea (1.00 g., 3.56 moles) in 25 ml. of reagent grade n-heptane at 0

was added lithium ethoxide alcoholate (0.35 g., ca., 3.6 moless. After

5 minutes stirring nitrogen evolution began and was 95 per cent com-

plete after 60 minutes. Stirring and cooling were continued for one

additional hour after which the reaction mixture was filtered. The

residue was washed thoroughly with reagent grade n-heptane and the

filtrates combined. The filtrate was analyzed for 1,1-diphenylallene

and found to contain 96 per cent of the calculated,

The allene is a colorless oil when it is first formed or

immediately after it is eluted from alumina (if it is kept cold).

However, it apparently polymerizes rather rapidly when it is kept'as

the liquid at room temperature.3 The structure of the allene was

deduced from its infrared spectrum36 and by partial reduction to a

product which was identical in every way with an authentic sample of

1,1-diphenyl-l-propene.

Reaction of N-nitroso-N-(2,2-diphenylcyclopropyl)urea with

lithium ethoxide in ethyl ether.--To 2.00 g. (0.0071 moles) of N-

nitroso-N-(2,2-diphenylcyclupropyl)urea and 25 ml. of pure anhydrous

ethyl ether stirred at 0 was added 0.70 g. (0.00715 mole) of lithium

ethoxide alcoholate. Nitrogen evolution began immediately and con-

tinued for approximately 40 minutes. After a total of two hours

stirring and cooling the reaction mixture was filtered; the solid

obtained was washed with anhydrous ethyl ether and the washing added to









the filtrate. Evaporation of the filtrate gave a yellow oil which was

chromatographed over alumina using pentane as the eluent. The oil

obtained by this chromatography was shown by g.l.p.c. to be a complex

mixture and at least three major components of this mixture are unique

to the reaction in ethyl ether; they are not produced by this reaction

when run in saturated hydrocarbon solvents. Attempted purification and

isolation of the various components by preparative scale g.l.p.c. was

not successful.

Decomposition of N-nitroso*N-(2,2-diphenylcyclopropyl)urea by

lithium ethoxide in diethyl fumarate.--To 1.00 g. (0.00356 mole) of N-

nitroso-N-(2,2-diphenylcyclopropyl)urea in 20 ml. of diethyl fumarate

(Eastman Organic Chemicals) at 00 was added 0.35 g. (0.0036 mole) of

lithium ethoxide alcoholate. The mixture was stirred and cooled for

one hour at the end of which no nitrogen had evolved and a white solid

had precipitated. Isolation of the solid by filtration was followed by

thorough washing with pentane. (The filtrate was shown by g.l.p.c. to

contain both benzophenone and a trace of 1,l-diphenylallene.) The

isolated solid was then stirred with cold, dilute hydrochloric acid,

filtered, washed with water and dried. Recrystallization from methanol

gave the pyrazoline in 47.5 per cent yield, m.p. 147-1490, )max 320 mp

(6 = 10,900), 3.001, 5.76p, 5.99p, 6.52p.

Anal. Calcd. for C23H24N204: C, 70.39; H, 6.16; N, 7.14.

Found: C, 70.20; H, 6.30; N, 6.88.

Decomposition of N-nitroso-N-(2,2-diphenylcyclopropyl)urea by

lithium ethoxide in varying concentrations of trans-2-butene.--A series

of reactions were run using 1.00 S. (3.56 moles) of N-nitroso-N-(2,2-

diphenylcyclopropyl)urea and 0.35 g. of lithium ethoxide (alcoholate) in









a total of 25.0 ml. of varying molar concentrations of trans_-2-butene

and n-heptane at 0. The nitrosourea and a known amount of n-heptane

were mixed and cooled to 0o, then the appropriate amount of trans-2-

butene was condensed into the mixture by means of a Dry Ice cold finger.

Next the lithium ethoxide (alcoholate) was added and N2 evolution began.

Stirring and cooling was continued for a total of forty-five minutes

after which the reaction mixture was filtered. The residual solid was

washed with n-heptane and the extracts combined with the filtrate,

Aliquots of the filtrate were then analyzed for the spiropentane

(g.l.p.c.) and for 1,1-diphenylallene. For the results of a series of

analyses see Table 2.

Thermal decomposition of N-nitroso-N-(2,2-diphenylcyclopropyl)-

urea in n-heptane.--A stirred mixture of 1.00 g. (3.56 mmoles) of N-

nitrosoN--(2,2-diphenylcyclopropyl)urean and 25 ml. of n-heptane was

heated to 800 and held for thirty minutes. During the heating, gas

evolution began around 600 and continued for twenty minutes at which

time at least a quantitative amount had evolved. Gas evolution in this

reaction is consistently greater than one mole per mole of nitrosourea.

Presumably this is a result of other gases than nitrogen being produced

by the urea portion of the molecule. After the thirty-minute period the

reaction mixture was cooled to room temperature and diluted with n-

heptane for 1,1-diphonylallene analysis. Analysis by means of its

ultraviolet absorption at 250 my (C = 12>030) showed a yield of 95 per

cent.

Thermal decomposition of N-nitroso-IU-(22-diphenylcycloprog l)-

urea in cyclohexene.--A stirred mixture of 1.00 g. (3.56 moles) of N-

nitroso-N-(2,2-diphenylcyclopropyl)urea and 25 ml. of cyclohc::eno was









brought to reflux and held for thirty minutes. At the end of this

period gas evolution had ceased and the yellow solution had lost its

color. After cooling to room temperature aliquots of the mixture were

analyzed for the spiropentane (by g.l.p,c. using Alpha-methyl methyl-

cinnamate as an internal standard) and 1,1-diphenylallene (by its

ultraviolet absorption at 250 ma, EC 12,030). The yield of spiro-

pentane was 21.9 per cent and the yield of 1,1-diphenylallene was 65 per

cent.

Thermal decomposition of l-nitroso-N-(2,2-diphenylcyclopropyl)*

urea in diothyl fumarate.--To 25 Ma. of diethyl fumarate (Eastman Organic

Chemicals) was added 3.00 g. (0.0107 mole) of N-nitroso-N-(2,2-diphenyl-

cyclopropyl)urea. The mixture was stirred and heated at 750 for two

hours. During this period approximately 30 ml. of gas was evolved and a

white solid precipitated. The solid was isolated by filtration and

purified by recrystallization from acetone, 0.14 g., m.p. 133-133.50.

It was shown to be urea by its infrared spectrum and mixed melting point

with authentic urea

After isolation of urea, 20 ml. of pentane was added to the

remainder of the reaction mixture* Cooling precipitated a white solid

and isolation by filtration gave 1.43 g., 34 per cent yield of the

expected pyrazoline, m.p. 147-1490 after recrystallization from methanol;

Nmax 320 mpt 10t,900, 3.00p, 5,76p, 5.99p, and 6.52p.
Anal. Calcd. for C23H24N204: C0 70.39; H, 6.16; N, 7L14,

Found: C, 70.20; H, 6.30; N, 6.88.














IV. SUMMARY


Both thermal and base decomposition of N-nitroso-N-(2,2-

diphenylcyclopropyl)urea has been studied.

Initially, the base decomposition was employed to generate

2,2-diphenyldiazocyclopropane which could then lead to 2,2-diphenyl-

cyclopropylidene; however, it was found that the diazocyclopropane

was unstable and spontaneously decomposed. In hydrocarbon solvents it

was noted that the nitrosourea decomposition resulted in nearly quan-

titative formation of 1,1-diphenylallene whereas olefinic solvents

gave, in addition to appreciable quantities of the allene, the spiro-

pentane products anticipated from the reaction of 2,2-diphenylcyclo4

propylidene with the double bond. The suggested spiropentane structures

were substantiated by spectral properties and in one instance by

alternate synthesis.

It has been demonstrated that the formation of 1,1-diphenyl-

allene in this base decomposition results from at least two distinct

precursors, only one of which is capable of reaction with an olefin to

give a spiropentane. Evidence is presented to identify the two pre-

cursors as 2,2-diphenyldiazocyclopropane and 2,2-diphenylcyclopropylidene.

The diazocyclopropane was shown to undergo a typical nucleophilic

reaction of diazoalkanes by pyrazoline formation with diethyl fumarate.

Although the isolation of carbenoid products definitely suggests a

cyclopropylidene as the second allene precursor, more direct evidence

was obtained by generation of the reactive intermediates in olefins of









differing nucleophilicity. This allowed measurement of the selectivity

and therefore nature of the intermediate responsible for the spiro-

pentanes. Analysis of these experimental results were in keeping

with expectations for a cyclopropylidene intermediate since they

demonstrated that 2,2-diphenylcyclopropylidene is an unsymetrical

electrophilic species which exhibits a dominating steric effect. The

reaction of this cyclopropylidene was shown to be stereospecific in

its reactions with cis- and trans-2-butene.

Thermal decomposition of N-nitroso-N-(2,2-diphenylcyclopropyl)-

urea was similarly shown to produce nearly quantitative amounts of

1,1-diphenylallene. The origin of this allene was shown to completely

parallel that of the base decomposition. This new synthetic method

provides a cleaner, strong-base-free reaction for the production of a

diazocyclopropane and cyclopropylidene.













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38


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BIOGRAPHICAL SKETCH


Michael Howard Grasley was born January 24, 1937, in Barberton,

Ohio. In June, 1954, he was graduated from Lash High School,

Zanesville, Ohio. The following September, he entered Ohio University

for undergraduate study leading to the degree of Bachelor of Science.

After receiving the degree in June, 1958, he enrolled in the Graduate

School of the University of Kentucky. This led to the degree of Master

of Science. He then continued his education by entering the Graduate

School of the University of Florida in the fall of 1960. During graduate

study, he held both graduate and research assistantships in the Depart-

ment of Chemistry.














This dissertation was prepared under the direction of the

chairman of the candidate's supervisory committee and has been

approved by all members of that committee. It was submitted to the

Dean of the College of Arts and Sciences and to the Graduate Council,

and was approved as partial fulfillment of the requirements for the

degree of Doctor of Philosophy.



August 10, 1963



Dean, College of Arts and Scien es




Dean, Graduate School


Supervisory Committee:



Chairman










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TITLE: Generation and reactions of 2 2-diphenyldiazocyclopropane. (record
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