GENERATION AND REACTIONS OF
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
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
ACKNOWLEDGMENTS. . . . . . . . . . . . i
LIST OF TABLES . . . . . . .. . .. . . . iv
LIST OF FIGURES. . .. . . . . . . .. . . . v
I. INTRODUCTION . . . . . . . . . . . 1
IX. RESULTS AD DISCUSSION . . . . . . . . . 4
III EXPERIMENTAL . . . .. . . . . . . . . 24
IV. SUMMARY. . . . . . . . . . . . . . 34
LIST OF REFERENCES . . . . . . . . . . . . 36
BIOGRAPHICAL SKETCH. . . . . . . . . . . . . 39
LIST OF TABLES
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
1. Plot of Spiropentane/Allene Versus trans-2-Butene
Concentration . . . . . . . . . .. 14
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
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-
+ CH3Li + C=CH2
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
CO2H .. SO2 C3 A
R- 2) aN3R -
H 0 N=O0
N=C=O I N-02 -C-N
R- R- R
R R R
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
IIc-tN2 Li002 5 G 2
R-> 0 R 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
II + LiOC2H5 + C=CH2 + IV
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
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.
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
Isobutylene 2.75 (sharp) 8.48 9.31 8.74
3.0 (broad) 9.54 9.00
cis-2-Butene 2.89 (sharp) 8.63 9.0 8.97
butene 2.91 (sharp) 8.52 -- 8.90
Cyclohexcne 2.90 (broad) 8.56 8.65d -
aTau values from tetramethylsilane.
bBroadens on dilution.
dBroad band, 8.0 to 9.5.
chlorospiropentanel5 and disagreement with values for several cyclo-
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
R = C6%5
upon admixture, had identical g.l.p.c. retention times and identical
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
Consider the following reaction scheme, For the sake of clarity
Sk 2-Butene Spiro-
+ k4"2 k pentane
Lithium Ethoxide V
k 2 R CC
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)
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)
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
Spiropentane k2 (Bute
Allene klk3 + k3 + (Butene)
*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.
Results of the Reaction of N-Nitroso-iN-(2,2-Diphenylcyclopropyl)urea
with Lithium Ethoxide in Varying trans-2-Butene Concentrations
t-2-Butene, aoles/liter Allene
Spiropentane / Allene
Plot of Spiropentane/Allene Versus trans-2-
(Curve calculated from equation (4) (solid
line): 0, experimental results.)
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
II + Diethyl Fumarate LiOC2H 1 1
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-
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.
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
aMeasured in competition with cyclohexene.
bThese data are taken from Close and Schwartz.22
C6H, V 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
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
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
C61 CN2 reflux C615
+ (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,
+N1-C-FH2 Diethyl 80oC 02C2I-5
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,
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.
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-
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,
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
of 2,2-Diphenylcyclopropylidene Adducts
Yield Retention Infrared Infrared Calcd. Found
Acceptor M.P. (g.l.p.c.) Timesc Absorption Absorption C H C H
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
cFor g..lp.c. conditions, see "Analyses for spiropentanes and 1,1-diphenylallene" in the Experimental
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
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
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
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
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
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.
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
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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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
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TITLE: Generation and reactions of 2 2-diphenyldiazocyclopropane. (record
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