Group Title: 2, 4-ethano- and 2,4-etheno-3-alkoxy-tris-homocyclopropenyl cations, orientation and stereochemistry of nucleophile capture
Title: The 2, 4-ethano- and 2,4-etheno-3-alkoxy-tris-homocyclopropenyl cations, orientation and stereochemistry of nucleophile capture
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Title: The 2, 4-ethano- and 2,4-etheno-3-alkoxy-tris-homocyclopropenyl cations, orientation and stereochemistry of nucleophile capture
Physical Description: x, 131 leaves. : illus. ; 28 cm.
Language: English
Creator: Nielsen, Warren Charles, 1945- ( Dissertant )
Battiste, Merle A. ( Thesis advisor )
Tarrant, Paul ( Reviewer )
Dolbier, William R. ( Reviewer )
Stoufer, Robert C. ( Reviewer )
Allen, Charles M. ( Reviewer )
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 1974
Copyright Date: 1974
Subjects / Keywords: Solvolysis   ( lcsh )
Chemistry thesis Ph. D
Dissertations, Academic -- Chemistry -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
Abstract: Solvolyses of endo, anti- tri cycl o 3. 2 . 1 . 2 ' " .octanyl derivatives, i.e. , hydrogen, vinyl, and p-anisyl substitution at the bridge C 8 position, have been shown to afford rearranged products {endo C 2 or C^ attack) almost exclusively (>99%). Concentration of positive charge at the C 2 and C^ positions of the respective intermediate tri s-homocycl opropenyl cations might be an explanation; an alternative view stresses the importance of strain relief in the transition state for solvent capture of the non-classical cations. In contrast to the above results, acidic hydrolysis of 8 ,8-dimethoxy-endo-tri cycl o 3. 2 . 1 . 2 ' k octane' (I) yields the expected ketone II with no evidence for the formation of a rearranged hydroxyether. This suggests that the charge stabilizing ability of the methoxyl group at the bridge carbon may well be overwhelming the skeletal bias of the transition state for solvent capture. Saturated ketal I was treated with dichloroal umi num hydride to yield the sz/n-methyl ether exclusive of its anti epimer. Under the same reaction conditions, the unsaturated ketal , 8,8-dimethoxy-endo-tricyclo 2,1+ oct-6-ene (III), gave the unsaturated syn- methyl ether IV as the major product along with l-methoxy-endo-6-chl orotri cycl o 3. 3 . . 2 ' 8 - oct-3-ene (V) as a minor product. Traces of endo- 6- me thoxyand endo-6-chlorotricyclo3. 3. . 2 ' 8 oct-3-enes,(VI) and (VII), were also detected. The trace components are attributed to the intermediacy of unsaturated anti-methyl ether VIII as evidenced by its authentic synthesis and subsequent exposure to the reactions conditions. The predominance of bridge C 8 anti hydride attack and formation of endo unsaturated rearranged chloride V argue strongly for the intermediacy of a delocalized system with charge concentrated at C a due to methoxyl stabilization. The transient formation of the unsaturated anti methylether VIII could result from hydride attack upon a bis-homocyclopropenyl cation, whose mode of formation has several potential routes. Use of an 8:1 molar ratio of the aluminum chloride/ lithium aluminum hydride reagent with the respective saturated and unsaturated methyl ketals I and III produced good yields of the saturated and unsaturated rearranged methoxy chlorides IX and V, both of which were solvolyzed at 100° in aqueous ethanol. For the unsaturated chloride V, the major product, cycloheptatriene , and a mixed ethoxy-methoxy ketal fraction of the original tri cycl o 3. 2 . 1 . 2 » k octenyl structure were isolated. Cy cl ohep ta tr i ene is the expected product from the well-known decarbonyl ati on of the unsaturated ketone. According to PMR analysis the mixed ketal fraction consisted of 89% arcti-ethoxy-syrc-methoxy unsaturated ketal and 11% antimethoxy- st/n-ethoxy ketal. Solvolysis of the saturated chloride IX in aqueous ethanol produced the saturated ketone II as the major product with a mixed ketal fraction consisting of 96% anti-ethoxy-syn-methoxy ketal and 4% anti-methoxy-syn ethoxy ketal . The results obtained strongly indicate that the same cations are being generated from the respective reactions of the saturated and unsaturated ketals I and III with dichloroaluminum hydride and aqueous acid, as well as in the solvolyses of the saturated and unsaturated rearranged methoxy chlorides IX and V. The electronic structure of these ions has now been radically altered with respect to the parent ions in that positive charge del ocal i zati on is not as extensive, giving a more localized or concentrated charge at the methoxyl bridge carbon. The cyclopropyl del ocal i zati on may even have been weakened to the point where nucleophiles are able to penetrate and attack the bridge from the syn as well as anti face of the bridge. Thus an electronic effect, and not steric bias, is the overwhelming factor in determining the orientation and stereochemistry of solvent or nucleophilic attack on the 2,4-ethano- or 2 ,4-etheno-3-al koxy- tri s-homocycl opropeni urn cations
Thesis: Thesis--University of Florida.
Bibliography: Bibliography: leaves 125-130.
General Note: Typescript.
General Note: Vita.
 Record Information
Bibliographic ID: UF00098345
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: alephbibnum - 000869114
notis - AEG6136
oclc - 014237878


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