Evidence for Concert in the Thermal Unimolecular Vinylcyclopropane to Cyclopentene Sigmatropic 1,3-Shift
详细信息 查看全文
- 作者：Joseph J. Gajewski ; Leif P. Olson ; and M. Robert Willcott ; III
- 刊名：Journal of the American Chemical Society
- 出版年：1996
- 出版时间：January 17, 1996
- 年：1996
- 卷：118
- 期：2
- 页码：299 - 306
- 全文大小：445K
- 年卷期：v.118,no.2(January 17, 1996)
- ISSN：1520-5126
文摘
Gas phase pyrolysis ofcis-2,3-dideuterio-trans-(1'-tert-butyl-2'-(Z)-deuteriovinyl)cyclopropaneat 290 
Cgivestrans,trans-3,4,5-trideuterio-1-tert-butylcyclopenteneas the major 1,3-shift product with greater than 90%stereospecificity in an orbital symmetry "allowed"suprafacial-inversion sense after correction for thegeometricisomerization of starting material and the other materials present.The isotopic substitution at the critical sites ofrearrangement eliminates steric or electronic influences ofsubstituents on a biradical pathway as a source of thesuprafacial-inversion stereochemistry observed with more highlysubstituted derivatives. The stereochemical resultscoupled with a normal deuterium kinetic isotope effect(kH/2kD = 1.14 at 311.6C) at the exo-methylene carbon arebest interpreted in terms of a concerted pathway for rearrangement.A less likely alternative is a stereospecificdisrotatory ring opening to a biradical followed by rate-determiningclosure to a five-membered ring. Accompanyingthe rearrangement is geometric isomerization of starting materialresulting from C-1-C-2 bond fission which favorseither the single methylene rotation or a double rotation by a factorof 10 over single rotation at the vinyl-bearingcarbon.
Cgivestrans,trans-3,4,5-trideuterio-1-tert-butylcyclopenteneas the major 1,3-shift product with greater than 90%stereospecificity in an orbital symmetry "allowed"suprafacial-inversion sense after correction for thegeometricisomerization of starting material and the other materials present.The isotopic substitution at the critical sites ofrearrangement eliminates steric or electronic influences ofsubstituents on a biradical pathway as a source of thesuprafacial-inversion stereochemistry observed with more highlysubstituted derivatives. The stereochemical resultscoupled with a normal deuterium kinetic isotope effect(kH/2kD = 1.14 at 311.6C) at the exo-methylene carbon arebest interpreted in terms of a concerted pathway for rearrangement.A less likely alternative is a stereospecificdisrotatory ring opening to a biradical followed by rate-determiningclosure to a five-membered ring. Accompanyingthe rearrangement is geometric isomerization of starting materialresulting from C-1-C-2 bond fission which favorseither the single methylene rotation or a double rotation by a factorof 10 over single rotation at the vinyl-bearingcarbon.