Open AccessMechanism of thermal rearrangement of the spiro bicyclo[2.1.0]-pentane-5,2′-methylenecyclopropanes to 6- and 7- methylenebicyclo[3.2.0]hept-1-enes
Author(s) -
David M. Lokensgard,
Dennis A. Dougherty,
Ε. F. Hilinski,
Jerome A. Berson
Publication year - 1980
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.77.6.3090
Subject(s) - pentane , bicyclic molecule , chemistry , trimethylenemethane , isomerization , epimer , stereochemistry , reaction mechanism , bond cleavage , organic chemistry , cycloaddition , catalysis
The thermal rearrangements of the bicyclo[2.1.0]pentane-5,2′-methylenecyclopropanes fall into two classes. The first occurs near 80°C and consists of a double epimerization (“bridge flip”) which is initiated by cleavage of the bridge bond. An alternative mechanism by way of a trimethylenemethane intermediate is ruled out by an isotopic position-marking experiment. The second rearrangement begins to be detected above 120°C. It gives the isomeric 6- and 7-methylenebicyclo[3.2.0]hept-1-enes. Two possible mechanisms can operate in this complex change, but a choice between them is not yet possible.