Mechanism 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

Creators: Lokensgard, David M.; Dougherty, Dennis A.; Hilinski, Edwin F.; Berson, Jerome A.

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Abstract

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.

Additional Information

© 1980 National Academy of Sciences. Contributed by Jerome A. Berson, February 11, 1980. We thank Prof. Peter B. Dervan, California Institute of Technology, for the suggestion of the variant sequence 47 → 46a → 46 of Scheme VI. Acknowledgment is made to the donors of the Petroleum Research Fund, administered by the American Chemical Society, for partial support of this work. We also thank the National Science Foundation (CHE 76-00416) for partial support and the Biotechnology Resources Program of the National Institutes of Health (RR-798) for its support of the Southern New England High-Field NMR Facility. The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact.

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