13C magnetic resonance studies. 124. Preparative ring expansions of bicyclic ketones by homoketonization of cyclopropoxide analogs

Abstract

Homoketonization of some readily prepared cyclopropoxides provides a new synthetic method for ring expansion of the [2.2.1] and [2.2.2] ring systems. Cyclopropanation of the trimethylsilyl enol ethers derived from a variety of polycyclic ketones affords the required cyclopropyl silyl ethers, which may be ketonized directly or hydrolyzed to the corresponding cyclopropanols before ketonization. The results for fourteen examples serve to define the scope of the ring expansion process, and the silyl enol ethers, cyclopropyl silyl ethers, and most of the corresponding cyclopropanols have been characterized by 13Cmr. The stereochemistry of the ketonization leading to ring expansion has been established by deuterium labelling experiments.