Metalated epoxides as carbenoids - Further advances in the stereospecific synthesis of spirocyclopropanes

The intramolecular cyclopropanation of beta,gamma -unsaturated metalated ep oxides derived from 11 yielded the highly strained tricyclic intermediates 7. The facile hydrolysis of the latter species afforded the alpha -keto spi rocyclopropanes 8 in a stereospecific fashion. Indeed, the stereochemistry of the starting alkenes 11d-e governs the relative configuration of the cyc lopropanes 8d-e. Furthermore, these spiro systems readily underwent acid-me diated ring opening by various nucleophiles, leading to the substituted eno nes 12.