Transannular [4+3] Cycloadditions of Macrocyclic Epoxy Ketones.

Transannular [4+3] cycloadditions of dienophiles derived from macrocyclic epoxy ketones produce fused ring systems having central cycloheptane subunits. In some cases, the base directly induced cycloisomerization of the epoxy ketones to yield the cycloadducts; in others, the epoxy ketones were transformed into their corresponding enolsilanes before undergoing cycloaddition. Enantiomerically enriched tricyclic arrays were obtained from cycloadditions starting from optically pure epoxy ketones.