Silver(I)-Catalyzed Oxidative Intramolecular Cyclopropanation: Access to Complex Tricyclo[3.3.1.0]nonanediones via Semipinacol-Type Rearrangement.

An unconventional Ag(I)-catalyzed intramolecular cyclopropanation of prochiral alkyne-tethered cyclohexadienones has been developed using simple perchloric acid as an external oxidant. The transformation involves the formation of a perchloryloxy vinyl-silver species, which then proceeds through either intramolecular conjugate addition or an α-oxo silver carbene pathway to yield cyclopropane fused tricyclic enones with high diastereoselectivity. In the case of C-tethered cyclohexadienones, the reaction proceeds further via acid mediated semipinacol-type rearrangement to give complex and highly strained tricyclo[3.3.1.0]nonanediones. This cascade annulation has wide functional-group tolerance and broad substrate scope. Late-stage functionalization of estrone was also demonstrated with excellent diastereoselectivity.