Intermolecular Rhodium-Catalyzed [3+2+2] Carbocyclization of Alkenylidenecyclopropanes with Activated Alkynes: Regio- and Diastereoselective Construction of <i>cis</i>-Fused Bicycloheptadienes

Abstract

Polycyclic structures that contain seven-membered carbocycles constitute important structural motifs that are ubiquitous in several classes of bioactive natural products. We have developed the first regio- and diastereoselective intermolecular rhodium-catalyzed [3+2+2] carbocyclization of carbon- and heteroatom-tethered alkenylidenecyclopropanes with mono- and disubstituted alkynes for the construction of cis-fused bicycloheptadienes. This study delineates some of the critical features for controlling regioselectivity in this process and demonstrates that E-alkenes can be incorporated in a stereospecific manner to afford products with up to three new stereogenic centers. The latter feature is particularly significant given that related carbocyclization reactions are often limited in this respect.