Stereoselective rhodium-catalyzed [3 + 2 + 1] carbocyclization of alkenylidenecyclopropanes with carbon monoxide: theoretical evidence for a trimethylenemethane metallacycle intermediate.

The theoretically inspired development of a Rh-catalyzed [3 + 2 + 1] carbocyclization of carbon- and heteroatom-tethered alkenylidenecyclopropanes (ACPs) with CO for the stereoselective construction of cis-fused bicyclohexenones is described. This study demonstrates that the ring opening of alkylidenecyclopropane proceeds through a Rh(III)-trimethylenemethane complex, which undergoes rate-determining carbometalation through a transition state that accurately predicts the stereochemical outcome for this process. The experimental studies demonstrate the validity of this approach and include the first highly enantioselective reaction involving an ACP to highlight further the synthetic utility of this transformation.