Rhodium(I) Carbene‐Promoted Enantioselective C−H Functionalization of Simple Unprotected Indoles, Pyrroles and Heteroanalogues: New Mechanistic Insights.

A rhodium(I)‐diene catalyzed highly enantioselective C(sp2)−H functionalization of simple unprotected indoles, pyrroles, and their common analogues such as furans, thiophenes, and benzofurans with arylvinyldiazoesters has been developed for the first time. This transformation features unusual site‐selectivity exclusively at the vinyl terminus of arylvinylcarbene and enables a reliable and rapid synthetic protocol to access a distinctive class of diarylmethine‐bearing α,β‐unsaturated esters containing a one or two heteroarene‐attached tertiary carbon stereocenter in high yields and excellent enantioselectivities under mild reaction conditions. Mechanistic studies and DFT calculations suggest that, compared to the aniline substrate, the more electron‐rich indole substrate lowers the C−C addition barrier and alters the rate‐determining step to the reductive elimination, leading to different isotope effect. [ABSTRACT FROM AUTHOR]