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(sp 2 )-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.