A computational study on cobalt-catalyzed allylic substitution of racemic allylic carbonates with amines: inner-sphere C–N reductive elimination and origins of regio- and enantioselectivities

Abstract

Cobalt/bisoxazolinephosphine-catalyzed allylic substitution of racemic allylic carbonates with amines is a highly efficient method for the synthesis of allylic amines with exclusive branched regioselectivity and excellent enantioselectivity. In this study, density functional theory calculations have been conducted to elucidate the detailed reaction mechanism and to shed light on the source of the selectivities. The computations reveal that the reaction starts with C–O oxidative addition via the S_N2 back-side attack pathway, which is followed by CO₂ extrusion to afford the methoxide-coordinated allyl-Co(III) species. C–N bond formation was found to occur via inner-sphere C–N reductive elimination facilitated by the five-membered transition states, rather than the outer-sphere nucleophilic attack pathway. The calculations reproduced very well the experimentally observed regio- and enantioselectivities, which are mainly caused by the steric repulsions between the allylic moiety and the bisoxazolinephosphine ligand.