Palladium-Catalyzed Asymmetric Allylic C–H Functionalization for the Synthesis of Hydroquinolines through Intermolecular [4+2] Cycloadditions
Kai Wang, Xiangfeng Lin, Yan Liu, Can Li
Abstract
Catalytic asymmetric [4+2] cycloadditions via allylic C–H functionalization are of great interest and importance but remain unexplored. We report herein an intermolecular [4+2] cycloaddition involving the direct Pd(0)-catalyzed allylic C–H functionalization with readily accessible olefin substrates. Key to the success of this reaction is a chiral alkylphosphine ligand, which enables the asymmetric allylic C–H alkylation to deliver a broad range of hydroquinolines in high diastereoselectivities (up to >20:1) and enantioselectivities (up to 98% ee). Control experiments show that allylic C–H functionalization takes place possibly via the concerted proton and two-electron transfer process. This strategy opens a route for synthesizing chiral heterocycles in a straightforward way with readily accessible substrates and minimal functional-group manipulation.