Stereoselective Synthesis of Complex Polyenes through Sequential α‐/β‐C−H Functionalization of trans‐Styrenes

Abstract

AbstractSequential C−H functionalization of molecules containing multiple C−H bonds can efficiently lead to structural diversity. Herein we present the first chelation‐assisted sequential α‐/β‐C−H functionalization of E‐styrenes with simple alkenes and alkynes in excellent regio‐ and stereo‐selectivity. The process involves α C−H functionalization by six‐membered exo‐cyclopalladation to result in tri‐ and tetrasubstituted 1,3‐dienes and β C−H functionalization through seven‐membered endo‐cyclopalladation to produce tetra‐ and pentasubstituted 1,3,5‐trienes in up to 97 % yield with up to >99/1 E/Z selectivity, both enabled by the chelation assistance of pyrazinamide. The protocol is demonstrated to be widely applicable, tolerant to a wide range of functional groups and bioactive fragments, and suitable for gram‐scale synthesis as well as one‐pot and two step preparation of trienes. Mechanistic experiments and density functional theory (DFT) calculations were performed to elucidate the selectivity and reactivity.