Enantioselective Radical‐Type 1,2‐Alkoxy‐Phosphinoylation to Styrenes Catalyzed by Chiral Vanadyl Complexes

Abstract

AbstractA series of vanadyl complexes bearing 3‐t‐butyl‐5‐bromo, 3‐aryl‐5‐bromo, 3,5‐dihalo‐, and benzo‐fused N‐salicylidene‐tert‐leucinates was examined as catalysts for 1,2‐alkoxy‐phosphinoylation of 4‐, 3‐, 3,4‐, and 3,5‐substituted styrene derivatives (including Me/t‐Bu, Ph, OR, Cl/Br, OAc, NO2, C(O)Me, CO2Me, CN, and benzo‐fused) with HP(O)Ph2 in the presence of t‐BuOOH (TBHP) in a given alcohol or cosolvent with MeOH. The best scenario involved the use of 5 mol % 3‐(2,5‐dimethylphenyl)‐5‐Br (i.e., 3‐DMP‐5‐Br) catalyst at 0 °C in MeOH. The desired catalytic cross coupling reactions proceeded smoothly with enantioselectivities of up to 95 % ee of (R)‐configuration as confirmed by X‐ray crystallographic analysis of several recrystallized products. The origin of enantiocontrol and homolytic substitution of the benzylic intermediates by vanadyl‐bound methoxide and radical type catalytic mechanism were proposed.