Enantio- and Diastereoselective Copper-Catalyzed Allylboration of Alkynes with Allylic gem-Dichlorides

Abstract

A highly chemo-, regio-, enantio- and diastereoselective coupling of terminal alkynes, bis(pinacolato)diboron and allylic gem-dichlorides is reported. The method uses a chiral NHC−Cu catalyst which generates, in a single step, synthetically versatile chiral skipped dienes bearing a Z-alkenyl chloride, a trisubstituted E-alkenyl boronate and a bis-allylic stereocenter. Allylic gem-dichlorides are shown to be efficient substrates for catalytic asymmetric allylboration of alkynes. The method employs a chiral NHC−Cu catalyst capable of generating in a single step chiral skipped dienes bearing a Z-alkenyl chloride, a trisubstituted E-alkenyl boronate and a bis-allylic stereocenter with excellent levels of chemo-, regio- enantio- and diastereoselectivity. This high degree of functionalization makes these products versatile building blocks as illustrated with the synthesis of several optically active compounds. DFT calculations support the key presence of a metal cation bridge ligand–substrate interaction and account for the stereoselectivity outcome