Cu(I)‐Catalyzed Enantioselective γ‐Boryl Substitution of Trifluoromethyl‐ and Silyl‐Substituted Alkenes

Abstract

Asymmetric γ-boryl substitution of trifluoromethyl-and silylsubstituted alkenes has been investigated. A variety of substrates were reacted with bis(pinacolato)diboron in the presence of a copper(I) salt and optically active C 1 symmetric QuinoxP*-type bisphosphine ligand as the catalyst. The optically active silyl-substituted gem-difluoroallylboronates products bearing a stereogenic CÀ B bond, which have never been synthesized before, were obtained in good yield with high enantioselectivity (up to 83 % and up to 86 % ee, respectively). The resulting allylboron compounds undergo a stereoselective allylboration with a range of aldehydes to afford chiral silyl-and difluoromethylene-containing homoallylic alcohols without significant loss in their enantiomeric purity. The resulting silyl groups in the derivatives can serve as cross-coupling sites, allowing further transformation into structurally complex fluorinated chiral molecules.

P-Stereogenic Phosphorus Ligands in Asymmetric Catalysis

“…Optically active α-allylboronates are an important class of organoboron compounds, because they can be converted in almost perfect stereospecificity into chiral building blocks of natural products and bioactive compounds. Ito and co-workers have reported many efficient and versatile reactions for the synthesis of this class of compounds from readily available starting materials. ,,− Their methodology is based on the discovery of Cu-catalyzed asymmetric S N 2′-type allylic substitution reactions with boryl nucleophiles using several P-stereogenic phosphorus ligands.…”