Enantiopure N-sulfonylamino alcohols and their copolymers as chiral auxiliaries for the highly enantioselective allylboration of aldehydes

Abstract

Enantioselective synthesis of homoallylic alcohols by nucleophilic addition of chirally modified allylboron reagents to aldehydes was investigated. Reaction of enantiopure N-sulfonylamino alcohols ( 1a, 1b, 3a, 4a) with triallylborane gave the chiral allylboration reagents. Aldehydes were converted to enantioenriched homoallylic alcohols with the reagents. Polymer-supported chiral allylboron reagents were also prepared from triallylborane and crosslinked polymers having chiral N-sulfonylamino alcohol moieties ( 5–8). These polymeric reagents reacted with aldehydes to give optically active homoallylic alcohols in high chemical yield with high enantioselectivities. Optical yield up to 92% ee was obtained by the use of polymeric chiral ligand 7 derived from d-camphor. The potential of this type of approach in asymmetric synthesis is discussed.