Chiral aminoborane as a chiral proton source for asymmetric protonation of lithium enolates derived from 2-arylcycloalkanones

Abstract

Reaction of lithium enolates of 2-arylcycloalkanones 2 with (R,R)-aminoborane 1, prepared from (1R,2R)-1,2-diaminocyclohexane 4 and PhBCl₂, gives the corresponding optically active ketones 3 with up to 93% ee; this is the first example of enantioselective protonation using a metal-containing chiral proton source.