Sterically encumbered chiral amino alcohols for the titanium catalyzed asymmetric alkylation of benzaldehyde

Abstract

Sterically encumbered chiral l-amino alcohols with secondary amines and tertiary alcohols catalyze the enantioselective alkylation of benzaldehyde with diethyl zinc. Using 2mol% of amino alcohol catalyst predominantly gave (R)-1-phenylpropanol with enantiomeric excesses of up to 61%. Using the in situ prepared titanium complex at 2mol% as catalyst also favored the (R)-enantiomer with enantiomeric excesses of up to 73%. In almost all cases, the addition catalyzed by the titanium complex exhibited higher enantioselectivity than that of the amino alcohol ligand alone.