Mild synthesis of enantiomerically pure imidazo-[1,2-a]azepines mediated by Yb(OTf)3

The reaction of various chiral 2,2'-diaryldialdehydes with achiral and chiral 1,2-diamines in the presence of Lewis acids to give imidazo[1,2-a]azepines was investigated. Best results were achieved with Yb(OTf)(3); the reaction outcome is strongly dependent upon the geometric features of both reactants. Kinetic resolution of rac-2,2'-dinaphthyldialdehyde with (R,R)-1,2-diphenyl-1,2-diamminoethane (up to 92% e.e.) was achieved. (C) 2001 Elsevier Science Ltd. All rights reserved.