Chiroptical properties and synthesis of enantiopure cis and trans pterocarpan skeleton.

The first enantioselective synthesis of trans-(6aS,11aR)-pterocarpan [(+)-2] and its conversion to cis-(6aS,11aS)-pterocarpan [(+)-1] was achieved starting from racemic 2'-benzyloxyflavanone (rac-3). Their stereochemistry was deduced by X-ray analysis of the ketal intermediate (-)-5a. The CD study of (+)-1 and (+)-2 allows the configurational assignment of similar pterocarpan derivatives by CD spectroscopy. Copyright 2003 Wiley-Liss, Inc.