Synthesis of naturally occurring o-heterocyclic compounds of biological activity

Abstract

Abstract The total synthesis of (−)-cabenegrin A-I was achieved via (−)-6a R ,11a R maackiain, which was obtained by optical resolution of racemic maackiain using S -(−)-alpha-methylbenzyl isocyanate. The synthesis of rac -maackiain was performed both with the Heck oxyarylation of 7-benzyloxy-2 H -chromene and the BF 3 OEt 2 mediated ring closure of isoflavan-4-ol derivatives, the latter of which provided much higher yields. The first enantioselective synthesis of trans -6a S ,11a R -pterocarpan and its conversion to cis -6a S ,11a S -ptarocarpan was also presented starting from racemic 2'-benzyloxyflavanone. Their stereochemistry was deduced by circular dichroism (CD) as well as by X-ray analysis of the ketal intermediate.