Synthesis of (-)-(R)-angustureine by formal alkynylation of a chiral β-amino ester

A new synthesis of (-)-angustureine is described, featuring an annulation and fragmentation sequence that formally results in alkynylation of a beta-amino ester. The six-step sequence from a readily available chiral beta-amino ester to the natural product was achieved in 46% yield, with no protecting groups and three purifications. (C) 2013 Elsevier Ltd. All rights reserved.