New Asymmetric Approach to Natural Pyrrolizidines: Synthesis of (+)-Amphorogynine A, (+)-Amphorogynine D, and (+)-Retronecine
作者:Caroline Roche、Katarína Kadlečíková、Amaël Veyron、Philippe Delair、Christian Philouze、Andrew E. Greene、David Flot、Manfred Burghammer
DOI:10.1021/jo050983o
日期:2005.10.1
Three natural pyrrolizidines, (+)-amphorogynines A and D and (+)-retronecine, have been prepared from a common lactam intermediate. This central compound, in turn, was synthesized in diastereomerically enriched form through a highly selective [2 + 2]-cycloaddition of dichloroketene with a chiralenol ether, followed by Beckmann ring expansion and reduction. Subsequent stereocenters were then cleanly