Dichloroketene−Chiral Olefin-Based Approach to Pyrrolizidines:  Highly Stereocontrolled Synthesis of (+)-Amphorogynine A

Abstract

[reaction: see text] A highly stereoselective route to (+)-amphorogynine A, a novel pyrrolizidine recently isolated from the New Caledonian plant Amphorogynine spicata, has been realized. The key step in the approach is a diastereoselective [2 + 2] dichloroketene-chiral enol ether cycloaddition (dr >or= 93:7) to access a dichlorocyclobutanone intermediate, which is converted into the alkaloid natural product via a pyrrolidinone derivative.