Total synthesis of (+)-manzamine A.

A novel synthetic route to (+)-manzamine A was developed. It highlights an amazingly efficient construction of a highly strained 15-membered ring across a cyclohexenone ring with the aim of installing the requisite functionalities in a completely stereocontrolled manner. Other key features include a stereoselective Diels-Alder reaction of an optically active butenolide, construction of the 15-membered ring by intramolecular Mitsunobu reaction of a nosyl amide, [3,3]-sigmatropic rearrangement of allyl cyanate for stereoselective introduction of nitrogen functionality at a sterically congested position, and a ring-closing metathesis in the presence of labile functional groups.