Hexacyclic Indole Alkaloids - A Highly Convergent Total Synthesis of Cuanzine

A novel route to the hexacyclic indole alkaloid cuanzine 1 has been developed. Key synthetic steps include the cyclocondensation of the imine 8 with the dihydrofuran 10 followed by homogeneous-catalyzed hydrogenation, wherein the COOMe group at C(20) serves as a diastereocontrol element in establishing the C(15) stereogenicity. In order to define local energy minima, the conformational space of some intermediates has been explored by empirical force field calculations (MM2).