Diastereoselective synthesis of the A-B-C tricyclic ring structure of stemocurtisine

The diastereoselective synthesis of the A-B-C tricyclic ring structure of the Stemona alkaloid stemocurtisine is described. This tricyclic precursor to the natural product was obtained in 19 steps from a known vinyl iodide. Attempts to prepare the C-3a-C-11 ether moiety of this alkaloid through a photochemically induced oxidative cyclization method were unsuccessful because of the cleavage of the A-ring.