New samarium diiodide-induced ketyl couplings -: From analogous reactions to serendipitously discovered processes

Analogous applications of samarium diiodide as a promoter for ketyl cyclizations led to the discovery of several new and synthetically interesting reactions. Whereas samarium ketyl cyclizations with alkyne and allene units could be expected-though they have not been known before-the unplanned cyclization of the ketyl towards an aromatic ring uncovered a new mode of reaction. The resulting hexahydronaphthalene derivatives were formed in excellent diastereoselectivities and are synthetically very valuable building blocks. This new method was systematically investigated and extended to polycyclic compounds and those with heteroatoms in the spacer between the carbonyl group and the aromatic ring. The cyclizations involving indole and pyrrole derivatives are most promising for the stereoselective construction of alkaloid skeletons.