Studies on the Total Synthesis of the Saponaceolides. 1. Enantioselective Synthesis of the Spiroketal Subunit.

An asymmetric synthesis of the tricyclic spiroketal subunit of the saponaceolides is described in which the absolute stereochemistry at C-2' and C-6' is established through a conformationally and stereoelectronically controlled cyclization of a dihydroxyketone pyran Intermediate.