NEW SYNTHETIC METHODOLOGY USING ORGANOSULFUR COMPOUNDS

Electron-deficient 3-sulfur-substituted 2-pyrones are shown to cycloadd with high stereoselectivity to electron-rich vinylic ethers, vinylic thioethers, and 1,3-dioxoles under sufficiently mild conditions to allow isolation of the initial, bridged, bicyclic lactone adducts. These structurally and stereochemically rich bicycloadducts are easily converted into highly functionalized cyclohexenes as exemplified by high yield syntheses of chorismic acid, 4-epi-shikimic acid, and also la, 25-dihydroxyvitamin D3. © 1990, IUPAC.