Sequential Cyclosulfonylation and Alkylation as a Versatile Strategy for Dihydropyran Synthesis

Deprotonation of 3,4-dihydro-6-(p-toluenesulionyl-methyl)-2H-pyran (2) with m-BuLi and alkylation of the lithiated allyl sulfone gives good to excellent yields of monoalkylated products 3. No γ-substitution is observed inthe monoalkylated products. A second deprotonation allows for the introduction of a second alkyl group. Desulfonylation can be effected with either sodium amalgam or sodium/ethanol in THF.