Multisubstituted α,β-Unsaturated γ-Lactones from 1-Chlorovinyl p-Tolyl Sulfoxides and tert-Butyl Carboxylates Using Pummerer-Type Cyclization as the Key Reaction

The addition reaction of 1-chlorovinyl p-tolyl sulfoxides, derived from aldehydes and chloromethyl p-tolyl sulfoxide, with the lithium enolate of tert-butyl carboxylates gave adducts in quantitative yields. Treatment of the adducts with trifluoroacetic anhydride in the presence of sodium iodide resulted in the formation of gamma-lactones bearing a p-tolylsulfanyl group at the gamma-position through Pummerer-type cyclization. Oxidation of the sulfanyl group to the sulfinyl group followed by thermal syn-elimination gave alpha,beta-unsaturated gamma-lactones (gamma-butenolides) in moderate to good yields. Trapping the intermediates of the addition reaction with iodoalkanes gave alkylated adducts, from which alpha,gamma- and beta,gamma-disubstituted gamma-butenolides were obtained. These procedures provide a good way to synthesize multisubstituted gamma-butenolides from aldehydes.