Four component synthesis of (Z)-4-alkoxy-1,3-dimethylalk-2-enyl methyl sulfones: on the intermediacy of sultines (3,6-dihydro-1,2-oxathiin-2-oxides) arising from suprafacial hetero-Diels–Alder additions of sulfur dioxide

The reactions of (E,E)-1-benzyloxy-2-methylpenta-1,3-diene (9) with 3,3-dimethyl-2-(trimethylsilyloxy)butene and (Z)-3-(trimethylsilyloxy)pent-2-ene in SO2 and a Lewis acid give silyl sulfinates that are quenched with MeI to generate the corresponding (Z)-4-benzyloxy-1,3-dimethylalk-2-enyl methyl sulfones with unlike relative configuration at C-1 and C-4 (by X-ray diffraction studies), in support of processes involving the intermediacy of a sultine arising from the suprafacial hetero-Diels–Alder addition of SO2 to diene 9.