Introduction of a homochiral p-tolylsulfinyl group at an appropriate position in the alkene accelerates the thermal [5C + 2C] intramolecular cycloaddition to beta-silyloxy-gamma-pyrones and, most importantly, leads to excellent levels of diastereodifferentiation. The resulting adducts can be easily desulfinylated to give optically active 8-oxabicyclic[3.2.1]octane intermediates which by virtue of their rich functionalization might be susceptible to elaboration into enantiomerically pure natural products containing seven-membered carbocycles and tetrahydrofurans.