A Formal [4+2] Cycloaddition of Sulfur-Containing Alkylidene Heterocycles with Allenic Compounds.

In this study, we report an enantioselective synthesis of sulfur heterocycles containing dihydro-2H-pyran moiety. The synthetic strategy is based on quinidine catalyzed formal [4+2] cycloaddition between 3-alkylidene benzo[b]thiophenes and allenoates affording the corresponding cycloadducts in high yields (up to 95 %) with high enantioselectivity (up to 99 % ee). Moreover, cycloadducts can be isolated by simple filtration from the reaction media.