Scandium-Catalyzed Cascade Cyclization to Produce Cyclobutane-Fused Tetrahydroquinoline, Chromane, Thiochromane, and Tetrahydronaphthalene Derivatives

We have succeeded in the highly diastereoselective synthesis of cyclobutane-fused multicyclic compounds using a scandium-catalyzed cascade cyclization. Using 3-10 mol% of scandium(III) triflate [Sc(OTf)(3)], various cyclobutane-fused tetrahydroquinoline derivatives as well as its chromane, thiochromane, and tetrahydronaphthalene analogues were obtained in good to excellent yields. Derivatizations of the reaction products, as well as the plausible reaction mechanism, are also discussed.