α-Regioselective Asymmetric [3 + 2] Annulations of Morita-Baylis-Hillman Carbonates with Cyclic 1-Azadienes and Mechanism Elucidation.

An α-regio-, diastereo-, and enantioselective [3 + 2] annulation reaction of Morita-Baylis-Hillman carbonates of isatins and activated alkenes with a bulky electron-withdrawing 1,2-benzoisothiazole 1,1-dioxide or 1,2,3-benzoxathiazine 2,2-dioxide motif is reported, furnishing an array of spirooxindoles (>19:1 dr, up to >99% ee) catalyzed by cinchona-derived tertiary amines. Density functional theory calculation studies have been conducted to elucidate the originality of the α-regioselective annulations.