Regio- and Diastereodivergent [4 + 2] Cycloadditions with Cyclic 2,4-Dienones.

By employing activated alkenes with bulky α-functional groups, such as α-cyano-α,β-unsaturated ketones and Meldrum's acid-based alkenes, a previously unreported cross-trienamine pathway of cyclic 2,4-dienones is adopted to deliver γ',δ-regioselective [4 + 2] cycloadducts catalyzed by cinchona-derived amines. In addition, a diastereodivergent [4 + 2] cycloaddition reaction is realized with Z-configured 4-alkylideneisoxazol-5(4H)-ones under similar catalytic conditions, even through a three- or four-component cascade process with simple starting materials.