The electron-rich methoxy/silyloxy diene undergoes a thermal Diels–Alder reaction with electron-poor acrylonitrile. The regioselective cycloaddition places CN in the relationship shown in C. Aqueous acid hydrolyses the silyl enol ether and eliminates methanol, converting the initial cyclohexene into a cyclohexenone. The resulting **CN-substituted enone is C**; the nitrile is retained rather than lost as in B.
