A catalytic aza-Nazarov cyclization between 3,4-dihydroisoquinolines and α,β-unsaturated acyl chlorides has been developed to access α-methylene-γ-lactam products in good yields (up to 79%) as single diastereomers. The reactions proceed efficiently when AgOTf is used as an anion exchange catalyst with a 20 mol % loading at 80 °C. Computational studies were performed to investigate the reaction mechanism, and the findings support the role of the -TMS group in reducing the reaction barrier of the key cyclization step.