The addition of Lewis acids changes the path of the reaction of N-vinylpyrroles with 3,4-dihydroisoquinoline-N-oxides: formal (3 + 3)-cycloaddition proceeds instead of (3 + 2)-cycloaddition. In the case of benzoyl(3,4-dihydroisoquinolin-2-ium-2-yl)amides, reaction path does not change in the same conditions, but changing of the diastereoselectivity occurs and other diastereomer of (3 + 2)-cycloaddition became predominant.