Stable azomethine imines having a 3,4-dihydroisoquinoline fragment and their cycloaddition to <Emphasis Type="Italic">N</Emphasis>-arylmaleimides

Aroylation of 5,6,8,8a,13,14,16,16a-octahydro1,2,4,5]tetrazino6,1-a:3,4-a′]diisoquinoline or 1,3,4,8b-tetrahydro1,2]diazireno3,1-a]isoquinoline, as well as reactions of 2-(2-bromoethyl)benzaldehyde with aroylhydrazines followed by treatment with triethylamine, led to the formation of stable azomethine imines, aroyl(3,4-dihydroisoquinolinium-2-yl)azanides. 1,3-Dipolar cycloaddition of the latter to N-mesitylmaleimide was stereoselective: the ratio of the trans- and cis-adducts was ∼(3–7): 1, the former prevailing. The reactions with N-arylmaleimides having no ortho-substituents in the aryl group gave the corresponding cis-adducts as the major products trans/cis ratio ∼1: (2.5–10)].