The aza-Prins reaction of 3-vinyltetrahydroquinolines with aldehydes proceeded smoothly in the presence of hydrogen halides, and the tricyclic benzazocine derivatives were isolated in good to high yields. The reaction would proceed through the formation and cyclization of the iminium ion intermediate.

The aza-Prins reaction of 6,7-dimethoxy-3-vinyl-1,2,3,4-tetrahydroquinoline ( 1 ) with 1,2-dicarbonyl compounds proceeded smoothly in the presence of HCl, and the corresponding tricyclic benzazocines were isolated in yields of 20–86%. The reaction proceeded in a stereoselective manner, and the formation of the 2,4- trans isomer was observed. The reaction of 1 with an enantiopure ketoester gave the corresponding tricyclic benzazocine as a mixture of diastereomers. The diastereomers were easily separated and converted to enantiopure tricyclic benzazocines. The synthesis of spirooxindole derivatives was achieved by the reaction of 1 with isatin derivatives.