Dehydrogenation of tetrahydrospiro[3H-2-benzazepines] under mild conditions as a new route to dihydro derivatives

The oxidation of 1,2,4,5-tetrahydrospiro[3H-2-benzazepine-3,1′-cycloalkanes] by KMnO4 under phase-transfer conditions gives the corresponding substituted cyclic imines in high yields.