3,3-Dimethyl-3,4-dihydroisocarbostyryl azine (2) has been synthesized by oxidation of l-hydrazino-3,3-dimethyl-3,4-dihydroisoquinoline (1). The crystal and molecular structures of compound 2 were determined. It has been established that in the solid state, compound 2 exists as an azine tautomer. The IR, electronic, and NMR spectral data indicate that in solution the tautomeric form of 2 does not change. A possible mechanism of the oxidation of 1 to 2 is suggested. © 1996, Plenum Publishing Corporation. All rights reserved.