Facile synthesis of vicinal diamines via oxidation of N-phenyltetrahydroisoquinolines with DDQ

The oxidation of N-phenyltetrahydroisoquinolines occurs rapidly with DDQ. Under ambient conditions and in the presence of nitromethane, the corresponding beta-nitroamine derivatives are isolated in good to excellent yields. Variation in the electronic nature of the isoquinoline and the N-phenyl substituent showed that a broad range of substituents are tolerated, with electronic communication between the isocluinoline aromatic ring and the C1 carbon being stronger than with the N-aryl ring. Reduction of the beta-nitroamines to the corresponding novel chiral vicinal diamines are straightforward, Examination of the reaction by H-1 NMR spectroscopy suggested that the reaction proceeds via an iminium ion, which then reacts with nitromethane upon work-up. This information was used to shorten the required reaction time. (C) 2009 Elsevier Ltd. All rights reserved.