Synthesis of 8-Aminoquinolines by Using Carbamate Reagents: Facile Installation and Deprotection of Practical Amidating Groups
Described herein is the development of practical routes to 8-aminoquinolines by using readily installable and easily deprotectable amidating reagents. Two scalable procedures were optimized under RhIII-catalyzed conditions: i) the use of pre-generated chlorocarbamates and ii) a two-step one-pot process that directly employs carbamates. Both approaches are highly convenient for the gram-scale synthesis of 8-aminoquinolines under mild conditions. Facile deprotection of the synthetically versatile amidating groups was achieved under the Pd-catalyzed transfer hydrogenation conditions with simultaneous deoxygenation of quinoline N-oxides, thus yielding 8-aminoquinolines in excellent overall efficiency.
REARRANGEMENTS OF AROMATIC CARBONYL ARYLHYDRAZONES OF BENZENE, NAPHTHALENE, AND AZULENE
Aromatic carbonyl arylhydrazones have been shown to undergo two kinds of rearrangement in polyphosphoric acid both involving nitrogen-nitrogen bond cleavage.The first proceeds via insertion of the imine portion in the position ortho to the second nitrogen atom to give o-phenylenediamine intermediates: their evolution depends on the nature of the starting substrate.This reaction has been employed for synthesizing the quinoxalines (5) and the phenanthridines (11), and was demonstrated to be intramolecular.The second reaction path is a sigmatropic rearrangment exclusive to electron-rich aromatic carbonyl hydrazones.