Electrophile-Induced Cyclization of ortho-Azido Propynyl Benzenes to Quinolines

Significance

Following the previous report on the synthesis of isoquinolines from 2-alkynyl ­benzyl azides (Y. Yamamoto and co-workers Angew. Chem. Int. Ed. 2007, 46, 4764), the authors now provide the analogous result for the synthesis of substituted quinolines from 2-azido-2-(2-propynyl)-benzenes. After extensive optimization in terms of solvents, electrophiles and catalyst, and an excellent discussion on interpreting these optimization results, the conditions shown in the scheme were established. The substrate scope was well studied, and yields range from moderate to quantitative. The resulting 3-halo-substituted quinoline products are clearly poised for further manipulations, such as C-C bond-forming cross-coupling reactions.