Friedel–Crafts Chemistry. Part 46. Unprecedented Construction of Tricyclic Pyrazolo[3,4-b]quinolines, -[1,8]naphthyridines, -azepines, -azocines, -pyrido[3,2-g]azocines, and pyrazolo[3,4-b]azonines via Friedel–Crafts Ring Closures

Abstract

A series of keto-substituted pyrazolo[3,4-b]quinolines, pyrazolo[3,4-b][1,8]naphthyridines, benzo[e]pyrazolo[3,4-b]azepines, benzo[g]pyrazolo[3,4-b]azocines, pyrazolo[3,4-b]pyrido[3,2-g]azocines, and benzo[g]pyrazolo[3,4-b]azonines scaffolds were synthesized via a Friedel–Crafts cyclialkylation approach. The precursor acids were obtained by utilizing the modified Ullman coupling reactions of 5-chloro-3-methyl-1-phenyl-1H-pyrazole-4-carboxylic acid with different aryl amines followed by ring closures in the presence of AlCl3/CH3NO2 or P2O5 or polyphosphoric acid catalysts. Particular attention is given to the novel structures especially in regard to the promising pharmaceutical and therapeutic values associated with their skeletons.