Friedel–Crafts Chemistry. Part 39. Unprecedented Facile Route to the Synthesis of Benzo[b][1]benzazepines via Intramolecular Friedel–Crafts Cyclialkylations

A series of six pharmaceutically promising 5,6-dihydro-11H-benzo[b][1]benzazepine derivatives (1c–h) were cleanly prepared by Friedel–Crafts cyclialkylations of nitrogen-containing alkanols in the presence of AlCl3, 85 % H2SO4 or polyphosphoric acid catalysts. The precursor alkanols (13a–f) were readily prepared by reaction of two synthesized carboxylic acid esters (12a, b) with different Grignard reagents. Also, two dibenzo[b,f]azepinones (15a, b) were prepared by Friedel–Crafts cycliacylation and reduced to the corresponding 5,6-dihydro-11H-benzo[b][1]benzazepines (1a, b). Overall, this approach allows easy and efficient access to polytricyclic amines from easily synthesized alkanols or cycloketones. A plausible carbocation mechanism is proposed to account for the results.