Application of 7-endo-trig Pictet-Spengler Cyclization to the Formation of the Benzazepine Ring: Synthesis of Benzazepinoindoles

The preparation of benzazepinoindoles, fused heterocycles with a benzazepine moiety, was accomplished through an intramolecular 7-endo-trig Pictet-Spengler cyclization. The precursors comprising C-3- or C-2-linked o-aminobenzylindoles required for the cyclization were obtained either by treating indoles with o-nitrobenzyl bromide followed by reduction of the nitro group or by treating 2-nitrophenylacetic acid with DCC/DMAP followed by reduction of the aryl nitro functionality. Resulting substrates 5 and 6 were then subjected to the 7-endo-trig Pictet-Spengler reaction with a variety of aldehydes and ketones to furnish new polycyclic structures benzazepinoindoles. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)