Synthesis of angular-substituted tetracyclic azepino-indole derivatives via N-acyliminium ion cyclization

A concise and efficient synthesis of tetracyclic azepino-indole derivatives 2 having a substituent at the angular position has been accomplished throu gh an N-acyliminium ion cyclization. The coupling reaction of indol-3-yl-et hylamine 3 with 4- or 5-keto-acid 4 followed by cyclization reaction of the resulting tautomeric mixtures of keto-amide 5 and hydroxylactam 6 in reflu xing formic acid provided 2. (C) 1999 Elsevier Science Ltd. All rights rese rved.