Indoles XIV. 4-phenylpyrido[4,3-b]indoles and 5-phenylazepino[4,5-b]indoles by cyclisation of N-indolylalkylephedrine derivatives - Scope and stereoselectivity

4-Phenyltetrahydropyrido[4,3-b]indoles (1) and 5-phenylhexahydroazepino[4,5 -b]indoles (2) were obtained by cyclisation reactions starting from N-3-ind olylmethylephedrines and N-3-indolylethylnorephedrines respectively, using conc. sulfuric acid (for 1) and PPA (for 2), the latter cyclisation yieldin g to the racemised azepinoindoles (2), whereas the previous one reacts to I in a remarkably stereoselective manner with double inversion = retention o f its configuration, obviously going through a spirocyclic intermediate.