Synthesis of tetracyclic dibenzo[c,f]azepine and benzo[f]thieno[3,2-c]azepine derivatives via N-acyliminium ion cyclization

Abstract

Tetracyclic dibenzo[c,f]-4-oxopyrrolo[1,2-c]azepine (2a), dibenzo[c,f]-5-oxopiperido[1,2-c]azepine (2b), benzo[f]-4-oxopyrrolo[1,2-a]thieno[3,2-c]azepine (2c), and benzo[f]-5-oxopiperido[1,2-a]thieno[3,2-c]azepine (2d) were prepared through intramolecular N-acyliminium ion cyclization of hydroxylactams (3a-d) with aromatic or heteroaromatic rings such as benzene and thiophene as a pi -nucleophile. In the case of furan ring, the hydroxylactams (3e, f) were completely decomposed under the acidic conditions (formic acid or methanesulfonic acid). Subsequent reduction of 2a-d with BF3.O(C2H5)(2) and BH3.S(CH3)(2) finally provided the tetracyclic dibenzo[c,f]pyrrolo[1,2-c]azepine (1a), dibenzo[c,f]piperido[1,2-c]azepine (1b), benzo[f]pyrrolo[1,2-a]thieno[3,2-c]azepine (1c), and benzo[f]piperido[1,2-a]thieno[3,2-c]azepine derivatives (1d) as analogues of mianserin.