Intramolecular cyclisation of arylalkyl isothiocyanates. Part 3. Synthesis of 4,5-dihydro-3H-2-benzazepines and 7,8-dihydro-6H-thieno[3,2-c]-azepines

Abstract

The 4,5-dihydro-3H-benzazepine-1-thiones (6) and (7), prepared by cyclisation of 3-phenylpropyl isothiocyanate (2) and its 3,4-dimethoxy-derivative (3) with polyphosphoric acid or aluminium chloride, were alkylated with tri-ethyloxonium tetrafluoroborate, dimethyl sulphate, or methyl fluorosulphate to yield the 1-alkylthio-compounds (8)–(10). 3-(2-Thienyl)propyl isothiocyanate (12) reacted with polyphosphoric acid to give a thione (13) which was prepared also from the corresponding lactam (14) and phosphorus pentasulphide. The thione (13) and the lactam (14) were ethylated with triethyloxonium tetrafluoroborate and each of the products. (15) and (16), respectively, was converted into 4-cyclopropylamino-7,8-dihydro-6H-thieno[3,2-c]azepine (17) by reaction with cyclopropylamine. With aluminium chloride 3-(2-thienyl)propyl isothiocyanate (12) gave a product (18) arising from intermolecular condensation. Attempts to cyclise the isothiocyanates (1)–(5), (12), (26), and (29) with triethyloxonium tetrafluoroborate succeeded only in the case of compound (3), which gave 1-ethylthio-4,5-dihydro-7,8-dimethoxy-3H-2-benzazepine (10).