Condensed thiophen ring systems. Part XIX. Synthesis of 6,7-dihydrothieno[3,2-c]pyridines and 4,5-dihydrothieno[2,3-c]pyridines by intramolecular cyclisation of 2-(2- or 3-thienyl)ethyl isothiocyanate

Abstract

Cyclisation of 2-(2-thienyl)ethyl isothiocyanate (8) with methyl fluorosulphate or triethyloxonium tetrafluoroborate gave 1-methylthio-(1) or 1-ethylthio-6,7-dihydrothieno[3,2-c]pyridine (2), respectively. Compound (1) was prepared also by cyclisation of the isothiocyanate (8) with polyphosphoric acid and subsequent alkylation of the 6,7-dihydrothieno[3,2-c]pyridine-4(5H)-thione (6) produced with methyl fluorosulphate. Compounds (5) and (7) were prepared similarly from 2-(3-thienyl)ethyl isothiocyanate (9). The amines (3) and (4) were prepared by reaction of compound (1) or (2) with the appropriate aliphatic amine.