Some polycyclic systems related to [1]benzothieno[2,3-c]pyridine

Abstract

3,4-Dihydro[1]benzothieno[2,3-c]pyridin-1(2H)-one (2) has been prepared by Bischler–Napieralski cyclisation of N-ethoxycarbonyl-2-(3-benzo[b]thienyl)ethylamine (4) and by Beckmann rearrangement of the mixture of stereoisomeric oximes from 1,2-dihydrocyclopenta[b][1]benzothiophen-3-one (5). It condensed with methyl anthranilate to give the sulphur analogue (1) of rutecarpine.Oxidation of N-2-(3-benzo[b]thienyl)ethylpiperidine (13) with mercury(II) acetate gave a tetracyclic product (6); a related compound (7) was obtained by partial catalytic reduction of 3-acetyl-N-2-(3-benzo[b]thienyl)-ethylpyridinium bromide (10) and treatment of the resulting 5-acetyl-N-2-(3-benzo[b]thienyl)ethyl-1,2,3,4-tetrahydropyridine (15) with hydrochloric acid. Reduction (LiAlH4) of N-2-(3-benzo[b]thienyl)ethylpyridinium bromide (8) took place only in the pyridine ring, and did not lead to tetracyclic products.