Conversions of thiochroman-4-ones into 1,2-benzothiazepine, benzo-[b]thiophen, and 1,2-benzisothiazole systems via sulphimide intermediates

Abstract

Reaction of thiochroman-4-ones (1a–g) with chloramine-T gave the corresponding N-tosylsulphimides (2a–g) and sulphoxides (5a–g). The N-tosylsulphimides (2a–d), on reaction with triethylamine in chloroform, gave 2-tosyl-2,3-dihydro-1,2-benzothiazepin-5(4H)-ones (3a–d), but the 2-methyl congeners (2e and f) yielded 2-crotonoyl-N-tosylbenzenesulphenamides (4e and f). When the reaction was carried out in acetonitrile, (2e and f) afforded (3e and f) and (Z)-2-ethylidene-2,3-dihydrobenzo [b]thiophen-3(2H)-ones (7e and f). The 2,2-dimethyl derivative (2g) led to only (4g) and (7g). Heating (2a–c) in acetic acid gave Diels–Alder dimers (6a–c) of 2-methylidene-2,3-dihydrobenzo [b]thiophen-3-ones, and (2e–g), upon heating in chloroform containing acetic acid, gave (7e–g). S-Amination of (1a, b, and d–f) with O-mesitylenesulphonylhydroxylamine followed by alkaline treatment gave 3-vinyl-1,2-benzisothiazoles (11a, b, and d–f).