1,3-Benzoxathioles, formation

To a mixture of 3.2 g POC1, and 2.8 g N-methylformanilide that had been heated briefly on the steam bath (to the formation of a deep claret color) there was added 2.3 g 5-methoxy-l, 3-benzoxathiol, and steam hath heating was continued for an additional 5 min. The reaction mixture was poured into 100 mL H.O, and after a few minutes stirring, the insolubles changed to a loose solid. This was collected by filtration, H,0 washed and, after sucking as dry as possible, recrystallized from 30 mL boiling MeOH. This provided 1.9 g of 6-formy 1-5-methoxy-1,3-benzoxathiol as brownish needles that melted at 119-120 °C. 

Benzoxathiol-2-one formation can in turn be the desired reaction pathway. This compound can be similarly prepared when a methoxy group is present at the 2 position [67]. The cycUsation is carried out using hydroiodic acid or pyridine hydrochloride as demethylating agents (Scheme 25). 

Oxathians the formation of cyclic trithio-orthocarbonates (193) by the thermolysis of bis-(dithiocarbonates) the preparation of l,3-oxathiol-2-ones and of 2-substituted 1,3-oxathioles by treatment of moKlibromo-ketones with potassium ethyl xanthate a novel synthesis of 2/f-l,3-benzoxathiol-2-ones (194) by the HI- or pyridine-hydrochloride-induced cyclization of thiocarbamates and the base-catalysed cyclization and Smiles rearrangement of 3-(2,4,6-trinitrophenyl-thio)propanoI to give the benzoxathiepin (195). ... 

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