Ring transformations of 2-hydroxy-(4-chloro-5H-1,2,3-dithiazol-5-ylideneamino)arenes

The cyclisation reactions of 2-(4-chloro-5H-1,2,3-dithiazol-5-ylidene-amino)phenol (5a), 3-(4-chloro-5H-1,2,3-dithiazol-5-ylideneamino)pyridin-2-ol (5b) and 2-(4-chloro-5H-1,2,3-dithiazol-5-ylideneamino)pyridin-3-ol (5c) are investigated. Thermolysis in hot PhCl (132 °C) or under solvent free conditions at ca. 200 °C gave benzo[d]oxazole-2-carbonitrile (4a), oxazolo[5,4-b]pyridine-2-carbonitrile (4b) and oxazolo[4,5-b]pyridine-2-carbonitrile (4c) in high yields, while treatment with either NaH in dry THF at 66 °C or with i-Pr2NEt in DCM at 20 °C gave benzo[b][1,2,3]dithiazolo[5,4-e][1,4]oxazine (6a), [1,2,3]dithiazolo[5,4-e]pyrido[2,3-b][1,4]oxazine (6b) and oxazolo[4,5-b]pyridine (4c), respectively. The transformation of benzoxazine 6a and the pyridoxazine 6b into the corresponding oxazoles 4a and 4b was also investigated, and tentative mechanistic pathways for these transformations are proposed.

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