Regioselective hydrodehalogenation of 3,5-dihaloisothiazole-4-carbonitriles: synthesis of 3-haloisothiazole-4-carbonitriles

3,5-Dibromoisothiazole-4-carbonitrile 1 treated with Zn or In dust (5 equiv) and HCO2H undergoes regioselective hydrodebromination to give 3-bromoisothiazole-4-carbonitrile 3 in 70–74% yield. Similarly, 5-bromo and iodo 3-chloroisothiazole-4-carbonitriles 8 and 9 give 3-chloroisothiazole-4-carbonitrile 4 in 77 and 85% yields, respectively. Also hydrodeamination of 5-amino-3-chloroisothiazole-4-carbonitrile 7 using isoamyl nitrite gives the latter in 95% yield. The dibromoisothiazole 1 reacts with Zn dust in either DCO2D or HCO2D to give 3-bromo-5-deuterioisothiazole-4-carbonitrile 10 in 71 and 58% yields, respectively. The 3-bromoisothiazole 3 reacts with cyclic dialkylamines to give the corresponding 2-(dialkylaminomethylene)-malononitriles and not the expected 3-dialkylaminoisothiazole-4-carbonitriles. Finally, the 3-bromoisothiazole 3 is readily converted into both 3-bromoisothiazole-4-carboxamide 19 and the carboxylic acid 20. All products are fully characterized.

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