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Pentane-2.4-dione reacts with 3-chloro-I ,2-benzisothiazole in the presence of sodium ethoxide to form 2-acetyl-3-aminobenzo [b] thiophen. Under similar conditions, ethyl acetoacetate and diethyl malonate each give mainly ethyl 3-aminobenzo[b]thiophen-2-carboxylate. Under slightly modified conditions diethyl malonate gives, in addition, some of the expected diethyl (1.2-benzisothiazol-3-yl) malonate, whereas ethyl cyanoacetate forms only ethyl (1,2-benzisothiazol-3-yl)cyanoacetate irrespective of conditions. A mechanism is suggested involving S-substituted o-cyanothiophenols as possible intermediates in those reactions which lead to benzo[b]thiophen derivatives. Support for this mechanism comes from the reaction of o-cyanothiophenol in aqueous sodium hydroxide with ethyl bromoacetate, chloroacetone, phenacyl chloride, chloroacetonitrile, or bromonitromethane to give respectively 2-ethoxycarbonyl-, 2-acetyl-, 2-benzoyl-, 2-cyano-, and 2-nitro-3-aminobenzo[b] thiophen.

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Hull HU6 7RXEthyl (1.2-benzisothiazol-3-y1)cyanoacetate exists as a mixture of two tautomers which decomposes to (1 ,Z-benzisothiazol-3-y1)acetonitrile (85%) when heated in dimethyl sulphoxide. Treatment of diethyl (1 2-benzisothiazol-3-yl)malonate with ethanolic sodium ethoxide gives ethyl (1.2-benzisothiazol-3-yl)acetate, which affords 3-methyl-1.2-benzisothiazole on successive hydrolysis and decarboxylation. The methyl group in 3-methyl-1.2-benzisothiazole is resistant to oxidation. Attempted Vilsmeier-Haack formylation of 3-methyl-1.2-benzisothiazole with dimethylformamide and phosphoryl chloride gives a mixture of N2-In contrast, 2-methylbenzothiazole gives (benzothiazol-2-yl) malonaldehyde or a related enamine.

Das Benzisothiazol (I) reagiert mit NaCN in wäßrigem Aceton zum Thiocyanat (II) (62% Ausbeute), zum Disulfid (III) (22%) und zum Benzothiophen (IV) (6%).