2- Alkyl-1,2-benzisothiazol-3 -thiones

The general synthesis of 2,1-benzisothiazolium salts consists mainly in the N-alkylation of the corresponding 2,1-benzisothiazole as well in the S-alkylation of 2,1 -benzisothiazol-3(2//)-ones and thiones as well as in O/S-elimination. 

A-Aryl 3-chloro-l,2-benzisothiazolium chlorides 109 were converted with thio-acetic acid to 3-aryl-imino-l,2-benzdithioles 332. In contrast, N-alkyl salts 109 reacted to form 2-alkyl-l,2-benzisothiazol-3(2//)-thiones 161, which are in equilibrium with 332 (67CB2435, Scheme 110). 

Benzisothiazole and its derivatives readily form quaternary salts on treatment with alkyl or benzyl halides. These salts (86) are useful synthetic intermediates the reactions they undergo are summarized in Scheme 2. The products include 2,1-benzisothiazolines,96 quinolones,122,123 benzodiazepi-nones (including a one-step synthesis of the tranquilizer Valium),96 124 o-aminobenzaldehydes and o-aminoaryl ketones,122,125 2,1-benzisothiazole-3-thiones,122 and cyanine dyes,126 the latter resulting from the activation of the methyl group in the 3-position of the quaternary salt (86, R = R = Me). 

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