2.1- Benzisothiazolium salts, synthesis

Another general new route for the synthesis of 2-aryl-1,2-benzisothiazolium salts 117a-i consists of cyclocondensation via 116, which were easily generated by reaction of the 2-thiocyanatobenzaldehyde 118 with different anilines (05UP1, Scheme 39). 

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. 

Benzisothiazolium salts are hydrolysed to ort/zo-aminobenzaldehydes their use as synthons for such aldehydes is illustrated by the quinolone synthesis below. 

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