Isothiazoles from bicyclic systems

Bicyclic isothiazole dioxides 81 (99JHC(36)161), on treatment with Ai-nucleo-philes such as benzylamine, afforded isothiazole dioxides 82a,b together with a minor amount of compounds 83. Alternatively, 82b could be obtained from 84 by reduction with 1,2-dimethylhydrazine and DBU. By using r-butylamine as the A-nucleophile, due to steric reasons, the formation of the isothiazole dioxide 85 could also be observed followed by transformation in the bicyclic system 86. 

The 1,3-dipolar cycloaddition of diazoalkanes 276 and nitrile oxides 279 to isothiazole dioxides 275 provides an easy entry into fused bicyclic isothiazole systems 277 and 280, respectively <06JHC1045>. The adducts from 4-bromoisothiazole (R1 = Br) are labile and undergo spontaneous debromination to form the aromatic bicyclic pyrazolo-isothiazoles 278... 

Isothiazolo[5,l-e]isothiazoles.—A multi-stage synthesis of 1,3,4,6-tetra-methylisothiazolo[5,l-e]isothiazole (173) from 3-ethyl-4-methyl-l,2-di-thiolium perchlorate (172) has been briefly mentioned. The product is of especial interest in that it may be formulated as the bicyclic structure (173), or as a system of rapidly interconverting valence isomers (174) and... 

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