Sulfur Dioxide and Sulfite Esters

The reversible reaction between butadiene and sulfur dioxide, which yields sulfolene, has been known for a long time. Such cycloaddition reactions of sulfur dioxide, and of other sulfur oxides, have been reviewed by Block.49 

Reactions of Organosulfur Compounds, p. 268. Academic Press, New York, 1978. 

Smirnov-Zamkov et al. have shown that sulfur dioxide and hydrogen bromide react with alkynes with phenylacetylene derivatives, such as the sulfonamide (42), a benzo[b]thiophene (43) is formed.50 The mixture of sulfur dioxide and hydrogen bromide appears to behave like thionyl bromide, cf. thionyl chloride (see Section V,B). 

Sulfur dioxide has long been used in an industrial synthesis of isothiazole from propene, sulfur dioxide, and ammonia over a catalyst at 200°C.51 

In a remarkable reaction, the anion of phenylacetonitrile was found to react with dialkyl sulfites to give 4,5-diphenylisothiazol-3-ol (44) in moderate 

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