Cycloadditions benzene, sulfonyl

Homophthalic anhydrides can be prepared by the dehydration of homoph-thalic acid with add chloride, acid anhydride, phosgene, thionyl chloride, benzene sulfonyl chloride, ketene, phosphorous pentoxide, dicyclohexyl-carbodiimide, or J -carbonyldiimidazole. However, these methods are not always effective for the acid-sensitive and/or unreactive homophthaUc acid derivatives. We developed a very mild and efficient method for obtaining homophthaUc anhydrides using (trimethylsilyl)ethoxyacetylene [9] (Scheme 1). Thus the treatment of homophthaUc acid 1 with (trimethylsi-lyl)ethoxyacetylene 2 in inert solvents such as methylene chloride, 1,2-di-chloroethane, and acetonitrile gave the homophthaUc anhydride 3 in a quantitative yield accompanied by ethyl trimethylsilyl acetate as the only side product. The high purity homophthaUc anhydride 3 could be obtained for the next cycloaddition reaction just by evaporation to remove the reaction solvent and the formed ethyl trimethylsilyl acetate. The method is quite useful, and was also applicable to the syntheses of hetero-homophthalic anhydrides 4. 

TVA -Disulfonylsulfodiimides 244 react exothermically with butadiene to give 1-sulfo-nylimino-2-sulfonyl-3,6-dihydro-l,2-thiazines 245 (equation 130)121,122. IV-Aryl-AT-sul-fonylsulfodiimides 246 are much less reactive as dienophiles. The addition to butadiene to yield 247 takes place in boiling benzene (equation 131)123. No cycloaddition reactions of dialkyl- or diarylsulfodiimides are known. 

Amino-5-aryl-l,3,4-thiadiazole was treated with thionyl chloride in dry benzene to yield the N-sulfinylamine (93) an unstable compound, characterized by NMR and further derivatization. The sulfinylamine moiety caused an upheld shift on C(2) (4 6 ppm) comparable to a carbonyl or sulfonyl group, indicating the double-bond character of the N—S bond. Reaction of (93) with 2,3-dimethylbuta-1,3-diene yielded (94) via thermal cycloaddition <89JCS(P2)i855>. 

The conversion of 3-sulfolene to the useful sulfone (36) is itself an important procedure. A 1,3-dipolar cycloaddition of diazomethane to (36) was based on literature precedent for the formation of pyrazoles from sulfonyl alkenes and provided (37), from which benzene sulfonic acid was eliminated to give diazole (38) [17]. A mixture of products was obtained upon subsequent -substitution (Scheme 6.10). 

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