Sulfonation, Sulfenylation, and Diazonium Coupling

Sulfenylation of A-methyl-2-thiomethylimidazole with trifluorometh-ylsulfenyl chloride in THF gives a 43% yield of the 4-trifluoromethylthio derivative (75JHC597). 

The reaction of aryldiazonium ions with l-(4 -sulfophenyl)-3-methyl-pyrazolium-5-one (7.70) takes place at the 4-position, and the p factor for the effects of substituents in the aryl ring of the diazo ion is 3.29, similar to that for coupling at the 1-position of 2-hydroxynaphthalene-6-sulfuric acid (69CCC3895). For coupling at the 4-position of l-phenyl-2,3-dimeth-ylpyrazolium-5-one (7.71) the corresponding p factor was 3.60 (69CC3905). 

Mercuriation of diphenyloxazoles occurs only in the heterocyclic rings. The order of reactivity, namely 2,4-diphenyl- 2,5-diphenyl- 4,5-di-phenyloxazole, suggests a positional reactivity order of 5 4 2 (66CHE14), though this conclusion is not rigorous because of the differential activating effects of the phenyl rings. 

Isoxazole decomposes under mercuriating conditions, though 3,5-di-substituted derivatives may be mercuriated in the 4-position in 90-100% yield (58ZOB359 60ZOB1269). 

From the ease of mercuriation of mono,- di-, and trimethylthiazoles, the positional reactivity order is indicated to be 5 4 2 (60CA24661c). Surprisingly, 2-acetamido-4-methylthiazole is said not to mercuriate (59JIC434), though the 5-position should be strongly activated it may be sterically hindered. Steric hindrance must be partly responsible for the reactivity order for substituted thiazoles 2-Ph- 4-Me-2-Ph- 2-Me-thiazole in this work the 4,5-dimethyl compound was unreactive [72CA(76)72617]. 

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