Hydrogen Peroxide reaction with thiophene

Oxidation of thiophene with Fenton-like reagents produces 2-hydroxythiophene of which the 2(570 One isomer is the most stable (Eq. 1) <96JCR(S)242>. In contrast, methyltrioxorhenium (Vn) catalyzed hydrogen peroxide oxidation of thiophene and its derivatives forms first the sulfoxide and ultimately the sulfone derivatives <96107211>. Anodic oxidation of aminated dibenzothiophene produces stable radical cation salts <96BSF597>. Reduction of dihalothiophene at carbon cathodes produces the first example of an electrochemical halogen dance reaction (Eq. 2) <96JOC8074>. 

Nonaflnoro-4-iodobntane can serve as a source of nonafluorbutyl radical under oxidative conditions. The reaction with thiophene 1 was carried out under reflux in AcOH in the presence of hydrogen peroxide and benzoyl peroxide. Other solvents appeared to be less effective, probably because hydrogen abstraction from the solvent by nonaflnorbntyl radical competes with the attack of thiophene [49]. 

This gives tautomeric mixtures119 when the tert-butyl group is removed. The methyl ether has been used to obtain 3-hydroxy-2-carbonyl derivatives in the selenophene series.120 The unsubstituted 2-hydroxyselenophene system has been prepared by hydrogen peroxide oxidation of 2-selenophene-boronic acid.121 However, in the 5-methyl-substituted system deboronation became such an important side reaction that 5-methyl-2-hydroxyselenophene had to be prepared by acid-catalyzed dealkylation of 5-methyl-2-fert-butoxy-selenophene. Both 2-hydroxy- and 5-methyl-2-hydroxyselenophene exist mainly as 3-selenolene-2-ones (93) and for the 5-methyl derivative it was possible to isolate the / ,y-unsaturated form (92) and follow the tautomeric isomerization. The activation parameters thus obtained were compared with those for the corresponding furan and thiophene systems. 

Thiophene sulfoxides and thiophene sulfones can be prepared by direct oxidation of the corresponding sulfides (Section 3.15.9.5.1) with hydrogen peroxide. 2-Thiophene sulfones are also prepared by reaction of arylsulfonyl chlorides with thiophene under mild Friedel-Crafts conditions, or by condensation of 2-thiophenesulfonyl chlorides with aromatic compounds (Section 3.14.2.4). 

The reaction of (148) with glycol and hydrogen peroxide gave (149). Compound (19b) has been reduced with liAlH4 to the corresponding alcohol, which was converted into the aldehyde and bromomethyl and aminomethyl derivatives that are of pharmaceutical interest. A mild method for the hydrolysis and decarboxylation of various amides of methyl 3-aminothiophen-2-carboxylates has been developed. Thermal decomposition of (150) led to cleavage of the thiophen ring, with extrusion of sulphur and formation of the isothiazole (151). ... 

Perflnoroalkylation is often performed with bis(perfluoralkanoyl)peroxides, e.g. bis(triflnoroacetyl)peroxide and bis(heptafluorobutyryl)peroxide, which are thermally stable, convenient to nse, and can be obtained from the corresponding anhydrides and hydrogen peroxide in Freon 113 (CFCI2CF2CI) as a solvent. Perfluorooxaalkanoylperoxides provide the same reactivity. The mechanism of the transformation inclndes oxidation of thiophene to radical cation, followed by reaction with perflnoro radical to produce 2-perfluoroalkylthiophenes [50],... 

These results show that in the phenylation of thiazole with benzoyl peroxide two secondary reactions enter in competition the attack of thiazole by benzoyloxy radicals, leading to a mixture of thiazolyl benzoates, and the formation of dithiazolyle through attack of thiazole by the thiazolyl radicals resulting from hydrogen abstraction on the substrate and from the dimerization of these radicals. This last reaction is less important than in the case of thiophene but more important than in the case of pyridine (398). 

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