Oxidation of heterocycles

Arene oxides of heterocycles such as pyridine have often been postulated as photoisomerization intermediates (81H(15)1569,72JOC3592) but to date they have not been isolated or extensively studied. 

Selective oxidation of heterocycles catalyzed by peroxidases 97T13183. 

Oxidation of heterocyclic aromatic amines, N-oxide reduction... 

Three short sections complete this chapter. In Sect. 5.3, we examine the metabolism of nonantibiotic lactams of medicinal or toxicological interest. Sect. 5.4 is concerned with complex lactams defined as containing one or more additional heteroatoms in the ring. Finally, we will discuss in Sect. 5.5 the fate of lactams generated as metabolites by the oxidation of heterocycles containing a N-atom. 

The presence of electron-donating substituents generally favors oxidation of heterocycles. 

Oxidations of heterocycles can afford formations of double bonds. This is illustrated by the anodic oxidation of dihydropy-ridines (Scheme 11) [16] for which pyri-dinium cations are produced according to an ECE mechanism. Unsubstituted dihy-dropyridines at carbon 4 give pyridines. 

Table 6.10. Half-wave potentials for the oxidation of heterocycles 68 at a rotating platinum anode in acetonitiile, lithium perchlorate [231].]...

D. Model Studies on Enzymatic Oxidation of Heterocycles and Aromatic... 

Anodic oxidation of heterocyclic thiones leads generally to disulfides. Thus cyclic voltammetric data at a pyrolytic graphite anode of purine-2,6-dithione show three peaks. The first and second correspond to a disulfide formation from the 6- and 2-thione groups, respectively, whereas the third is due to an oxidation to purine-2,6-disulfonic acid.432 Similarly, the electrochemical oxidation of benzthiazole-2-thione and benzimidazole-2-thione in CH3CN-NaC104 at a platinum electrode afforded the corresponding disulfides in good yield.433... 

Photo-oxidation of heterocycles leads to unstable endoperoxides whose existence has been generally proven by low temperature NMR. In addition to the classical transformations of peroxides (reduction, hydrolysis, deoxygenation, generally performed at low temperature), the bicyclic peroxides from heterocycles can afford characteristic rearranged products... 

It is possible to speed up aliphatic tertiary amine oxidation by adding tungstate or molybdate catalysts.334 However, for oxidation of aromatic and particularly heterocyclic tertiary nitrogen, a stronger system than hydrogen peroxide alone is required. iV-Oxidation of heterocycles is of pivotal importance in industrial chemical synthesis.335 Catalysed systems have been applied and these are dominated by metal peroxo systems based on molybdenum or tungsten. For example, quinoxaline and pyrazine may be oxidized to mono- or... 

Chromic acid is particularly useful for the oxidation of heterocyclic boranes which are resistant to oxidation by the usual oxidants (Na0H/H202 R3NO O2), e.g. equation (46). ... 

The oxidation of heterocyclic compounds functions in the. same way mechanistically as for carbocycles. Substituents at the C = C bond are eliminated during the reaction and the heteroatoms do not seem to have an influence on the mechanism of the reaction. 

Vanadium catalysts for oxidation of heterocyclic compounds 90MI3. 

The peracid is prepared in 65-75 % yield by the reaction between o-sulfobenzoic anhydride and 30% hydrogen peroxide in acetone solution at —4 to 0°C. The solution is used directly for epoxidation of olefins. Since the reagent contains a strongly acidic group, the initially formed epoxide undergoes acid cleavage to a truns-diol unless a solid buffer such as sodium carbonate is present. The peracid can also be used for Baeyer-Villigcr oxidation and for oxidation of heterocyclic t-amines to N-oxides. ... 

A formal hydration of 241 at X, only possible for X = S or Se, yields the corresponding sulfoxide (e.g., 247) or selenoxide of the heterocycle. No radicals have been substantiated, in the writer s view, which arise by further oxidation of heterocycles with oxidized group VI heteroatoms. 

Oxidation of heterocyclic compounds with permanganate anion 04KGS643. 

Polyvalent iodine compounds in the oxidation of heterocycles 02CRV2523. 

Benzylic oxidation of heterocycles with quinones 80YGK1163. Diazotization of heteroaromatic amines 83UK777. 

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