Benzimidazole oxidation

Hi) Transformation of benzofuroxans into quinoxaline and benzimidazole oxides... 

The second class of benzo-fused heterocycles accessible from benzofuroxans are benzimidazole oxides. In this case only one carbon from the co-reactant is incorporated in the product. With primary nitroalkanes 2-substituted l-hydroxybenzimidazole-3-oxides (46) are formed via displacement of nitrite, and / -sulfones behave similarly. The nitrile group of a-cyanoacetamides is likewise eliminated to alford 2-amide derivatives (46 R = CONRjX and the corresponding esters are formed in addition to the expected quinoxaline dioxides from acetoacetate esters. Under similar conditions secondary nitroalkyl compounds afford 2,2-disubstituted 2//-benzimidazole-1,3-dioxides (47). Benzimidazoles can also result from reaction of benzofuroxans with phosphorus ylides <86T3631>, nitrones (85H(23)1625>, and diazo compounds <75TL3577>. 

Acetylenic esters add to benzimidazole oxides which behave as 1,3-dipoles the reactions take place vigorously at room temperature. From l-methylbenzimidazole-3-oxide (408) and DMAD, Takahashi and Kano224 obtained 411 via the isoxazoline (409), whereas MP gave 412. The reaction of l,2-dimethylbenzimidazole-3-oxide (414) with DMAD the MP gave the benzimidazolium betaines 415 and 413 respectively ... 

The generation from furoxans of other heterocyclic systems, some of which show useful biological activity (see Section 4.22.5), has been the subject of intensive investigation. The following subsections summarize the conversion of benzofuroxans into quinoxaline and benzimidazole oxides, the rearrangement of 4-substituted benzofuroxans, and the transformation of monocyclic furoxans into isoxazoles and isoxazolines, furazans, and pyrazolines. More detailed discussion is to be found in recent comprehensive reviews (75S415, 76H(4)767, 81AHC(29)251>. 

In what appears to be a related reaction, benzimidazole oxides give rise to ben-zimidazolinones as by-products when treated with an acyl halide in the presence of alkali. With tosyl chloride the sole product is the benzimidazolinone (111) which may be formed as in Scheme 50. The C - N rearrangement could also take place via the oxaziridine (112) (73JCS(P1)70S). 

X - ray studies of initial and dyed by bis - (1 , 8 - naphthoilene - 1, 2 - benzimidazole) oxide (XLY) PCA studies have been carried out with the purpose of investigating possible changes in amorphous - crystalline stmcture of PCA fibre at the time of introducing such volumetric dyes as bis-aroilenbenzimidazoles and their distribution in the fibre. 

Less common methods of synthesis include nitrosation of suitable alkenes in acetonitrile solution (see Section 3.02.8.1.3(ii)) <84TLI319>, cyclization of iV-alkoxy ureas <87S1058>, and specific approaches to benzimidazole oxides from quinoxaline oxides, and to imidazole oxides from oxa-diazine and pyrazine oxides <93CHE127>. 

Benzofuroxans into Quinoxaline Oxides and Benzimidazole Oxides. . . 306... 

Transition-metal-catalyzed methods were utilized in the preparation of 2-substituted benzimidazoles. Oxidative C-H amination of arylamidines 64 provided access to 1,2-disubstituted benzimidazoles 65 in the presence of MCPBA as a terminal oxidant (130L1334). 1,2-Disubstituted benzimidazoles were synthesized using microwave-assisted solid phase with a phos-phonium linker (13JHC720). 

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