Oxidative imidazole

Similar reactions have been carried out with variously substituted pyrroline 1-oxides, imidazole 1-oxides, isoxazoline N-oxides (nitronic esters) and 3,4-diazacyclopentadienone AT-oxides in combination with a large variety of alkenic and alkynic dipolarophiles, aryl isocyanates, aryl isothiocyanates and N- sulfinylamines, leading to pyrrolidinoisoxazoles, pyrrolo[l,2-6][l,2,4]oxadiazoles, pyrrolo[2,l-d][l,2,3,5]oxathiadiazoles, isoxazolo[2,3-b ]isoxazoles and isoxazolo[l, 2-6 ]pyrazoles. 

The electrochemistry of a number of such six-coordinate compounds [MnXL]+ and seven-coordinate compounds [MX2L] (with L = (203), R,R = Me and X = halide, water, triphenylphosphine oxide, imidazole, 1-methylimidazole or pyridine) has been investigated.551 The redox behaviour of these compounds was of interest because it was considered that the potentially -acceptor macrocycle (203 R = R = Me) may promote the formation of Mn° or Mn1 species or may yield a metal-stabilized ligand radical with the manganese remaining in its divalent state. For a number of macrocyclic ligand systems, it has been demonstrated that the redox behaviour can be quite dependent on axial ligation it was also of interest to study whether this was the case for the present systems. 

Like other heterocyclic iV-oxides, imidazole 3-oxides 1063 react with AC2O to give the corresponding imidazolones 1064 and 1065 (Scheme 257). TMSCN transforms 1063 into imidazole 2-carbonitriles 1066, whereas alkyl thiones convert 1063 to 1067 <2000HCA728, 1998HCA1585, 2002AGE2290>. The 2-aminoimidazoles 1068, formed from the reactions with either isocyanate or isothiocyanate, react further with isocyanates to form ureas but are inert toward thiourea formation. In contrast to nonaromatic imidazole A -oxides (nitrones), oxides 1063 react with DMAD to form butanedioates 1069, rather than the (putative) [3-1-2] adduct <2000T5405>. 

Liu Y, Yu Q, Wu Y. More studies on the sulfonated poly(phenylene oxide)+imidazole bronsted acid-base polymer electrolyte membrane. J Phys Chem Solids 2007 68(2) 201-5. 

Dimerizations of p-Rich N-Heteroaromatic Compounds and Xanthine Derivatives. Sekine, Toshikazu Higuchi, Yoshihiro Yamada, Tomoko Murakoshi, Isamu (Fac. Pharm. Sci., Chiba Univ., Chiba, Japan 260). Chem. Pharm. BuU. 1989, 37 (8) 1987-9 (Eng.). N-Methylimidazole, benzimidazole, and N-methylbenzimidazole condensed dehydrogenatively to afford the corresponding sym. dimers when heated in the presence of Pd-Pt/C catalyst and pyridine N-oxide. Imidazole, pyrazole, and N-methylpyrazole did not dimerize under the same conditions. The same reactions using caffeine and 1,7-dimethylhypoxanthine gave the eorresponding dimers. 

Resorcinol or hydroquinone production from m- or -diisopropylben2ene [100-18-5] is realized in two steps, air oxidation and cleavage, as shown above. Air oxidation to obtain the dihydroperoxide (DHP) coproduces the corresponding hydroxyhydroperoxide (HHP) and dicarbinol (DC). This formation of alcohols is inherent to the autooxidation process itself and the amounts increase as DIPB conversion increases. Generally, this oxidation is carried out at 90—100°C in aqueous sodium hydroxide with eventually, in addition, organic bases (pyridine, imidazole, citrate, or oxalate) (8) as well as cobalt or copper salts (9). 

The pyrazole ring is resistant to oxidation and reduction. Only ozonolysis, electrolytic oxidations, or strong base can cause ring fission. On photolysis, pyrazoles undergo an unusual rearrangement to yield imidazoles via cleavage of the N —N2 bond, followed by cyclization of the radical iatermediate to azirine (27). 

Alloxan forms an oxime (1007) which is the same compound, violuric acid, as that formed by nitrosation of barbituric acid likewise, a hydrazone and semicarbazone. Reduction of alloxan gives first alloxantin, usually formulated as (1008), and then dialuric acid (1004 R = OH) the steps are reversible on oxidation. Vigorous oxidation with nitric acid and alkaline hydrolysis both give imidazole derivatives (parabanic acid and alloxanic acid, respectively) and thence aliphatic products. Alloxan and o-phenylenediamine give the benzopteridine, alloxazine (1009) (61MI21300). 

N-Unsubstituted pyrazoles and imidazoles add to unsaturated compounds in Michael reactions, for example acetylenecarboxylic esters and acrylonitrile readily form the expected addition products. Styrene oxide gives rise, for example, to 1-styrylimidazoles (76JCS(P1)545). Benzimidazole reacts with formaldehyde and secondary amines in the Mannich reaction to give 1-aminomethyl products. 

Imidazole rings also survive most oxidation conditions, but photosensitized oxidation of imidazoles can give diarylbenzamidines through a hydroperoxide (136) (70AHC(12)103). 

Alkyl radicals produced by oxidative decarboxylation of carboxylic acids are nucleophilic and attack protonated azoles at the most electron-deficient sites. Thus imidazole and 1-alkylimidazoles are alkylated exclusively at the 2-position (80AHC(27)241). Similarly, thiazoles are attacked in acidic media by methyl and propyl radicals to give 2-substituted derivatives in moderate yields, with smaller amounts of 5-substitution. These reactions have been reviewed (74AHC(i6)123) the mechanism involves an intermediate cr-complex. 

Alkylthio groups are oxidized to sulfoxides by H2O2 and readily by various oxidizing reagents to sulfones, e.g. in the imidazole series. The SR group is replaced by hydrogen with Raney nickel, and dealkylation is possible, e.g. of 3-alkylthio-l,2-dithiolyliums to give... 

As shown in Scheme 2, two heteroatom-carbon bonds are constructed in such a way that one component provides both heteroatoms for the resultant heterocycle. By variation of X and Z entry is readily obtained into thiazoles, oxazoles, imidazoles, etc. and by the use of the appropriate oxidation level in the carbonyl-containing component, further oxidized derivatives of these ring systems result. These processes are analogous to those utilized in the formation of five-membered heterocycles containing one heteroatom, involving cyclocondensation utilizing enols, enamines, etc. 

Isoxazole compounds can be converted into the corresponding isothiazoles by successive catalytic hydrogenation, sulfuration with phosphorus pentasulfide and oxidation with chloranil (72AHC(14)l, 75SST(3)541). 2,1-Benzisoxazoles give the 2,1-benzisothiazoles directly, by the action of phosphorus pentasulfide in either pyridine or molten imidazole (73SST(2)556, 77SST(4)339). (See also Chapter 4.16 for further discussion of these topics.)... 

Imidazole 1-oxide, l-methoxy-2,4,5-triphenyl-pK, 5, 384 B-76MI40701, 70AHC(12)103, 80AHC(27)241)... 

H-Imidazole 1-oxide, 2,4,4,5-tetramethyl- H NMR, 5, 16 <83UP40100> 4H-Imidazole-2,4,5-triamine, hexaethyl-... 

Imidazole, 4-acetyl-5-methyl-2-phenyl-synthesis, 5, 475 Imidazole, 1-acyl-reactions, 5, 452 rearrangement, 5, 379 Imidazole, 2-acyl-synthesis, 5, 392, 402, 408 Imidazole, 4-acyl-synthesis, 5, 468 Imidazole, C-acyl-UV spectra, 5, 356 Imidazole, N-acyl-hydrolysis rate constant, 5, 350 reactions, 5, 451-453 synthesis, 5, 54, 390-393 Imidazole, alkenyl-oxidation, 5, 437 polymerization, 5, 437 Imidazole, 1-alkoxycarbonyl-decarboxylation, 5, 453 Imidazole, 2-alkoxy-l-methyl-reactions, 5, 102 thermal rearrangement, 5, 443 Imidazole, 4-alkoxymethyl-synthesis, 5, 480 Imidazole, alkyl-oxidation, 5, 430 synthesis, 5, 484 UV spectra, 5, 355 Imidazole, 1-alkyl-alkylation, 5, 73 bromination, 5, 398, 399 HNMR, 5, 353 synthesis, 5, 383 thermal rearrangement, 5, 363 Imidazole, 2-alkyl-reactions, 5, 88 synthesis, 5, 469... 

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