4.5- Diphenylimidazole. reaction with

Although not particularly well known, nitrosoimidazoles appear to be quite stable compounds. The nitroso function can be reduced to amino, or oxidized to nitro. When 5-nitroso-2,4-diphenylimidazole is subjected to dropwise treatment with phenylhydrazine there is some reduction, but ring modification with the formation of the oxadiazole (224) accompanies this reaction (Scheme 123) (60G831). The nitroso function is able to take part in condensation reactions with compounds which possess active methylene groups, and related species (B-76MI40701). 

Reactions of imidazoles with nucleophiles occur slowly as with thiazoles and demand vigorous conditions. Attack of the nucleophile occurs in the 2-position. For instance, l-methyl-4,5-diphenylimidazole reacts with potassium hydroxide at 300°C to give imidazol-2(3//)-one ... 

Diphenylimidazole-2-thiol 275 undergoes the Mannich reaction with aliphatic or aromatic amines and formaldehyde to furnish the corresponding thiadiazinoimidazole derivatives 276 in good yields. Likewise, 2-aryltriazole-... 

Whereas the cycloaddition of arylazirines with simple alkenes produces A -pyrrolines, a rearranged isomer can be formed when the alkene and the azirine moieties are suitably arranged in the same molecule. This type of intramolecular photocycloaddition was first detected using 2-vinyl-substituted azirines (75JA4682). Irradiation of azirine (54) in benzene afforded a 2,3-disubstituted pyrrole (55), while thermolysis gave a 2,5-disubstituted pyrrole (56). Photolysis of azirine (57) proceeded similarly and gave 1,2-diphenylimidazole (58) as the exclusive photoproduct. This stands in marked contrast to the thermal reaction of (57) which afforded 1,3-diphenylpyrazole (59) as the only product. 

Diphenylimidazole with palladium acetate forms the cyclometallated complex 80 (X = OAc) (97AOC491). The acetate group is replaced by chloride or bromide when 80 (X = OAc) reacts with sodium chloride or lithium bromide, respectively, to give 80 (X = C1, Br). Bromide with diethyl sulfide forms the mononuclear complex 81. Similar reactions are known for 1 -acetyl-2-phenylimidazole (96JOM(522)97). 1,5-Bis(A -methylimidazol-2-yl)pen-tane with palladium(II) acetate gives the cyclometallated complex 82 (OOJOM (607)194). 

The imidazo[ 1,2-b][l,2,4]triazino[5,6-6]indoles 597 were prepared by reacting 3-amino[l, 2,4]triazino[5,6-6]indole 592 with a-bromoketones 596. The structure was confirmed by the identity with the product of a reaction between isatin 599 or 2-phenylimino-3-oxoindole 600 and 1,2-diamino-4,5-diphenylimidazole 598 (82ZOR1272). Similarly, a cyclocondensation of 1,2-diamino-4-arylimidazoles with isatin and N-methylisatin was carried out (82KGS242). 

An unexpected one-pot two-step transformation of 3,4-diphenyl-l,2,5-thiadiazole 8 via the intermediate trimethylsi-lylmethylated 3,4-diphenyl-1,2,5-thiadiazolium triflate 20 gave the l-trimethylsilylmethyl-4,5-diphenylimidazole 139. The proposed reaction mechanism invokes desilylation of thiadiazolium 20 with CsF to afford the methide 138 (Scheme 21) <1999J(P1)1709>. 

The reaction of 4,5-diphenylimidazole-1,2-diamine 152 with substituted chalcones 153 in dimethylformamide for 1 h proceeds with the elimination of the hydrazine amino group, oxidation and formation of the appropriate 2,3,5,7-tetraaryl-5,6-dihydroimidazo[l,2-a]pyrimidin-6-ol 154 in low or moderate yields [126] (Scheme 4.47). The treatment of the same diamine with dibromo derivatives 155 produced imidazo[l,2-a]pyrimidines 156 [126]. 

Analogously, the reaction between phenylglyoxal, isobutylamine, n-butyl isocyanide, and benzoic acid afforded 3-oxo-3-phenylpropanoic amide 85 which was cy-clized to diphenylimidazol-5-carboxamide 86 in very high yield (Scheme 2.31) [60], The procedure was extended to solid-phase synthesis by employing resin-bound isocyanides. Wang resin was preferred to Rink resin because of its stability. The reaction of the resin-bound isocyanides 87 with supporting Ugi reagents afforded the... 

Diphenylimidazole is nitrated by nitric and sulfuric acids in the presence of urea to give 96% of 4,5-bis(4-nitrophenyl)imidazole [90GEP(O)3835195], whereas amyl nitrite reacts with 4,5-diphenylimida-zole to give 2-nitro-4,5-diphenylimidazole (42). This reaction may be re-... 

Diphenyl-4-nitrosoimidazole is oxidized by amyl nitrate to the corresponding 4-nitro derivative [592], An unusual reaction is observed when 4,5-diphenylim-idazole and 2-bromo-4,5-diphenylimidazole are boiled with amyl nitrite. Instead of nitrosation the substrate undergoes nitration with the formation of 2-nitro-4,5-di-phenylimidazole [593] (Scheme 115). 

It is a general rule that imidazoles and benzimidazoles are resistant to Friedel-Crafts reactions. This is not surprising since such basic compounds must be markedly deactivated in the presence of Lewis acids. Imidazolin-2-ones appear to be an exception and apparently possess sufficient activation to react. Reactions between imidazoles and Af-methylfor-manilide and phosphoryl chloride are also unproductive. With 4,5-diphenylimidazole, phenyl isocyanate at 80 °C gives products of both N- and C-substitution, but in boiling nitrobenzene only the latter (86) is formed. 2-Methyl-4-phenylimidazole gives (87) under the same conditions, and 1,3-diphenylimidazolium perchlorate is transformed by potassium t-butoxide into a ylide which reacts at C-2 with phenyl isothiocyanate. Sufficient activation is present in l-methyl-2-phenyl-4-phenylaminoimidazole for it to react by substitution at C-5 with acetic anhydride (71JOC3368). 

In the presence of potassium cyanide the N-methyl-C-phenylnitrone (112) takes part in yet a further cycloaddition reaction to give l-methyl-4,5-diphenylimidazole. With lithium metal the aldimine (113) forms a delocalized carbanion which will cyclize with aryl cyanides (Scheme 61) (80AHC(27)24l). See also Section 4.08.1.1.3. 

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