Imidazoline 1,3-dioxide

Hydroxyimidazole 1-oxides 323 react with dibenzoylperoxide furnishing imidazoline 1,3-dioxide 324 (1971Z62,1993CHE127) (Scheme 97). 

On studying electrochemical properties of l-hydroxy-3-imidazoline-3-oxides and their conversion into nitronyl nitroxyl radicals (NNR), the intermediate production of a nonaromatic radical cation (220) of AH -imidazole-1,3- dioxides (219) (Scheme 2.78) (101) was suggested. 

Owing to the existence of two centers for nucleophilic attack (at C2 and C5) in radical cations (220) obtained from the oxidation of 4-H -imidazole-1,3-dioxides (219), the formation of two products of methoxy group addition was observed, namely NNR (221) and NR of 3-imidazoline-3-oxide (222). The ratio of the products depends on the electronic nature of substitutes R1 and R2. Both, the donor character of R1 and acceptor character of R2 facilitate the formation of nitroxyl radicals (222) with the yield of (221) increasing with the inverted effect of the substituents. As was mentioned in Section 2.4, the results of preparative electrochemical oxidative methoxylation of 4H -imidazole-1,3-dioxides are similar to the results of chemical oxidation. 

Oxidative Fluorination of Nitrones to a-Fluorosubstituted Nitroxyl Radicals Formation of nitroxyl radicals by the radical cation route was observed in reactions of various nitrones with xenon difluoride in dry methylene chloride (520, 523). In this reaction, more than 40 nitrones, including 4H -imidazole N,N -dioxides (219), 4H -imidazole TV-oxides (223) and (224), 2H -imidazole N -oxides (225), 2H -imidazole TV,TV-dioxides (226), 3,3,5,5-tetramethylpyrroline N -oxide (TMPO), derivatives of 3-imidazoline-3-oxides (231) and (232), have been examined. ESR spectra of nitroxyl radicals containing one or two fluorine atoms at a-C have been registered (Scheme 2.108) (523). In the case of... 

A recent report shows that 1,2,3,4-benzotetrazine 1,3-dioxide nitroderivatives 73 (R=N O2) are thiol dependent N O-donors and potent activators of the sGC [73]. Activation of the sGC was inhibited in the presence either of ODQ or of the N O scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethy]imidazoline-l-oxyl-3-oxide (carboxy-PTIO). All products inhibited A DP-induced aggregation of human platelets, with the potency sequence 7-nitro >5,7-dinitro >5-nitro. 

Chloride dioxide (CIO2) forms red charge-transfer complexes with piperidine and imidazoline nitroxyl radicals that slowly transform into oxoammonium salts. ... 

Sodium borohydride converts 4//-imidazole N-oxides into 1-hydroxy-imidazoline or -imidazolidine derivatives. Under the same conditions 1,3-dioxides form 1,3-dihydroxy-imidazolidines (76CHE1280). 

When l-hydroxy-3-imidazoline 3-oxides (263) are treated with HCl they dehydrate forming imidazole 3-oxides (Scheme 153) (73CHE1175). Reduction of 4//-imidazole N-oxides with borohydride leads to either 1-hydroxy-imidazolines or -imidazolidines, depending on the position of the oxide function. Under the same conditions 4//-imidazole 1,3-dioxides give 1,3-dihydroxyimidazolidines (76CHE1280). The 4iT-imidazole AT-oxides are prepared by heating 5,5-disubstituted l-acyloxy-3-imidazoline 3-oxides in vacuo. 

The specific synthesis of 1,4- and 1,5-disubstituted imidazoles in 70% yields has been achieved by cyclizing 2-amino-3-methylaminopropionic acid with triethyl orthoformate. The products are isolated after dehydrogenation with active manganese dioxide of the 2-imidazoline (69 Scheme 37) (70AHC(12)103). 

Cyclohexanedione- and cycloheptanedione-l,2-dioximes react with ketones in acid medium to give 2f/-imidazole 1,3-dioxides a-aminooximes give 3-imidazoline 3-oxides under similar conditions (Scheme 50) (80CHE628). 

A specific synthesis of 1,4- and 1,5-disubstituted imidazoles has been accomplished in about 70% yields by cyclization of 2-amino-3-methylaminopropanoic acid and 3-amino-2-methylaminopropanoic acid, respectively, with tricthyl orthoformate (Scheme 3.1.2). The initial product is the 2-imidazoline, which needs to be aromatized by treatment with active manganese dioxide [10]. 

To a solution of the imidazoline (7.5 g) in chloroform (150 ml) is added active manganese dioxide (30 g). The suspension is stirred at room temperature (16 h) then filtered, and the solid washed with hot chloroform. Evaporation of the combined chloroform fractions gives the imidazole ester (5.2 g). Sublimation at 80°C (0.05 mmHg) gives the pure product, m.p. 97-98°C. 

The isomeric 1-suhstituted imidazole-5-carboxylates are made by cyclization of 3-amino-2-alkylaminopropanoic acids with triethyl orthoformate followed by active manganese dioxide oxidation of the imidazoline product (see Section 3.1.1), or from IV-substituted glycine esters, which are formylated, converted into the enolates and then condensed with potassium thiocyanate... 

Althiophene 1,1-dioxide, which was reported years ago,118 has recently been reinvestigated,125,126 It was found that the anti head-to-head (119) and anti head-to-tail (120) isomers are formed in a ratio of 2.7. This dimerization was proposed to occur via attack of a molecule in the excited triplet state (Er SO kcal/mol) on another molecule in the ground state. The preferential formation of isomer 119 was attributed to a better stabilization of the more polar transition state in the formation of 119 relative to 120 in view of the observed effect of the polarity of the solvent on the ratio of 119 to 120. Similar dimerizations have been reported for 2-nitrobenzo-l,4-dithiin (121)127 and 1,1-dimethyl-2,5-diphenyl-l-silacyclopenta-2,4-diene (111).128 Other heterocycles that dimerize via (2 + 2)-cycloaddition, either upon direct or upon sensitized irradiation, are l/f-dibenzo[6,/l-azepine derivatives (122),129 vinylene carbonates (123),u,no and 1,3-substituted imidazolin-2-ones (124).,3, ,2... 

Biimidazole (3). 2,2 -Bi(2-imidazoline) (1) can be oxidized to 2,2 -biimidazole (3) by conversion to the bistrimethylsilyl derivative (2), which is soluble in organic solvents, and oxidation of (2) in CCI4 with the activated manganese dioxide of Goldman (2, 257). The procedure can also be used to oxidize 2-methyl-2-imidazoline to 2-methylimidazole (67% overall yield). ... 

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