2H-Imidazoles

Migrations of C- linked substituents around the ring, on to carbon or nitrogen atoms, are common amongst these compounds. This is the van Alphen-Huttel rearrangement and by it 3H-pyrazoles are converted into 1//-pyrazoles, and 2H-imidazoles are thermally iso-merized into IH-imidazoles. 

Imidazole, 2,4,5-triphenyl-dipole moment, 5, 351 (71CHE801) 2H-Imidazole, 2,2-dimethyl-4-phenyl- H NMR, 5, 16 (83UP40100)... 

Auch in Dibenzofulven-Derivaten wird die semicyclische C=C-Doppelbindung durch Diboran unmittelbar abgesattigt9 in 2-Diphenylmethylen-2H-imidazol kann sie bereits mit Natriumboranat in Athanol gesattigt werden10. 

The reaction of 1-amino-1-deoxyketoses, and their N-alkyl and N-aryl derivatives, with alkyl or aryl isothiocyanates (Huber et al, 1960) was studied in more detail, and new 4-(alditol-l-yl)-l-alkyl(aryl)-3-alkyl(aryl)-l,3-dihydro-2H-imidazole-2-thiones were obtained. These compounds were used as starting materials for the synthesis of OL-histidines, DL-histidine-2-thiol, and other imidazole derivatives of biological interest. 

A. 2,2-Spirocyclohexane-4,5-diphenyl-2H-imidazole (Note 1). A 2-L, threenecked, round-bottomed flask equipped with a mechanical stirrer and a reflux condenser is charged with 1.0 L of glacial acetic acid (Note 2), 158 g (0.75 mol) of... 

Condensation of hydroxyamino-ketones (166) with ketones and ammonium acetate leads to the formation of 2H -imidazole-1 -oxides (167) (Scheme 2.59) (324). 

The 2H -imidazole A-oxides (225) have significantly higher oxidation potentials than their AH -imidazole isomers (223) and (224) but oxidation potentials of 2H -imidazole A, A-dioxides (226) are similar to oxidation potentials of AH -imidazole A,A-oxides (219) (Fig. 2.18) (Table 2.7) (427). 

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... 

As is the case with the 1 //-pyrroles and the 1 //-pyrazoles, structures isomeric with the 1//-imidazoles (1) exist that are nonaromatic because of the presence of a tetrahedral carbon atom in the ring. These structures, the 2H-imidazoles (2) and 4//-imidazoles (3), have properties quite different from their 1H counterparts. They also differ from each other in that the polarities of the two conjugated C=N bonds reinforce one another in structures 3, but are in opposition in structures 2. 

A reaction related to the preparation of 11 is the cycllzation of a-bromo-ketones with ammonia and a second ketone to give imidazolines 14, which are oxidized by sulfur in high yields to 2H-imidazoles 15 (Scheme 6) ... 

Conversion of the S=C—NH moiety in the 2//-imidazolethiones 13 to X—C=N, where X is a single-bonded group, generates the 2H-imidazole ring system. This has been accomplished in a number of ways, generally in high yields. 

Most routes make use of noncyclic precursors, although there have been two reports involving direct oxidation of 2H-imidazoles. 

Quaternization of the 2H-imidazole ring results in the expected down-field shift of methyl signals (e.g., 102). ... 

Most 2H-imidazoles show a parent ion that can be quite prominent.The major fragmentation pathway involves loss of RCN (two possible ways when the C-4 and C-5 substituents are different) and often gives rise to the base peak. Thus the 4-phenyl compounds show a prominent Mt — 103 ion, and structures 51 a common peak at m/e 145 (Mt -RCN). " °... 

Diphenyl-2H-imidazoles 120 have been shown to form methosalts 121 in high yields (Scheme 29) ethyl iodide, however, gave only small amounts of ethosalts. In 4-amino compounds, methylation occurs at the ring N-3. ... 

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