Imidazoles dimethylimidazole

Involvement of AModo species in electrophilic C-iodinations needs to be considered since a number of imidazoles are known to form such compounds in basic medium. Charge-transfer complexes, too, are quite well known. They seem to be of the n -type through the unshared electron pair at N-3. Equilibrium constants for their formation are known to increase regularly in line with electron-donating powers of substituents (or vice versa). Some KCT values at 20°C (L M are imidazole (200), 1-methylimidazole (333), 1,2-dimethylimidazole (1165), 4-phenylimidazole (152), and 4,5-diphenylimidazole (141) (83BSB923). The charge-transfer complexes formed between iodine and imidazole-2-thiones appear to involve the sulfur atoms (88JA2586). 

The effects of the substituents near the donor site is to reduce the number of coordinated ligand molecules from six to four or less. Tetrakis complexes with substituted pyrazoles and imidazoles are prepared using a large excess of the ligands, and, in the cases of 1,2-dimethylimidazole and 3,5-dimethylpyrazole derivatives, anhydrous reactants. Most of die mono and bis adducts may be conveniently prepared under anhydrous conditions and with the nickel salt in excess. 

The acid-base properties of 4-nitroso-5-aminopyrazoles 50 have been studied. In particular, protonation sites have been determined where salts 51 are formed [66], The effects produced on II, 13C, and 15N chemical shifts by protonation and by hydrogen-bonding solvents on five azoles (imidazole, 4,5-dimethylimidazole, pyra-zole, 3,5-dimethyl-pyrazole, and 4,5-dihydro-3-methyl-2//-benz[g]indazole) have been determined experimentally. Phase effects on the 13C chemical shifts of the C-4 atom of pyrazole were discussed, based both on empirical models and on GIAO calculations of absolute shieldings in different complexes. The special case of the chemical shifts of pyrazoles in the solid state, where they form multiple N-H N hydrogen bonds, was also studied theoretically [88],... 

Whereas the radical anion formed from l-methyl-2(thiomethyl)imidazole has a 7r SOMO, 4-bromo- and 4-iodo-2-methylimidazole, 5-bromo- and 5-iodo-l,2-dimethylimi-dazole and 4,5-dibromo- and 4,5-di-iodo-l,2-dimethylimidazole form cr radical anions in irradiated methanol or MeTHF solutions at 77 K251. 

Recent Japanese patents158 relate to the preparation of 2,4,5-trimethylimidazole (and other U-substituted imidazoles) when 3-aminobut-l-yne is refluxed for 5 hours with acetamide. 3-Butynyl-thiourea (39) and 3-butynylurea are converted by concentrated sulfuric acid into 4,5-dimethylimidazole-2-thione (40) and 4,5-dimethyl-2-imidazolone, respectively. The latter compound is also... 

The reaction mechanism is similar to the one employed by Raubenheimer el al. for their chromium(O) thiazol-2-ylidene complex [48], In the case of the ruthenium imidazol-2-ylidene complexes, 4,5-dimethylimidazole stabilised the carbene complex compared with unsubstituted imidazole. Likewise, the carbonyl ligand in trans position was necessary to isolate and crystallise the complex. This can be expected, when an excellent o-donor (NHC) is trans to an excellent tr-acceptor (CO). 

Reaction of l-benzyM,5-dimethylimidazole 3-oxide 362 with thioketene 363 in CDCI3 at room temperature for 2h gave a mixture of deoxygenated imidazole 364 as well as imidazole-2(3//)-thione 365 in 84% and 15% yields, respectively. Thiiranone 366 and ketene 367 were also obtained in 70% and 14% yield, respectively (Equation 54) <1998HCA1585>. 

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