Imidazole N-methyl

Computations performed on an N-methylated imidazole showed that the presence of the methyl group increases the proton affinity of the other nitrogen. In contrast, a peptide substituent at a carbon adjacent to the nitrogen decreases its proton affinity. This can be explained by the conjugation stabilization of the peptide-substituted neutral form, which is absent in the protonated form. This result seems to indicate that heteroatomic rings linked by... 

Derivatives of bzacen have been studied to a minor extent [Fe(bzacen) (N-methyl-imidazole)2]C104 [176] and [Fe(bzacen)(Him)(CN)] [185] are purely low spin, whereas [Fe(bzacen)(Him)2]BPh4 shows gradual spin crossover [185]. 

Histamine is rapidly degraded by oxidative de-samination by the diaminooxidase histaminase, acetylation of the NH2-group, methylation of the ring and oxidation of the methylhistamines by the mono-aminoxidase. The main metabolites are the N-methyl-imidazole acetic acid and the imidazole acetic acid. Histamine interacts with at least four different specific receptors Hi to H4 (see Table 1). 

Scheme 11 Synthesis of ionic liquids via solvent-free alkylation of N-methyl imidazole [63]...

An interesting photochemical approach to 4,5-disubstituted N-alkylimidazoles consists of the photolysis of 2,3-dihydro-5,6-disubstituted-pyrazines that can be easily prepared from 1,2-diketones and 1,2-diamino-alkanes. For example, the preparative-scale photolysis, in absolute EtOH with high-pressure Hg lamp (Pyrex filter), of 5,6-dimethyl- or 5,6-diphenyl-2,3-dihydropyrazines 54, yields the corresponding N-methyl-imidazoles 57 in high yields (Scheme 12.16). The reaction mechanism involves the formation of an enediimine intermediate 55, followed by cyclization and re-aromatization [41]. 

Dichloroacetamido)-l-methyl-5-nitroimidazole undergoes a 1,3-dipolar cycloaddition reaction with diazomethane to give (dichloroacetimino)tetrahydroimidazo[4,5-c]pyrazoles in about 10% each (Scheme 5). The failure to observe cycloaddition with l,2-dimethyl-5-nitroimidazole underlines the role of the N- methylated imidazole intermediate (184), a typical non-aromatic a, j6-unsaturated nitro compound acting as a dipolarophile (80TL4757). 

H202, cat chiral Mn(ni)-salen, cat N-methyl-imidazole (enantioselective)... 

Figure 3.39 Differential pulse voltammograms of Co2FTF4 adsorbed on a graphite electrode in aqueous solutions pH =8 in the absence (solid curve a) and in the presence of 1 mM N-methyl imidazole (NMI) (dashed curve b) and 10mM NMI (dotted curve c).

Catalyst precursors modified with other types of hgands, such as bis(N-methyl-imidazole) 27 [56], N-heterocyclic carbene chelates 28 [57], and cahx[6]arene-derived... 

A, A, and A represented the absorbancies at initial time, at completion of the reaction, and at the time of measurement, respectively, k was considered to be a pseudo first-order rate constant defined by the expression -dc/dt = k C(C/C ), where C/Cq represents the relative reactivity of the ester groups on a pol3nner chain as a function of extent of reaction. A reasonably good fit to this was obtained for reactions conducted in the absence of catalysts as well as in those catalyzed by N-methyl-imidazole and poly-(N-vinylimidazole). 

Trans complexes with the general formulas [PtCl2(L)2] (L = pyridine, N-methyl-imidazole and thiazole) or [PtCl2(L)(L )] (L = quinoline and V = RR SO where R = methyl and R = methyl, phenyl benzyl or L = quinoline and V = NH3) (Fig. 14.16) showed comparable activity to cisplatin and greater activity than trans-platin in cisplatin-sensitive and -resistant cell lines [51-54]. 

The dark colour of polyether polyols obtained in the presence of imidazoles as catalysts (Gardner colour >18) can be improved substantially by the treatment with hydrogen peroxide (50% concentration) of around 0.1-0.3% against the polyol. The dark brown colour is the colour of the catalyst and it is not a consequence of polyether destruction. A better final colour is obtained using N-substituted imidazoles (such as N-methyl imidazole) [36]. 

Initial porphyrin CH2CI2 CH2Q2 -1- 1 M N-methyl-imidazole Pyridine ... 

Michael/Henry/dehydration/aromatisation reaction of 2-(2-oxoethyl) benzal-dehydes and nitroalkenes mediated by pyrrolidine to obtain polysubstituted naphthalene derivatives. DBU catalysed the conjugate additions of alcohols to ot,p-unsaturated nitriles, esters and ketones. Perhaps more important are the aza-Michael addition reactions of amines to a,p-unsaturated ketones, nitriles and esters. Recently, Costa, Vilarrasa and coworkers described the addition of lactams, imides, 2-pyridone, pyrimidine-2,4-diones and inosines to methyl propiolate and other similar compounds, DABCO and DMAP being the best catalysts. As mentioned before, tertiary amines give zwitterionic species with activated allynes. It was as early as 1932 when Diels and Alder used the reaction of pyridine with dimethyl acetylenedicarbojylate (DMAD) for the synthesis of heterocycles. The interception of the corresponding intermediate with Al-tosylimines and activated olefins provided access to l-azadienes ° and highly substituted butadienes (Scheme 2.6). When the quenching species of the zwitterionic intermediate is a 1,2-diketone, dibenzoyl maleates or cyclopentenedione derivatives could be obtained (Scheme 2.6). The interception of the zwitterionic species of N-methyl imidazole (NMI) and DMAD with ketenes to obtain unsaturated esters has also been shown. ... 

The substitution of sodium acetate or N-methyl-imldazole for pyridine in the preparation of alditol acetate derivatives for the capillary g.c. analysis of neutral and amino-sugars using selected ion monitoring m.s. detection has been examined. While N-methyl-imidazole effected full acetylation of alditols in the presence of borates and water, it led to a higher detector background than the more tedious use of sodium acetate. Muramic acid produced two alditol acetate derivatives, the lactams (1) and (2), in a reproduceable fashion only in the sodium acetate-catalyzed procedure... 

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