4.5- Dimethylimidazole

With ethoxymethylenemalononitrile (136), C-addition appears to be the only mode of reaction with simple 5-aminoimidazole derivatives. Typically, reaction of 5-amino-1,2-dimethylimidazole (96 R = R2 = Me) with the reagent (136) in dioxane solution gave an 84% yield of the product (144 R = R2 = Me). In contrast, reaction of the same amine with diethyl ethoxymethylenemalonate (135) in dioxane solution gave exclusively an... 

A number of workers have made progress on this front. Asami and coworkers have anchored the stoichiometric base on the solid phase to realize a catalytic desymmetrization using lithiated diamine 135. Andersson has shown that slow addition of LDA results in an improvement in enantioselectivity when using his bicyclic base 136, while Ahlberg has illustrated that a stoichiometric base such as lithiated 1,2-dimethylimidazole results in an efficient catalytic system using diamine 137. Alexakis has published a smdy involving a number of chiral ethane-and propane-diamines in the catalytic deprotonation of cyclohexene oxide. Enan-tioselectivities observed are moderate, with diamine 138 providing the desired product in 59% ee and 80% yield. ... 

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). 

Triaryl phosphites are not effective as catalysts and alkyl isocyanates usually are not cyclized by phosphites at all, although benzyl isocyanates are reported to yield the corresponding uretidinediones with 1,2-dimethylimidazole as a catalyst (75S463). 

It has been reported that 2-methyl substitution on a 1-methylimidazole ring dramatically improves biodegradation from 0% after 31 days for 1-methylimidazole to 100% after 31 days in the case of 1,2-dimethylimidazole in the mixed microbial community of an activated sludge [47]. 

In general, mixed trimerization of isocyanates also gives mixtures (61JOC3334) however, it is possible to prepare isocyanurates of the type (157) from arenesulfonyl isocyanates in the presence of 1,2-dimethylimidazole as catalyst (76JOC3409). The mechanism is similar to that of the trimerization of isocyanates (Scheme 95). 

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. 

Azoles with bulky substituents near the donor site, such as 1,2-dimethylimidazole and 3,5-dimethylpyrazole, result in lower coordination numbers.36,37 When a ligand such as 3(5)-methylpyrazole is used, in which the methyl group is adjacent to the donor site in one tautomer and distant in the other tautomer, coordination takes place exclusively through the non-sterically-hindered form of the ligand, i.e. the 5-methylpyrazole. This has been proved by X-ray studies for this ligand38 and for indazole (4).39... 

The steric effects of the substituents, such as in 3,5-dialkylpyrazoles, may induce the coordination of small ligands or counterions that usually do not coordinate to transition metal ions. This behaviour is believed to be responsible for the unusual decomposition of transition metal tetra-fluoroborates in the presence of such ligands.43 Otherwise, the coordination number changes, resulting in, for example, square-planar Ni11 (low-spin) complexes, even with rather weak ligands such as 1,2-dimethylimidazole.44... 

Scheme 3. Asymmetric catalytic aminoalkylation as key step in the diastereo- and enantioselective synthesis of (2R,3S)-3-phenylisoserine hydrochloride (10) [20]. TBS = tert-butyldimethylsilyl, L = 1,2-dimethylimidazole, CAN = cerium ammonium nitrate.

Sulfonyl chloride Dansyl chloride, 1,2 -dimethylimidazole-4-chloride, pyridine-3-sulfonyl chloride 4-(l-H-pyrazol-l-yl)benzenesul-fonyl chloride [62] 10-Ethyl-acridine-2-sulfonyl chloride T631 Phenolic OH LC-ESP/MS/ MS LC-APCP/ MS/MS... 

Reactions with aldehydes and ketones in the 1,2-dimethylimidazole series. Side-chain lithiation of a 2-chloro-methylthiazole 574 leads to epoxides 575 (Scheme 122) <2003T1381>. Exposure of triazole 576 to LDA and then benzonitrile generates the bicyclic 577 <2003EJM959>. 

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