Imidazole-substituted olefins

Collman et al. have recendy reported that threitol-strapped manganese(IH)-porphyrin complex 7 shows high enantioselectivity in the epoxidation of a wide range of olefins when the reaction is carried out in the presence of 1,5-dicyclohexylimidazole (Scheme 6B. 12) [22], The substituted imidazole in this reaction appears to play the same role as the imidazole in Inoue s reaction. Detailed understanding of the mechanism of asymmetric induction by 7 needs further investigation, the major pathway should accommodate the steric interaction between the olefinic substituent and the inner oxygen atom of the threitol strap (Figure 6B.6). Thus, the pathway a is likely to be the major pathway,... 

Ketz et al. synthesised a keto functionalised imidazolium salt using the standard protocol by reacting the appropriate N-aryl substituted imidazole with the respective keto halide [95], Their intention was to use the corresponding nickel(II) carbene enolate complex in olefin polymerisation reactions similar to the phosphino enolates in the SHOP process [1 ]. It proved difficult to prepare the intended precatalyst with only one carbene enolate ligand attached to the nickel centre. Initially, the homoleptic complex with two carbene enolate ligands was formed. The authors pointed out that the high proportion of n-olefins is unusual. 

Besides the substitution of the olefinic hydrogens with other atoms or groups, other functional groups that bridge the two aryl moieties have been investigated, and they include different carbo- and heterocycles (for example, cyclopentenones, furanones, isoxazoles, imidazoles, pyridines, triazoles, and azetidinones) all of which possess varying levels of cytotoxicity. 

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. ... 

A key feature of many olefin polymerization catalysts based on square-planar nickel compounds is the presence of ligands, which provide considerable steric hindrance to access the sites of coordinative unsaturation above and below the square plane." " The complex /r 7/ .r-NiGl2 l,3-bis(2,6diisopropylphenyl)imidazol-2-ylidene 2 15 was synthesized from NiGl2(PPh3)2 by a ligand-substitution reaction." ... 

If has been shown lhal Irimethylsilylation of the sUanol groups of Ti-substituted mesoporous molecular sieves (Ti-MCM-41), a catalyst of olefin epoxidalion reactions in aqueous H2O2, improve the catal)ftic activity and the selectivity toward epoxide formation. A-(Trimethylsilyl)imidazole was the most effective in improving the hydrophobicity and catal)dic performance. ... 

Effluents from the manufacture of Pb(CH3)4 can be treated with an alkali metal borohydride, e.g., NaBH4 at pH 8 to 11 to substantially reduce the level of dissolved lead compounds, like [Pb(CH3)3][145, 146]. Zn can also be used [147]. Liquid NH3 and toluene are used to remove solid NH4Clfrom the apparatus for producing Pb(CH3)4 by the NH3- or amine-catalyzed reaction of CH3CI with a PbNa alloy [148]. Stabilization of Pb(CH3)4, and of antiknock fluids containing Pb(CH3)4, is accomplished by addition of compounds, like toluene [149], xylene [141, 150], styrenes [151], naphthalenes [149, 151, 152], anthracenes [152], substituted phenols [141, 152 to 155], olefinic hydrocarbons [152], alcohols [141, 152], amines [155], hydroquinones [156], ethers [141], saturated or unsaturated carboxylic acids [141, 152], esters of phosphoric acid [152], or of sulfuric acid [157], or of sulfonic acids [141], imidazoles [158], alkyl halides and alkyl thiocyanates [141], or tall oil [159] see also Organolead Compounds , Vol. 2, Section 1.1.1.2, to be published. 

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