Ethyl imidazole catalyst

Fortunately, as the reaction is transferred from a purely organic solvent system to mixed organic-aqueous media, which are employed in most RP-HPLC separations, the apparent multiplicity of maxima in the time profile of the intensity dependence seems to be suppressed or to collapse to a reasonably simple biexponential-like dependence. As shown in Figure 11, simply changing the solvent from ethyl acetate to 95% aqueous acetonitrile and the catalyst from triethylamlne to imidazole produces a single maximum profile, one that is more easily modeled mathematically, as defined in Equation 4 ... 

Imidazole has been condensed with ethyl acrylate by using two basic clays (Li+ and Cs+ montmorillonites) as catalysts in a microwave oven [70]. The role of alkali promoters (Li+ and Cs+) was studied and it was found that the greater the basicity and the irradiation time and power, the higher were the conversions. The yield of N-sub-stituted imidazole is maximum for 0.1 g Cs+ montmorillonite at 850 W after irradiation for 5 min (Scheme 8.48). 

The microwave activation of Michael additions in the preparation of N-substituted imidazoles afforded excellent yields in very short reaction times under mild reaction conditions, Scheme 10.9. Basic clays (Li+, Cs+) exchanged montmorillonites were found to be very active and selective catalysts for the Michael addition of imidazole and ethyl acrylate [54]. 

This preparation is carried out in an aprotic solvent (e.g. benzene, chloroform) with no special provision other than working in a well-ventilated fume hood to avoid ill-smelling sulfur compounds. Various ligands have proved successful phosphines, pyridines, imidazoles, tetra-m ethyl thiourea, etc. When the same reaction is carried out in the absence of the Lewis base L, a dimer 6 is obtained, which is a useful catalyst in its own right and sometimes a much more active one see Section VILA. The chemical equation for that reaction is,... 

Cyclohexane is a saturated hydrocarbon in which no regioselectivity problems of C-H insertion can occur. The reaction of cyclohexane with ethyl diazoacetate was investigated in a thorough study by Perez et al.14 The /V-heterocyclic carbene ligand IPr (IPr= l,3-bis(diisopropylphenyl)imidazol-2-yliden) was used, all three compounds IPrMCl (M = Cu, Ag, Au) were inactive as catalysts in cyclohexane (Table 12.2, entry 1). Addition of the sodium BARF salt (NaB[3,5-(CF3)2C6H3]4) gave ethyl cyclohexyl acetate as the C-H insertion product of the carbene (Scheme 12.4). 

Epoxynovolak resin and BPA/DC-BMI prepolymer, tert.butyl peroxide and Zn acetate [106, 107] or 2-phenylimidazole and other catalysts [108] were filled with wollastonite. Carbon-fiber reinforced composites were obtained using a binder, which consisted of BPA/DC, BMI, an epoxynovolak, 2-ethyl-4-methylimidazole and an organic solvent [109]. A BPA/DC-BMI prepolymer in methylethylketone was mixed with middle-molecular-weight epoxide resin (Epikote 1001), 2-ethyl-4-methyl-imidazole, Zn acetate and triethylenediamine thermal shock resistant GRP was thus obtained [110]. 

The 2-ethyl-4-methyl-imidazole (EMI) is not a tertiary amine however, it is used in the same manner as a single catalyst or as an accelerator. EMI is a substituted imidazole that is a liquid at room temperature (4000 to 8000 cP at 25°C) with a high boiling point. 

In the studies of the synthesis of the ansamycin antibiotic rifamycin S (13S), Corey and Clark [76] found numerous attempts to effect the lactam closure of the linear precursor 132 to 134 uniformly unsuccessful under a variety of experimental conditions, e.g. via activated ester with imidazole and mixed benzoic anhydride. The crux of the problem was associated with the quinone system which so deactivates the amino group to prevent its attachment to mildly activated carboxylic derivatives. Cyclization was achieved after conversion of the quinone system to the hydroquinone system. Thus, as shown in Scheme 45, treatment of 132 with 10 equiv of isobutyl chloroformate and 1 eqtuv of triethylamine at 23 °C produced the corresponding mixed carbonic anhydride in 95% yield. The quinone C=C bond was reduced by hydrogenation with Lindlar catalyst at low temperature. A cold solution of the hydroquinone was added over 2 h to THF at 50 °C and stirred for an additional 12 h at the same temperature. Oxidation with aqueous potassium ferricyanide afforded the cyclic product 134 in 80% yield. Kishi and coworkers [73] gained a similar result by using mixed ethyl carbonic anhydride. 

When the 2-aldehyde of imidazole (209) is treated with ethanol some decarbonylation takes place by way of a nucleophilic attack of the alcohol on the carbonyl carbon (Scheme 111). The products isolated are imidazole and ethyl formate. One would normally expect that acetal formation would result under these conditions, but it appears that in the acid-catalyzed formation of acetals from (209) the yield of acetal depends on the amount of catalyst. When the ratio of imidazole is >1, then the diethyl acetal is produced in high yield. When this ratio falls to less than unity there is some decarbonylation, and in the absence of acid only decarbonylation occurs. Electron-withdrawing groups in the heterocyclic nucleus (or quaternization) assist this reaction which does not appear to occur with 4- or 5-aldehyde functions (80AHC(27)241). 

Microwave irradiation of a mixture of an acid anhydride, an amine adsorbed on silica gel, and TaCl5/Si02 is a solvent-free method for the synthesis of A-alkyl and A-aryl-imides [47]. Ni(II) promotes the conversion of an acrylamide to ethyl acrylate via a Diels-Alder adduct with (2-pyridyl)anthracene [48], Aromatic carboxylic acids [49] and mandelic acid [50] are efficiently esterified with Fc2(S04)3 XH2O as catalyst. Co(II) perchlorate in MeOH catalyzes the methanolysis of acetyl imidazole and acetyl pyrazole [51]. Hiyama et al. used FeCb as a catalyst for the acylation of a silylated cyanohydrin. The resulting ester was then cyclized to 4-amino-2(5H)-furanones (Sch. 5) [52]. 

The decarbonylation of imidazole-2-aldehyde in ethanol involves nucleophilic attack by the alcohol on the carbonyl carbon (see Scheme 42) to give the imidazole and ethyl formate." It was found that in the acid-catalyzed formation of acetals of imidazole-2-al-dehydes the yield of acetal depended on the amount of catalyst. When the H imidazole ratio is >1, good yields of the diethylacetal are obtained, but when the ratio is < 1 decarbonylation occurs to some extent. When only ethanol is used (no acid) only decarbonylation takes place. Electron-withdrawing groups on imidazole assist the reaction, as does quaternization, and it does not occur with 4- and S-aldehydes." ... 

The ionic liquid l-ethyl-3-methylimidazole acetate ([emim][OAc]) was found to be a mild and effective catalyst for the efficient, one-pot, three-component synthesis of 2-aryl-4,5-diphenyl imidazoles at room temperature under ultrasonic irradiation (Fig. 12.42) [28],... 

Some difunctional compounds, for example. A -(ethoxycarbonyl)thiocar-boxamides, may behave as monofunctional reagents in a reaction with a diamine. In this example, an ethoxycarbonyl group is eliminated as ethyl carbamate and the thioamide completes the imidazole ring [2899]. Diamines usually react with 3-oxo esters to give a fused dia pine (p. 423), but when the reactants are heated without a solvent or catalysts at or above 100 °C, a benzimidazole is obtained in high yield [2371]. 

The second type of composition is exemplified by a wide variety of acrylate- or methacrylate-ester derivatives of conventional ink vehicles combined with a photoinitiator 1. The reaction product of tung oil fatty acids, glycidyl methacrylate, -benzoquinone, and 2-methyl-imidazole mixed with tung oil and treated with tolylene diisocyanate, combined with benzoin methyl ether (26) 2. Glycerol-linseed oil-isophthalic acid alkyd reacted with isocyanate-containing prepolymer (formed by reaction of tolylene diisocyanate, -henzoquinone, 2-hydroxypropyl acrylate in ethyl acetate solution) using dibutyltin diacetate catalyst, combined with tung oil, synthetic varnish, and benzoin methyl ether (27) 3. Epoxidized... 

Polystyrene-supported proline 348 has been used as co-catalyst (10 mol.%) with imidazole (10 mol.%) in the MBH reaction between methyl or ethyl vinyl ketone and aromatic aldehydes (Scheme 2.188). Recycling studies showed that the proline resin can be used up to five cycles in high isolated yields. This study was the first example of supported proline as a heterogeneous co-catalyst in the MBH reaction and broadened the scope of this catalytie material. ... 

The epoxidation of olefins in the presence of ethyl 2-oxocyclopentanecarboxylate as co-substrate by 1/f-imidazole and air using FeCl3 6H20 in MeCN as catalyst was achieved with fair to excellent chemoselectivities. The epoxidation was caused by an active iron species generated by O2, which was activated by the co-substrate. The process involved 4e , instead of 2e , reduction of the O2 molecule in the commonly used peroxides. Aromatic olefins were also oxidized in high yields with excellent chemoselectivity.i2 ... 

Botta and coworkers have used the enyne metathesis in the synthesis of the enantiopure antifungal agent (5 )-bifonazole 130 [47]. In this work, the diene for the Diels-Alder reaction had to be synthesized from an alkyne. Reaction of alkyne (R)-131 with ethyl vinyl ether, in the presence of catalyst 2-Ru, thus afforded the desired diene 132 (Scheme 17.25) in an excellent yield of 88%. Next, the diene 132 was reacted with methyl vinyl ketone in a Diels-Alder reaction to afford compound 133. Exposure of compound 133 to acid and then DDQ yielded the aromatic product 134, where a newly formed benzene ring had been assembled. Further manipulations, including the formation of the required imidazole ring, allowed for the enantioselective synthesis of (S)-bifonazole 130. 

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