Sodium imidazolide

From an electron-deficient sodium imidazolide PhCH20P (NMe2)3 PF, DMF, 24 h, heat, 40% yield. ... 

In the fully and partially unsaturated oxygenated series, the syntheses of 2,5-dimethoxycarbonyl-3,6-diphenyl-l,4-dioxin 231 and 2,6-dimethoxycarbonyl-3,5-diphenyl-l,4-dioxin 232 were recently reported from methyl phenylchloro-pyruvate with potassium phthalimide and sodium imidazolide <2000CHE911>. 

This ring is formed by reaction of neighbouring hydroxy and lactam thiocar-bonyl groups with carbonyldi-imidazole and sodium imidazolide (Naim) at or below room temperature. The product is a cyclic thiocarbonate which acylates amines under mild conditions. 

High yields are obtained by preparing the sodium imidazolide from imidazole and sodium hydroxide, which subsequently reacts with the haloalkane or a dialkyl sulfate in dichloromethane, acetonitrile or methanol [116]. Because of the ambident character of the imidazolyl anion, 4- or 5-substituted imidazoles yield mixtures of 1,4- and 1,5-disubstituted imidazoles, e.g. ... 

The reaction of sodium imidazolide with fluoroalkyl iodides and bromides afforded the corresponding 4-fluoroaIkylimidazoles (Scheme 29) [42]. A decrease in conversion was observed by conducting the reaction in the dark (in comparison to visible light) as well as in the presence of 20 mol% of p-DNB or hydroquinone additive. An Srn mechanism was suggested for these conversions due to the known difficulty in displacing the halides of perfluoroalkyl halides by Sn or Sn processes. 

Of great preparative potential with respect to the activation of carboxylic acids to imidazolides is A -oxalyldiimidazole, which reacts with carboxylic acids or their sodium or lithium salts under release of CO and CO2 to give imidazolides in excellent yield.[23]... 

The second step, nucleophilic attack of an alcohol or phenol on the activated carboxylic acid RCOIm (carboxylic acid imidazolide), is usually slow (several hours), but it can be accelerated by heating[7] or by adding a base[8] [9] such as NaH, NaNH2, imidazole sodium (ImNa), NaOR, triethylamine, diazabicyclononene (DBN), diazabicycloimdecene (DBU), or /7-dimethylaminopyridine to the reaction mixture (see Tables 3—1 and 3—2). This causes the alcohol to become more nucleophilic. Sodium alcoholate applied in catalytic amounts accelerates the ester synthesis to such an extent that even at room temperature esterification is complete after a short time, usually within a few minutes.[7H9] This catalysis is a result of the fact that alcoholate reacts with the imidazolide very rapidly, forming the ester and imidazole sodium. 

The broad use of A -carbonyldiimidazole (CDI) for the synthesis of amide and peptide linkages became a routine method only in the early sixties. JV-Protected amino acids were treated at room temperature with an equimolar amount of CDI to give imidazolides. Anhydrous tetrahydrofuran, dimethoxyethane, dichloromethane, pyridine, dimethylfor-mamide, and diethyl phosphite were utilized as solvents. In the second step the esters of amino acids, their hydrochlorides, or sodium salts were added to yield the peptide after several minutes or hours of reaction time. 

Imidazolides of aromatic sulfonic acids react much more slowly in alcoholysis reactions than the carboxylic acid imidazolides. Although the reaction with phenols is quantitative when a melt is heated to 100 °C for several hours, with alcohols under these conditions only very slight alcoholysis is observed. In the presence of 0.05 equivalents (catalytic amount) of sodium ethoxide, imidazole sodium, of NaNH2, however, imidazolides of sulfonic acids react with alcohols almost quantitatively and exothermically at room temperature in a very short time to form sulfonic acid esters (sulfonates). (If the ratio of sulfonic acid imidazolide to alcoholate is 1 2, ethers are formed see Chapter 17). The mechanism of catalysis by base corresponds to that operative in the synthesis of carboxylic esters by the imidazolide method. Because of the more pronounced nucleophilic character of alkoxide ions, sulfonates can also be prepared in good yield by alcoholysis of their imidazolides in the presence of hydroxide ions i.e., with alcoholic sodium hydroxide. 45 Examples of syntheses of sulfonates are presented below. 

Nitroalkanes can be acylated by imidazolides via their sodium, potassium, lithium, or ammonium salts in refluxing THF or in DMSO. Acylation in this case takes place exclusively at the a-carbon of the nitro compound. 

Addition of / -toluenesulfonic imidazolide in benzene to a suspension in benzene of sodium cinnamoxide in a 1 2 molar ratio affords the dicinnamyl ether in 71% yield. Apparently, a highly reactive, so far not isolated sulfonate of cinnamyl alcohol is formed first (a), which then reacts further with a second mole of alkoxide to form the ether according to (b) ... 

These reactions correspond to the transformation of sodium benzylalcoholate with benzenesulfonic acid imidazolide, leading to A/-benzylimidazole[10] (see also references [11] and [12]) ... 

Phenols can be converted with trifluoromethylsulfonic imidazolide in the presence of sodium hydride into the corresponding trifluoromethylsulfonates, which react with potassium amide/ammonia to give aromatic amines. 15]... 

Explanation 70 is a big surprise. On heating for weeks at 90°C with a large excess of sodium salt of a hydroxy compound in A.iV -dimethyl-imidazolid-2-one, all fluorine atoms are replaced by the residues of the hydroxy compounds such as m-cresol, 2-naphthol, or 2-hydroxytetralin. Compound L is octakis(alkoxy)- or octakis(aryloxy)naphthalene [98]. 

A mild and convenient method has been attained by using the imidazolide (8 equation 6) or triazolide (9 equation 7) of carboxylic acids as a key intermediate. Treatment of an imidazolide of carboxylic acid with 1.2 equiv. of benzeneselenol and 0.02 equiv. of sodium phenoxide provided the selenol ester in a quantitative yield. In the case of the triazolide of carboxylic acids, the reaction proceeded in the absence of base.2 ... 

Acyl chlorides may be replaced with imidazolides, which react with sodium azide to give acyl azides. In the reaction shown in equation (34), 2-trimethylsilylethanol is used for trapping the isocyanate. The resulting 2-trimethylsilylethyl ester is easily cleaved with tetra-n-butylammonium fluoride. 

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