Imidazole as reagent

Identification of compounds s. subentry derivatives Imidazole as reagent (s. a. N,N -Carbonyldiimidazole) 19, 232... 

Identification of compounds s. subentry derivatives Imidazole as reagent... 

Per-2-naphthoate derivatives of alditols from neutral and amino-sugars were best synthesized using (2-naphthoyl)-imidazole as reagent. They separated well by h.p.Lc. on silica and were detected fluorimetrically at the sub-picomole level. ... 

Electrophilic bromination (and nitration) of pyrido[l, 2-a]benzimidazole (analogous to 132) cannot take place in the imidazole moiety. Initial substitution, using NBS as reagent, was shown to occur at the 8-position, and subsequently at C-4 and C-6 (90JOU1166). 

Procedure Weigh accurately about 0.17 g of amoxycillin trihydrate and dissolve in sufficient DW to produce 500 ml. Now, transfer 10 ml of this solution into a 100 ml volumetric flask, add 10 ml of buffer solution pH 9.0 followed by 1 ml of acetic anhydride-dioxan solution, allow to stand for 5 minutes, and add sufficient water to produce 100 ml. Pipette 2 ml of the resulting solution into each of the two stoppered tubes. To tube 1 add 10 ml of imidazole-mercury reagent, mix, stopper the tube and immerse it in a water-bath previously maintained at 60 °C for exactly 25 minutes, with occasional swirling. Remove the tube from the water-bath and cool rapidly to 20 °C (Solution-1). To tube 2 add 10 ml of DW and mix thoroughly (Solution-2). Immediately, measure the extinctions of Solutions 1 and 2 at the maximum at about 325 nm, as detailed above, employing as the blank a mixture of 2 ml of DW and 10 ml of imidazole-mercury reagent for Solution-1 and simply DW for Solution-2. 

Imidazole-containing compounds have been utilized as reagents for various synthetic transformations. A convenient access to substituted allyl enol carbonates was established through the reaction of ketone enolates with the complex of allyl l//-imidazole-l-carboxylates 74 and boron trifluoride etherate <07JOC9372>. Relatively mild and highly efficient Cul-catalyzed /V-arylation procedures for imidazoles with aryl and heteroaryl bromides or chlorides have been developed in the presence of ligands 75 and cesium carbonate <07JOC2737>. a, -Unsaturated 2-acyl imidazoles 76 are an alternative and practical class of dienophiles for the DNA-based catalytic asymmetric Diels-Alder reaction in... 

This classification is illustrated in Scheme 260. Formation of the 1,2- (or 2,3-) bond via the activation of an amide or urea group is a versatile method to synthesize imidazoles. Many reagents, such as PPh3-CCl4, PCI5, or acids, etc., have been used for the cyclization process. 

The initial research efforts focused on the preparation of the precursor, the omegar-r-butyldimethylsilyloxyalkyl halide, from the corresponding haloalcohol and /-butyldimethylsilyl chloride. The t-butyldimethylsilyl moiety was originally introduced as an alcohol protecting group by Corey. In this procedure, 1.2 equivalents of t-butyldimethylsilyl chloride and 2.5 equivalents of imidazole, as the acid acceptor, were utilized. The solvent employed was N,N-dimethylformamide. These reaction conditions afforded the desired product in excellent yield. However, the cost of the excess reagents, their subsequent removal, the utilization of an expensive, hydroscopic solvent, and an aqueous workup were not very practical from a commercial perspective. Since its inception in 1972, a variety of other procedures have been described for the preparation of t-butyldimethylsilyl ethers. These procedures typically require solvents that are expensive, difficult to recycle, or environmentally unfriendly. Furthermore, traces of some of these solvents, such as methylene chloride, in the precursor would be incompatible with lithium metal in the subsequent lithiation step. 

Chloroformates are useful analytical reagents for primary, secondary, and tertiary amines. The reaction of these reagents with amines can be performed easily, and the resultant carbamate derivatives are suitable for GC analysis. The carbamate derivatives obtained from primary and secondary amines are determined selectively and sensitively by GC-MS and -BCD. After dealkylation, tertiary amines are derivatized to carbamates in the same manner for primary and secondary amines. The carbamate derivatives obtained with pentafluorobenzyl chloro-formate are determined with high sensitivity by GC-ECD. Chloroformates also react with phenols, thiols, imidazoles, as well as amines. 

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