Hydrolysis nitrobenzyl ester

The related reaction for o-nitrobenzyl esters results in hydrolysis of the ester, and this has been developed for use in the protection of alcohols, carboxylic acids and amines. For example, the C-1 hydroxyl group in carbohydrates con be protected as its o-nitrobenzyl ester, and the ester group removed under the very mild conditions of irradiation in neutral solution (5.51). Similarly, the carboxylic acid... 

Rarely does an acid generator possess all of these attributes in the required measure. For instance, the diazonium salts produce Lewis acids (e.g., BF3) and are not thermally stable however, on the other hand, the sulfonium and iodonium salts are very thermally stable, but because they are ionic, can be particularly difficult to incorporate into resist formulations. The triazines and bromobisphenol-A produce halogen acids that are volatile, while the nitrobenzyl esters tend to undergo unwanted facile hydrolysis. ... 

Hydrolysis of cephalosporin / -nitrobenzyl esters by microbial enzymes has been described. A convenient high-yield method for preparing benzhydryl esters of penicillins and cephalosporins has been described. Diphenyl-diazomethane is generated in situ in the presence of the antibiotic by oxidation with peroxyacetic acid of benzophenone hydrazone. Diazomethane has been found to add to 3-methyl-A -cephem sulphides, sulphoxides, and sulphones preferentially from the j3-side to give the respective pyrazolino-cephams (194 b). ... 

If only the O-H, as opposed to the carbonyl, of a carboxyl group has to be masked, it can be readily accomplished by esterification. Alkaline hydrolysis is the usual way for regenerating the acid. t-Butyl esters, which are readily cleaved by acid, can be used if alkaline conditions must be avoided. 2,2,2-Trichloroethyl esters, which can be reductively cleaved with zinc, are another possibility.267 Some esters can be cleaved by treatment with anhydrous TBAF. These reactions proceed best for esters of relatively acidic alcohols, such as 4-nitrobenzyl, 2,2,2-trichloroethyl, and cyanoethyl.268... 

A few papers on phosphonate chemistry have appeared.235-237 The synthesis of die novel nucleoside bicyclic trisanhydrides (256 A = adenosin-r -yl) has been reported.235 A kinetic sriidy of the alkaline hydrolysis of 4-substiriited phenyl ethyl benzyl phosphonates (257) supports an associative A-E mechanism for the hydrolysis.236 The direct preparation of the esters of /Miitrobenzylphosphonic acid from /r-nitrobenzyl halides has been reported.237... 

The methods are especially suitable for optimizing industrial enzymes. For example, we have recently directed the evolution of an enzyme to catalyze a nonnatural reaction, p-nitrobenzyl (pNB) ester hydrolysis in the presence of... 

Enzymatic hydrolysis of the methyl ester of 350 with pig liver esterase on Eupergit gave the unstable 350 which was then esterified at pH 8 in a one-pot process with 4-nitrobenzyl bromide in the presence of a phase-transfer catalyst and dichloromethane to give 353 <2003TL973>. 

TrifiuoroacetyUuion. Trifluoroacetic anhydride acylates primary and secondary alcohols with great ease, but the esters are so extremely sensitive to hydrolysis that it is sometimes necessary to avoid contact with water in the workup. Thus Tatlow and co-workers refluxed briefly a mixture of p-nitrobenzyl alcohoi, trifluoroacetic anhydride, and sodium trifluoroacetate and distilled the mixture with four portions of carbon tetrachioride at reduced pressure to remove excess anhydride and trifluoroacetic acid. The ester was then extracted from the sodium trifluoroacetate... 

Smutny. The t-butyl ester was used in order to achieve hydrolysis of (30), which required reaction with trifluoroacetic acid at 0 °C for 4—5 h. Treatment of (30) with warm trifluoroacetic acid for 10 min yielded (31). The reaction of (29) with ethyl a-chloroacetate gave (32). A-Phenyl phenylpropynthioamide (33) reacts in a similar manner with active bromomethylene derivatives, such as bromo-acetonitrile, bromonitromethane, and /j-nitrobenzyl bromide, in the presence of triethylamine to give the thiophen (33a). Instead of enamine thioesters such as (29), 2-aminovinyl thioketones (34) react with a-bromo-ketones in the presence of triethylamine to give 2-acyl-thiophens (35). By the ion-pair extraction method, tetrabutylammonium salts of acetylacetone were allowed to react with carbon disulphide to give (36), which upon reaction with chloroacetone gave a 45% yield of the thiol (37), in addition to a thieno[2,3-A]thiophen derivative. ... 

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