Benzoate esters stable

The benzoate ester is one of the more common esters used to protect alcohols. Benzoates are less readily hydrolyzed than acetates, and the tendency for benzoate migration to adjacent hydroxyls, in contrast to acetates, is not nearly as strong. Benzoates can be forced to migrate to a thermodynamically more stable position. ... 

Bundgaard, H., E. Jensen, and E. Falch. 1991. V feter-soluble, solution-stable, and bfoMabttetituted (aminomethyl)benzoate ester prodrugs of acycIcRiiarm. Res8 1087-1093. 

Benzoate esters are reduced under aprotic conditions initially, as mentioned earlier, to the corresponding anion radical. The anion radicals are not stable for long periods of time, however, and generally cleave, giving benzoate and the alkyl radical as in Eq. (15) [56-58]. 

Alkynyl carboxylate esters, 75, are obtained in the reaction of lithium acetylides with bis(acyloxy)iodobenzene, 73 [Eq. (32)] [59], These reactions are likely to proceed through the intermediacy of the respective alkynyliodonium carboxylates (74), although no such salts have been isolated to date as they spontaneously decompose, via loss of iodobenzene, to the alkynyl carboxylates, 75. Only benzoate esters (75 R = CgHj) are sufficiently stable to isolate and store pure for longer periods. Simple alkylcarboxylates such as acetates are not stable although the hindered pivaloate ester (65 R = t-Bu, R = t-Bu) has been isolated in low yield [59]. Among the reasons for the instability of these esters is their sensitivity to moisture they both readily add water and undergo subsequent hydrolyses [60]. Because of the sensitivity to moisture, the isolated yield [41] of bisalkynyl benzoates, 76, from the bisalkynyliodonium triflates, 35, is only 6-15% [Eq. (33)]. 

Highly regioselective oxidation of the carbon next to a heteroatom such as oxygen and nitrogen has been accomplished on illuminated semiconductor particles. One example is the formation of benzoate esters from the photooxidation of benzyl ethers on Ti02 [Eq. (18)] [137]. The selectivity is the result of a stable benzyl radical cation. 

Chloroformate (6) reacts with alcohols in pyridine at room temperature to afford carbonates (7). The 2-phenylsulfonylethoxycarbonyl (PSEC) group is stable to the conditions required to cleave tetrahydropyranyl (THP) ethers, 2-trimethylsilylethoxy carbonates (TEOC), and levulinate and benzoate esters. The alcohol can be r enerated when desired by treatment with triethylamine in p3nidlne (eq 4). 

The selectivity here relies on the fact that the j3-benzoate is the thermodynamically more stable ester. A mixture of esters is formed upon hydrolysis of the ortho ester and is then equilibrated with DBU. Carbohydrates are selectively protected with this methodology. " ... 

The search for catalysts which are able to reverse the ratio of cyclopropane diastereomers in favor of the thermodynamically less stable isomer has met with only moderate success to date. Rh(II) pivalate and some ring-substituted Rh(II) benzoates induce cw-selectivity in the production of permethric acid esters 77,98 99 contrary to rhodium(II) acetate, which gives a 1 1 mixture 74,77,98), and some copper catalysts 98) (Scheme 10). 

Protection of an alcohol function by esterification sometimes offers advantages over use of acetal or ether groups. Generally, ester groups are stable under acidic conditions. Esters are especially useful in protection during oxidations. Acetates and benzoates are the most commonly used ester derivatives. They can be conveniently prepared by reaction of unhindered alcohols with acetic anhydride or benzoyl chloride, respectively, in the presence of pyridine or other tertiary amines. 4-Dimethylaminopyridine (DMAP) is often used as a catalyst. The use of A-acylimidazolides (see Section 3.4.1) allows the... 

Pentamethoxyphosphorane, PfOCHj),. Mol. wt. 186.15, b.p. 37°. The material can be prepared in about 55% yield by reaction of trimethyl phosphite with methyl benzenesulfenate (which is converted during the reaction into diphenyl disulfide). It is stable to 80°. It reacts with acids to form methyl esters (methyl benzoate, 90% yield). It converts phenols into methyl ethers (anisole, 90% 2,4-dimethylanisole, 77% thioanisole, 87%). ... 

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