2- benzoate esters protect alcohols

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. ... 

Dibromo)fluorenylmethyl carbamates, to protect amines, 319 o-(Dibromomethyl)benzoate esters, to protect alcohols, 112... 

Heating the epoxides in THF with either (n-Bu NLi or LDA led to the expected diol 56 in 45% yield (two steps). All attempts to oxidize selectively the allylic alcohol met with failure selective protection of the secondary hydroxyl group in 56 as a benzoate ester and oxidation using PCC afforded the desired enone 51 in 76% yield after crystallization. 

Protection of an alcohol function by esterification sometimes offers advantages over acetal protecting groups such as the tetrahydropyranyl ethers. Generally, acetals are stable in base and labile in acid, while esters are more stable in acid than acetals and are readily hydrolyzed in base. Esters are notably useful in reactions such as oxidations, but are not satisfactory in organometallic reactions. Acetates and benzoates are the most common ester protecting groups 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 amine. The use of reactive amides such as N-acylimidazoles (imidazolides) allows the reaction to be carried out in the absence of added bases ... 

As before, the hydroxy group of this epoxy alcohol was subjected to a Mitsonobu esterification and subsequent cleavage of the resulting benzoate ester 14 to afford epoxy alcohol 15, with the desired relative stereochemistry, in 87 % yield over two steps. The free hydroxy group was protected, as previously, with a benzyl group in 96 % yield. 

Full details have appeared of the a-oxo-lithiation of 2,6-disubstituted benzoate esters (6) having sterically protected carbonyl groups (c/. 3,133). Reaction of the lithio derivatives, formed from (6) by reaction with excess base or regenerated from the stannane (7) by treatment with stoicheiometric methyl-lithium, with alkyl halides or carbonyl compounds followed by ester cleavage leads to alcohols and diols, respectively (Scheme 9). 

The formation of acetate or benzoate esters produces crystalline carbohydrate derivatives that were much sought by the organic chemists of the late nineteenth century. Because of their facile formation and easy removal under basic conditions (see discussion later), acetate and benzoate esters can be used to protect carbohydrate alcohol groups from undergoing reaction in synthetic procedures. Furthermore, the acetate derivatives are often volatile, especially the alditol acetates, permitting their use in gas chromatographic analyses of carbohydrates. 

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