4-Methoxybenzyl esters cleavage

Dimethoxybenzyl esters prepared from the acid chloride and the benzyl alcohol are readily cleaved oxidatively by DDQ (CH2CI2, H2O, rt, 18 h, 90-95% yield). A 4-methoxybenzyl ester was found not to be cleaved by DDQ. The authors have also explored the oxidative cleavage (ceric ammonium nitrate, CH3CN, H2O, 0°, 4 h, 65-97% yield) of a variety of 4-hydroxy- and 4-amino-substituted phenolic esters. ... 

The acid lability of 4-methoxybenzyl (Mob) esters is comparable with that of tert-butyl or 2,4,6-trimethylbenzyl esters. Cleavage is accomplished by TEA at 0°C, formic acid at room temperature, or by HCl/MeN02 (30 The Mob esters are compatible with highly... 

The 4-methoxybenzyl esters are prepared by transesterification of N-protected amino acid nitrophenyl esters with 4-methoxybenzyl alcohol in the presence of several equivalents of imidazole, followed by subsequent acidolytic cleavage of the N-protecting group.Alternatively, reaction of N-protected amino acids silver(I) salts with 4-methoxybenzyl halides (TEA/CHCI3, rt, 24 h, 60% yield) or treatment of N-protected amino acids with 4-meth-... 

Benzylic oxidation of alkoxybenzyl ethers is particularly facile, and since some of the more activated derivatives are cleaved under conditions which leave benzyl, various ester, and formyl groups unaffected, they have found application in the protection of primary and secondary alcohols. Deprotection with DDQ in dichloromethane/water follows the order 3,4-dimethoxy > 4-methoxy > 3,5-dimethoxy > benzyl and secondary > primary, thus allowing the selective removal of one function in the presence of another. 2,6-Dimethoxybenzyl esters are readily cleaved to the corresponding acids on treatment with DDQ in wet dichloromethane at rt, whereas 4-methoxybenzyl esters are stable under these conditions. Oxidative cleavage of N-linked 3,4-dimethoxybenzyl derivatives with DDQ has also been demonstrated. ... 

Benzyl esters are cleaved by catalytic hydrogenation and also by acidolysis albeit only under fairly drastic conditions. Electron-withdrawing substituents, such as the nitro group in / -nitrobenzyl esters, destabilize the benzyl cation and render the benzyl group even more resistant to acids. In contrast, the action of moderately strong acids, like dilute solutions of HCl in acetic acid or neat trifluoroacetic acid is sufficient for the acidolytic cleavage of /7-methoxybenzyl esters and, of course, of tert.butyl esters. 

Deprotection of Derivatives of Carboxylic Acids.—Methyl esters are demethylated with anhydrous trifluoroacetic acid, in yields ranging from quantitative to 2%. Triarylamine radical cations react with benzyl esters in an oxidative cleavage reaction to give carboxylic acids yields are best with p-methoxybenzyl esters. ... 

Access to derivatives with protecting groups other than benzyl was also desired. Tri-O-acetyl-D-glucal (13) was deacetylated and benzylated with p-methoxybenzyl chloride to give 14. Cleavage of the olefin in 14 gave formate aldehyde 15. Hydrolysis of the formate ester led to lactol 16 and Wittig olefination then furnished the PMB protected olefin alcohol Id (Scheme 3). 

Deprotection. Treatment with AlClj leads to selective cleavage of an isopropyl aryl ether without affecting a coexisting methoxy substituent. A combination with ethanethiol is effective for the deprotection of p-methoxybenzyl ethers. Penicillin esters attached to... 

Bismuth(III) chloride in acetonitrile has been reported as a catalyst for the selective and efficient cleavage of trityl ethers. THP ethers, tert-butyloxicarbonyl (BOC) group, tert-butyldiphenylsilyl (TBDPS) and p-methoxybenzyl (PMB) esters were resistant to these conditions [100]. 

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