Methyl selective esterification

Hydrogenation of methyl salicylate gave mostly exs (25) implying that the last double bond to be reduced is often between the two functional groups. Selective esterification of diol (23) with p-bromobenzenesul-phonyIchloride (BsCl) gave (26) which cyclised in strong base. 

In entirely analogous fashion, the selective esterification of various other common disaccharides by other acylating agents was investigated. One notable example is the selective benzoylation of methyl (3-lactoside with benzoyl chloride, which again produced many interesting results that are recorded in a series of papers with Ram... 

Selective esterification of a primary hydroxyl group in the presence of secondary hydroxyl groups also has been achieved with methyl a-D-glucopyranoside. ... 

G. O. Aspinall, and G. Zweifel, Selective esterification of equatorial hydroxyl groups in the synthesis of some methyl ethers of D-mannose, J. Chem. Soc. (1957) 2271—2278. 

Tatsuta s oleandomycin synthesis is based on the construction of the aglycone by coupling of the C1-C7 (131) and Cg-Ci3 (136) segments, which are derived from L-rhamnose and (S)-( + )-methyl 3-hydroxy-2-methylpropionate, respectively, and on the stereo- and regioselective introduction of the two sugar moieties. Methods for selective esterification and for the synthesis of 2-deoxy-a-glycosides were developed in the course of the synthesis. 

An attractive route, which employs the Sharpless oxidation method, dihydoxylates methyl cinnamate with high enantioselectivity. After regio-selective esterification with trimethyl orthobenzoate, the amino-function is introduced via the azide). The desired product is obtained from benzoyl group migration. 

Zeolites have been employed to shift the equilibrium in transesterifica-tions by absorbing smaller molecules [57]. For example, the methyl ester of benzoic acid can be converted into the tertiary-butyl ester by refluxing in tertiary-butanol in the presence of zeolite 5A. Selective esterification of sterically hindered carboxylic acids with alkyl chloroformates over silica bound hexaalkylguanidinium chloride achieves high yields [58]. For example, benzyl 2,4,6-trimethylbenzoate was synthesised from the carboxylic acid and benzyl chloroformate in 96% yield at 120°C. 

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