Benzoates selective esterification

The 2,4-Q-dibutylstannylene acetal of 1,6-anhydro- -D-glucopyranose has been used to effect selective esterification and alkylation to give the 4-Q-benzoate (55%) and 4-Q-benzyl ether (40%) preferentially, but separation from the 0-2 substituted isomer was... 

Esterification of several methyl 4,6-O-benzylidene-D-hexo-pyranosides with one molar equivalent of benzoyl chloride-triethylamine in an inert solvent was found to occur with good selectivity, mainly affording 2-benzoates from the a-D-gluco, a-D-allo, and a-D-altro compounds, and the 3-benzoate from the j8-D-gluco compound.52... 

AcCl, Ag20, cat. KI, CH2CI2,40°C, 60-99% yield. In some cases, this method gives results that are complementary to the stannylene method. Selectivity, in the esterification is dependent upon the configuration at the anomeric position of a pyranoside. Benzoates give similar results, but with tosylates the regiose-lectivity is reversed in some cases. 

Moving in the other direction, pivaloate (Pv, Piv) esters are heavily deactivated with respect to acetates which results in high selectivity during esterification and low reactivity towards the conditions routinely used for acetate and benzoate... 

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