Abstract
Abstract The regioselectivity of benzylation of stannylene acetals of trans-diols on pyranose rings is improved by performing the reaction in benzyl bromide, for instance, for methyl 4,6-O-benzylidene-2,3-O-dibutylstannylene-α-D-glucopyranoside, the ratio of 2-O-benzyl ether to 3-O-benzyl ether changed from 70:20 in DMF to 74:8 in benzyl bromide, then improved further to 84:2 if the dihexylstannylene acetal was used. Standard conditions for methylation of stannylene acetals are methyl iodide in DMF. Non-polar conditions give much improved regioselectivity, the O-2 to O-3 product ratio for the above dibutylstannylene acetal changed from 57:30 in DMF to 84:13 with methyl iodide in 1,1,2,2-tetrachloroethane or 90:8 with methyl triflate in chloroform. Examples of benzylation and methylation reactions on different dialkylstannylene acetals on three different trans-diols are included.
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