The secondary hydroxyl groups in methyl 4,6-0-benzylidene-/3-Dglucopyranoside
(1) show i, towards various reagents, little selectivity in partial etherification and esterification reactions, compared to those in the corresponding cr-D-glucopyranoside derivative. Most of the selective benzylatiorG, methylation2,3, benzoylation4-6, and sulfonylation5p7 reactions of 1 attempted give the 2-and 3monosubstituted derivatives in poor to moderate yields, because of (a) simultaneous formation of the 2,3-disubstituted derivatives in substantial proportions and (b) rather high recovery of unchanged starting-material 1. Regioselective benzylatiorP and p-toluenesulfonylation9 of 1, using phase-transfer catalysis, were reported to give good yields of the 2-benzyl ether 3 and 2-sulfonate 13, respectively.
Recently, David et LzL~OJ~ developed mild and efficient procedures for the regioselective benzoylationrO and alkylation" of several derivatives of D-gluco-and D-galacto-pyranosides via the dibutylstannylene derivatives, and these methodslOJ1
were extended to the selective alkylation1*J3 and benzoylation13 of the diol derivatives of glycosides of L-fucosel* and 6-deoxy-r_-talose13. The application of these procedureslOJ1 to the regioselective benzylation, allylation, methylation, benzoylation, and p-toluenesulfonylation of 1 is now described. The results obtained with the regioselective reactions of 1 via the 2,3-O-dibutylstannylene derivative 2, prepared by azeotropic remova110J1,13 of water from a mixture of 1 and dibutyltin oxide in benzene, are shown in Table I. Alkylation of 2 with benzyl bromide or ally1 bromide in boiling benzene, in the presence of tetrabutylammonium bromide", afforded high yields (-90%) of the 2-(3) and 3-benzyl (4) ethers and of the 2-(5) and 3-ally1 (6) ethers, respectively; no 2,3-diethers were formed and no starting material 1 remained. Under conditions similar to those used for the benzylation and allylation of 2, there was no reaction of 2 with methyl iodide, whereas treatmentlO of 2 with methyl iodide in N,N-dimethylformamide led *To whom enquiries should be addressed.