Glucopyranoside methyl 4,6-O-benzylidene

This class of acylating agents has thus far been but little used in carbohydrate chemistry. However, unimolar benzoylation of methyl 4,6-O-benzylidene-a-D-glucopyranoside, methyl 4,6-O-benzylidene-a-D-altropyranoside, and benzyl 4,6-O-benzylidene-jS-D-galactopy-ranoside with benzoyl cyanide gave good yields of the corre-... 

Monoacylation by use of lipase/trifluoroethyl butanoate systems occurred predominantly at the 2-position of methyl 6-O-butanoyl-a-D-glucopyranoside and at the 4-posidon of methyl 6-deoxy-a-L-glucopyranoside. Methyl 4,6-O-benzylidene-a- and - D-glucopyranoside were preferentially acetylated at 0-2 and 0-3, respectively, by lipase/vinyl acetate Exposure of the galacturono-6,1-lactone triacetate 32 (see Chapter 16 for its synthesis) to wheat germ lipase gave the diacetate 33 in modest yield. ... 

Cyclic sulfates rapidly react with the fluoride ion sources to give monofluoro derivatives Thus, the 2,3-cyclic sulfate of methyl-4 6 O benzylidene p D manno pyranoside cleanly reacts with tetramethylammonium fluoride to give methyl 4,6-0-benzylidene 2 deoxy 2 fluoro-p-D-glucopyranoside-3-sulfate Acid hydrolysis followed by acetylation gives 2 deoxy 2 fluoro-P-D-glucopyranoside triacetate in 84% isolated yield [5S] (equation 38)... 

C44H68012Sn2 Di-//-(methyl 4,6-O-benzylidene-a-D-glucopyranosid-2,3-diyl)bis[dibutyltin(IV)] (BZGBSN)136... 

Ethoxycarbonyl chloride is, by virtue of resonance involving the ester function, less reactive than acetyl chloride, and the reagent has found application for selective O-acylation in the steroid field.34 With this reagent, methyl 4,6-O-benzylidene-a-D-glucopyranoside yielded35 2- and 3-esters in the ratio 24 1, and the related benzyl-thiocarbonyl chloride gave the 2-ester in 58% yield.36... 

Differentiation between the secondary hydroxyl groups in methyl 4,6-O-benzylidene-a-D-glucopyranoside was observed on reaction with methyl benzoate-sodium methoxide at 200° for 45 minutes the 2- and 3-esters and the 2,3-diester were formed176 in the molar ratios of 55 23 10. 

Jenkins, D. J. Potter, B. V. L., On the Selectivity of Stannylene-Mediated Alkylation and Esterification of Methyl 4,6-O-Benzylidene Alpha-D-Glucopyranoside. 

However, for an apparent 0-3 to 0-2 migration of a nitro group during the alkaline methanolysis of methyl 4,6-O-benzylidene-a-D-glucopyranoside 3-nitrate, see J. Honeyman and J. W. W. Morgan,/. Chem. Soc., (1955) 3660-3674. 

The results obtained in the methyl D-glucopyranoside series were thoroughly extended to other benzylidene acetals. From methyl 4,6-O-benzylidene-a-D-galactopyranoside (22), the expected 6-bromo derivative 80 was obtained in high yield (90%),116 and methyl 2,3-di-O-... 

A reagent system consisting of triphenylphosphine/imidazole/iodine in toluene has proven useful for the conversion of trans- 1,2-diols (547) into the corresponding alkenes (549 Scheme 120) (79S469). The imidazole probably forms a solvated complex (548) with triphenylphosphine and iodine. Methyl 4,6-O-benzylidene-a-D-glucopyranoside was transformed into 2,3-dideoxyhex-2-enopyranoside in 75% yield. 

OH-2 and OH-3 in methyl 4-O-methyl-p-D-xyIopyranoside [28] or alkyl 4,6-0-benzylidene-(3-D-glucopyranoside [29] (cf. Ref. [30] for discussion of the discrepancy observed, see Ref. [10]). This preponderance of position 2 over 3 appears also in methyl 4,6-O-benzylidene-a-D-mannopyranoside, the axially oriented hydroxyl group being substantially more reactive than the equatorial one [31-33]. Some 55% of 2-0-benzyl and 19% of 3-Obenzyl derivative have been isolated, together with 10% of 2,3-di-O-benzyl and 16% of the starting material [33]. 

Under the same conditions, the reactivity of hydroxyl groups is OH-2 > OH-3 for methyl 4,6-O-benzylidene-a-D-glucopyranoside, and OH-3 > OH-2 for the P-ano-mer [48] or for the corresponding galactopyranoside [49]. The hydroxyl group in position 2 is the most reactive in sucrose benzylation [27]. It seems that the cis-OR substituent activates the adjacent equatorial hydroxyl group [33] in benzylations in the presence of barium oxide. 

J. C. Lopez, E. Lameignere, and G. Lukacs, Stereospecificity in Diels-Alder reactions of dienes and dienophiles derived from methyl 4,6-O-benzylidene-a-D-glucopyranoside, J. Chem. Soc., Chem. Commun., (1988) 706-707. 

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