4,6-0-Benzylidene glucose

The old condensation38 of 4,6-O-benzylidene-D-glucose with nitromethane in the presence of sodium methoxide to give D-heptitol 42 and cyclic nitromethyl p-D-glucopiranose (44, 5% yield) has recently been revisited. 

Primary alcohol groups in several protected ribo-, fructo- and glucofuranoses including 2,3,4-tri-O-benzoyl-D-glucose, 1,2-isopropylidene-D-xylo-furanose, 2,3 4,5-di-0-isopropylid-ene-D-fructopyranose, methyl 2,3-O-isopropylidene-P-D-ribofuranoside, l,2-0-isopropylidene-3,5-0-benzylidene-D-glucofuranose and... 

Acetalation. As polyhydroxy compounds, carbohydrates react with aldehydes and ketones to form cyclic acetals (1,13). Examples are the reaction of D-glucose with acetone and a protic or Lewis acid catalyst to form l,2 5,6-di-0-isopropylidene-a-D-glucofuranose [582-52-5] and its reaction with benzaldehyde to form 4,6-O-benzylidene-D-glucopyranose [25152-90-3]. The 4,6-0-(l-carboxyethylidine) group (related to pyruvic acid) occurs naturally in some polysaccharides. 

T. J. Tewson and M. Soderlind, I-Propenyl 4,6-0-benzylidene-g-i>mannopyranoside-2,3-cyclic sulfate A substrate for the synthesis of [F-18] 2-deoxy-2-fluoro-n-glucose, J. Carbo-hydr. 4 529 (1985). 

In contrast to that of glucose, the hydroxyl group at position 3 of D-galactopyranose derivatives is more reactive than that at position 2. Thus, tosylation160 of methyl 4,6-0-benzylidene-a(or -/8)-D-galactoside gives a preponderance of the 3-O-tosyl derivative admixed161-163 with a little of the 2-O-tosyl and 2,3-di-O-tosyl derivatives. 

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