Ethylidene glucose

Butylethylidene and 1-phenylethylidene ketals were prepared selectively from the C4-C6, 1,3-diol in glucose by an acid-catalyzed transketalization reaction [e.g., Me3CC(OMe)2CH3, TsOH/DMF, 24 h, 79% yield PhC(OMe)2Me, TsOH, DMF, 24 h, 90% yield, respectively]. They are cleaved by acidic hydrolysis AcOH, 20°, 90 min, 100% yield, and AcOH, 20°, 3 days, 100% yield, respectively. Ozonolysis of the /-butylmethylidene ketal affords hydroxy ester, albeit with poor regiocontrol, but a more sterically differentiated derivative may give better selectivity, as was observed with the ethylidene ketal. ... 

Figure 13 Distinction of the anomeric centre of 4,6-O-ethylidene-D-glucose using RDCs. (A) a and (i isomers are easily distinguished from RDCs at position Cl. (B) The two anomeric forms with corresponding RDCs. (Adapted with permission from ref. 148. Copyright 2003 American...

A second monoethylidene-D-sorbitol (m. p. 98-100°), the 4,6-isomer, has been reported recently by Hockett, Collins and Scattergood.142 It was derived from 4,6-ethylidene-D-glucose by hydrogenation in slightly alkaline solution and consumed two molecular equivalents of lead tetraacetate.142... 

Kircher [399] also described the GC analysis of acetals, in addition to the above-mentioned derivatives (see p. 166). He demonstrated the analysis of 4,6-O-ethylidene-D-glucose in the form of the 1,2,3-triacetate on a column packed with completely methylated hydroxyethylcellulose. The diisopropylidene derivative of glucose (retention time ca. 50 min at 200°C) was sufficiently volatile for the analysis and its methyl, ethyl and vinyl ether in the 3-position was even more volatile (retention time 16 min). Mutual separations of these derivatives have not been achieved, however, on this column. 

The introduction of the phosphonate grouping into a sugar molecule (see Section III, 3 p. 260) has been further investigated by Paulsen and coworkers.97 Thus, the phosphonate phosphorane 120a was shown to react with 2,3,4,5,6-penta-O-acetyl-a/dehydo-D-glucose, 2,3 4,5-di-0- isopropylidene - aldehydo - D - arabinose, and 2,4-0-ethylidene-a/dehi/do-D-erythrose, leading to the unsaturated phos-phonates 229, 230a, and 231, respectively, in moderate yields. 

Benzylidene acetals are frequently used for the protection of the 4- and 6-hydroxyl groups of pyranoses, Reclamation of the diol can be accomplished by many methods that will be discussed below, but Scheme 3.53 shows an unusual cleavage of benzylidene acetals protecting the glucose moieties in 53.1 using 1% iodine in methanol (w/v),86 The reaction works equally well with isopropylidene, ethylidene and dithioacetals,87... 

B. (-)-2,4-O-Ethylidene-D-erythrose. A 1-L, three-necked, round-bottomed flask, equipped with a thermometer and two 200-mL pressure-equalizing dropping funnels, is charged with a suspension of sodium metaperiodate (59.2 g, 27> mmol, Note 11) in water (450 mL). The flask is cooled to 0°C using an ice-water bath. A solution of (-)-4,6-O-ethylidene-D-glucose (29.2 g, 142 mmol, Note 12) in water (120 mL) is added dropwise with stirring and under permanent control of the pH (Note 6) and... 

The 3-methyl ethers of the 4,6-0-benzylidene and 4,6-0-ethylidene derivatives of methyl 2-(A-benzyloxycarbonyl)amino-2-deoxy-a-n-gluco-pyranoside have been prepared by a sequence of reactions paralleling Neuberger s synthesis. The d anomer of the latter compound was obtained directly by methylation of 2-(A-benzyloxycarbonyl)amino-2-deoxy-4,6-0-ethylidene-D-glucose with dimethyl sulfate and alkali. Both anomers were transformed into the free amines by catalytic hydrogenolysis. ... 

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