L,2:5,6-Di-0-Isopropylidene-D-glucose

Despite the immediate application of unimolar sulfonylation for the preparation of many w-sulfonic esters of sugar derivatives, a kinetic study of the reaction was not made until 1942 Hockett and Downing136 then found that, with p-toluenesulfonyl chloride-pyridine at 23° 2°, the time to half-esterification for a mole of l,2 3,4-di-0-isopropylidene-D-galactose (with a primary hydroxyl group) is 0.272 hours (see Fig. 2), whereas for l,2 5,6-di-0-isopropylidene-D-glucose (with a secondary hydroxyl group) it is 20.2 hours (see Fig. 3). That is, after about 120 minutes, nearly all of the compound with the free primary hydroxyl group... 

In another approach, a glucose-derived titanium enolate is used in order to accomplish stereoselective aldol additions. Again the chiral information lies in the metallic portion of the enolate. Thus, the lithiated /m-butyl acetate is transmetalated with chloro(cyclopentadienyl)bis(l,2 5,6-di-0-isopropylidene- -D-glucofuranos-3-0-yl)titanium (see Section I.3.4.2.2.I. and 1.3.4.2.2.2.). The titanium enolate 5 is reacted in situ with aldehydes to provide, after hydrolysis, /i-hydroxy-carboxylic acids with 90 95% ee and the chiral auxiliary reagent can be recovered76. 

The problem is to differentiate these two hydroxy groups from the 5- and the 3-hydroxy-functions. To this end D-glucose is converted into the well-known l,2 5,6-di-0-isopropylidene-D-glucofuranoside (1), in which the 3-hydroxy group only is unprotected, and thus may be... 

In l,2 5,6-di-0-isopropylidene-a-D-glucofuranose five of the six funaional groups of glucose are protected. The free 3-hydroxyl group is a popular starting point in synthesis. It... 

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. 

Soon after the application of sulfonylation to sugar derivatives, the action of hydrazine17 on l,2 5,6-di-0-isopropylidene-3-0-tosyl-D-glucose, and of ammonia297 on l,2 3,4-di-0-isopropylidene-6-0-tosyl-D-galactose, was found to proceed similarly. Immediate application of this principle to preparation298 of aminated cellulose derivatives,86299 of possible... 

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