Glucose dimethyl acetal, crystalline

The relative reactivity toward sodium of the hydroxyl groups at the various carbon atoms of a sugar has been exploited in order to prepare selected derivatives. By the addition of one molar equivalent of sodium to 4,5-0-isopropylidene-D-fucose dimethyl acetal in ethyl ether, followed by benzyl chloride, Schmidt and Wernicke were able to isolate a 42 % yield of 2-0-benzyl-4,5-0-isopropylidene-D-fucose dimethyl acetal. Freudenberg and Noe reacted molar equivalents of 1,2-0-isopropylidene-a-D-glucofuranose and sodium in boiUng dioxane. Subsequent reaction with benzyl chloride, and acetylation, gave a 29 % yield of crystalline 5,6-di-0-acetyl-3-0-benzyl-1,2-0-isopropylidene-a-D-glucose. 

Proof of Constitution.—Reference to Table XII will show that all of the methods mentioned above as being suitable for the synthesis of 4,6-dimethylglucose have been correlated by means of crystalline derivatives. If the tosyl, benzyl and nitrate radicals can be regarded as being non-migratory (and there is no evidence to the contrary) then the course of the synthesis from 4,6-acetals (the constitution of which has been proved by their conversion into 2,3-dimethyl-D-glucose) leaves no doubt that the methyl groups occupy positions 4 and 6. 

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