Applications of boron trichloride in carbohydrate chemistry

Abstract

The reactions of boron trichloride and boron tribrormide with a wide variety of carbohydrate and polyol derivatives have been investigated. These boron halides were used for the deacylation and dealkylation of mono-, di- and polysaccharides, the last two types being converted into the monosaccharide constituents. Similarly boron trichloride effected the fission of triphenylmethyl ethers giving the parent monosaccharide or polyol. however, tolueno-p-sulphonic esters were found to be stable to treatment with boron trichloride. With the exception of D-fructose and L-sorboseall the monosaccharides which were investigated were stable to treatment with boron trichloride and boron tribronide. D-fructose and its derivatives wereconverted into 5-hydroxymethylfurfuraldehyde, which was isolated and characterised.In general unsubstituted disaccharides were not attacked by boron trichloride, but were cleaved by boron tribromide to give the constituent monosaccharides or 5-hydroxymethylfurfuraldehyde if fructose units were present. Cyclic acetals and ketals, glycosides and 1,6-anhydro hexoses all gave the parent monosaccharide on treatment with boron trichloride, However, 2,3-anhydro sugars appeared to give chlorodeoxy derivatives. Boron trichloride was found to have applicationas a synthetic agent also. The complex obtained bytreatment of methyl a-D-glucoside with borontrichloride was a successful glucosylating agent. Oncondensation with alcohols and phenols, D-glucose and benzene, glucosides, disaccharides andglucopyranosylbenzene were obtained. Of the eleven possible glucose disaccharides all except the three trehaloses were isolated and characterised. A mechanism was proposed for reactions of this type.