Carbohydrate allyl ether, preparation

In carbohydrate chemistry, the preparation of ethers that are stable in the presence of acids, bases, and aqueous alkali is an important analytical and synthetic tool. The methods used for the etherification of hydroxyl groups51 generally employ reactions of unprotected sugars and glycosides with methyl, allyl, benzyl, triphenylmethyl, and alkylsilyl halides in the presence of a variety of aqueous and nonaqueous bases. 

Many other ethers of carbohydrates have been prepared and described among these the more common additional ones are the following ethyl, benzyl, hydroxymethyl, hydroxyethyl, allyl, and cyanoethyl ethers. In the vast majority of the cases complete or nearly complete substitution of the hydroxyl groups was effected. In other instances partial substitution was obtained, but often little or no information was supplied concerning the location of substituents. Investigations of these types will be mentioned briefly, in order mainly to indicate the extent of the information that is available. 

The allyloxycarbonyl group [269] has shown a wide application in organic synthesis, especially in the fields of peptides, nucleotides, and carbohydrates. Allyloxycarbonyl derivatives are more easily prepared than the corresponding allyl ethers and they are more stable than ester protecting groups which find frequent use in carbohydrate chemistry. 

Carbohydrate allenyl ethers have been prepared via the corresponding propargyl ethos,and sucrose 0-octadienyl ethers have been synthesized by a novel telomerisation of butadiene with sucrose in the presence of Pd(acac>2 and PhsP. Radical bromination of allyl ethers using MBS in CCU in the presence of isopropylidene acetals, acetates and benzoates has allowed the selective removal of the allyl ethers with a hydrolytic work-up. ... 

Other Alkyl and Aryl Ethers. - The reagent system of allyl ethyl carbonate and a Pd(0) catalyst, applied to carbohydrate alcohols, has been utilised for making allyl ethers under neutral conditions. The synthesis of benzyl ethers from the parent alcohols under non-basic conditions has been achieved using phenyldiazomethane and HBF4. Dibutylstannylene compounds derived from benzyl -D-lactoside and its derivatives have been regioselectively benzylated. ° Similarly, 2,2 -di-0-alkyl-4,6 4 6 -di-0-benzylidene-Qt,a-trehaloses have been prepared by regioselective alkylation of a dibutylstannylene derivative. Phase transfer catalysed benzylation... 

Carbohydrates remain an attractive source of chirality in preparation of ligands for asymmetric catalysis. Functionalized phospholanes, 192 [167], and chiral bisphosphinites 193 [168] with an attached crown ether unit were obtained recently from D-mannitol and from phenyl 2,3-di-0-allyl-4,6-0-benzylidene-p-D-glucopyranoside, respectively (Figure 18). Compounds 194 and 195 were obtained in the photochemical addition of H2P(CH2)3PPH2 onto the crresponding alkenes - Pd-complexes of these new bisphosphines were successfully applied as catalysts in the copolymerization of CO and... 

Other Alkyl and Aryl Ethers. - The preparation of selectively 0-alkylated saccharides, including benzyl, allyl, triphenylmethyl, and arylalkyl ethers has been reviewed. Analogues of lipids A and X incorporating 3-O-alkyl (rather than acyl) linkages have been described, and some carbohydrate monoalcohol derivatives have been alkylated with haloacetic acid ester derivatives. ° 3-C -Carboxymethyl D-glucose and D-fhictose compounds have been coupled via the carboxylic acid group to L-lysine in a search for acrosin inhibitors."... 

Methyl Ethers. - Several polyhydroxy carbohydrate derivatives have been efficiently 0-methylated using the system 50% aq Na OH, DMSO, Mel. A number of mono-0-methyl ethers of the trimannose oligosaccharide a-o-Manp-(l->3)-[a-D-Man p-(l-+6)]-P-D-Manp-0-C8Hi7 have been prepared. Allyl 2-acetamido-2-deoxy-3-0-P-D-galactopyranosyl-6-0-methyl-a-D-galactopyranoside has been synthesized as a potential acceptor for a sulfotransferase, while mono-2-0-methyl-cyclomaltoheptaose was formed by methylation of cyclo-maltoheptaose in dilute aqueous alkali. ... 

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