Allyl ethers of carbohydrates

Allyl Ethers of Carbohydrate. A number of compds, such as allyl glycerol, allylglycol, allyl mannitol, allylsorbitol, all yl pent a-erythritol, etc were prepd during and after WWII by Nichols Yanovsky. They also discussed previous work on this subject and listed several refs. According to them the first compd of this type was triallyl-glycerol prepd in 1856 by M.Berthelot S. de Luca... 

Protection of hydroxyl groups Benzyl or allyl ethers of carbohydrates are obtained in satisfactory yield by reaction with 1 or 2 in cyclohexane in the presence of triflic add (20°). Trichloroacetamide precipitates and the desired ethers are obtained from the filtrate after neutralization. 

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 use of allyl ethers for the protection of alcohols is common in carbohydrate literature because allyl ethers are generally compatible with the various methods... 

The competition between a propargylic ether and a teriary propargyhc amine provided an allenyl ether rather than an allenylamine [182], The reaction was also successful with propargyl allyl ethers [232]. An additional ester group in the propargylic position is tolerated [233], and consequently the reaction also works with esters of propargyhc alcohols [234—236]. In the past 4years, several derivatives of carbohydrates were converted successfully [217, 237-241] two examples are the isomeriza-tions of enantiomerically pure 98 [242] and 100 [217, 243] (Scheme 1.43). 

N. Moufid and Y. Chapleur, Radical cyclization of allyl propargyl ethers and acetals application to the stereocontrolled acylation of carbohydrates, Tetrahedron Lett. 32 1799 (1991). 

Efforts to cause the carbon nucleophile available at C-2 (carbohydrate numbering) of the osulose derivative 66 to displace the methoxy group with allylic rearrangement and with consequent formation of a tricyclic product by use of Pd(0) catalysts [34] were unsuccessful, but the intended reaction proceeds "smoothly when tin(IV) chloride is used together with acetic anhydride in dichloromethane. Clearly, the Lewis acid activates the allylic ether group, and the C-2 nucleophile effects its displacement. Concurrently, acetolysis of the benzylidene ring occurs and the product isolated is the cu-decalin analogue 67 [33],... 

Allyl carbonates can be cleaved by nucleophiles under palladium(O) catalysis. Allyl carbonates have been proposed for side-chain protection of serine and threonine, and their stability under conditions of /VT moc or /V-Boc deprotection has been demonstrated [107]. Prolonged treatment with nucleophiles (e.g., 20% piperidine in DMF, 24 h) can, however, lead to deprotection of Alloc-protected phenols [108,109]. Carbohydrates [110], tyrosine derivatives [107], and other phenols have been protected as allyl ethers, and deprotection could be achieved by palladium-mediated allylic substitution (Entry 9, Table 7.8). 9-Fluorenyl carbonates have been used as protected intermediates for the solid-phase synthesis of oligosaccharides [111]. Deprotection was achieved by treatment with NEt3/DCM (8 2) at room temperature. 

Methods now available for the partial protection of carbohydrate hydroxyl groups by alkylation are critically evaluated. Of the numerous alkyl protecting groups known, only those widely used in synthetic chemistry of saccharides are discussed. Benzyl, allyl, triphenylmethyl and other arylalkyl ethers, trimethylsilyl, rer/-butyidimethylsilyi, and rm-butyldiphenylsilyl ethers are the main topics of the article. 

P. A. Gent, R. Gigg, and A. A. E. Penglis, The allyl ether as a protecting group in carbohydrate chemistry. Part 9. Synthesis of derivatives of 1,6-anhydro-jS-D-galactopyranose, J. Chem. Soc., Perkin Trans. 1, (1976) 1395-1404. 

Similar utilization for cleavage of benzyl alcohols, ethers and esters has made this method the preferred one where regioselectivity is required, but for allylic cleavage double bond isomerization becomes a problem. A number of benzylic ethers and alcohols (equation 13), and benzhydric ethers and acetals (equation 14) have been cleaved in relatively high yield using cyclohexene in the presence of AlCb. Mild conditions of cleavage are frequently required for debenzylation of carbohydrates and a number of protected carbohydrates have been cleaved with formic acid as donor (equation 15). ... 

Dahlen, A, Sundgren, A, Lahmann, M, Oscarson, S, Hilmersson, G, Sml2/water/amine mediates cleavage of allyl ether protected alcohols — application in carbohydrate synthesis and mechanistic considerations, Org. Lett, 5, 4058-4088, 2003. 

Eshelman, J E, Epps, J L, Kalhnerten, J, Diastereoselective [2,3] Wittig rearrangement of carbohydrate-derived tertiary allylic ethers. 1. Synthesis of the C11-C18 subunit of herbimycin a from D-glucose, Tetrahedron Lett., 34, 749-752, 1993. 

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. 

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