Fucose 2-benzyl ether

Maher, George G., The Methyl Ethers of the Aldopentoses and of Rhamnose and Fucose, X, 257-272 Maher, George G., The Methyl Ethers of D-Galactose, X, 273-282 Manners, D. J., The Molecular Structure of Glycogens, XII, 261-298 Marsh, C. A. See Conchie, J. McCloskey, ChesterM., Benzyl Ethers of Sugars, XII, 137-156 McColloch, R. J. See Kertesz, Z. I. McDonald, Emma J., The Polyfructo-... 

Schmidt and Wernicke74 have described a synthesis of digitalose starting with D-fucose dibenzyl mercaptal, which on condensation with acetone yielded the 4,5-isopropylidene derivative (LXXIV). Elimination of the dibenzyl mercaptal residues with mercuric chloride and cadmium carbonate in methanol gave 4,5-isopropylidene-D-fucose dimethylacetal (LXXV), from which the 2-benzyl ether was obtained on treatment with sodium and benzyl chloride. Methylation produced 2-benzyl-3-methyl-4,5-iso-propylidene-D-fucose dimethyl acetal (LXXVI), from which the iso-propylidene group was eliminated on treatment with methanolic hydrogen chloride, which also effected glycopyranoside formation (LXXVII). The... 

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. 

In a final example demonstrating the utility of unfunctionalized olefins, Levy, et al.,43 reported a novel adaptation in which the formed C-glycoside cyclizes to an adjacent oxygen with loss of a benzyl group. As shown in Scheme 2.3.17, l-0-acetyl-2,3,4-tri-0-benzyl-L-fucose was treated with isobutylene and an excess of TMSOTf giving the illustrated fused ring C-glycoside. This reaction proceeded in >70% yield in both methylene chloride and acetonitrile. Additionally, borontrifluoride etherate could also be used. The proposed mechanism, shown in Scheme 2.3.17, involves the initial elimination of the... 

In exploring the generality of this reaction, the 1-O-acetyl-tetra-O-benzyl analogs of D-glucose, D-galactose, and D-mannose, were studied. In all three cases, borontrifluoride etherate was found to be too weak a Lewis acid to effect this reaction and TMSOTf was required. The reactions of these compounds with TMSOTf and isobutylene are summarized in Table 2.3.1. An additional example with L-fucose and methylene cyclohexane is also included therein. 

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