Carbon-disaccharide, synthesis

Another mode of carbon-based activation of hemiacetals relies on carbonyl-centered electrophiles 89 (Scheme 3.14). These reagents have demonstrated the highest efficiency for disaccharide synthesis among electrophilic carbon activating agents. In the event, the hemiacetal 1 is activated with electrophile 89 for in situ... 

Y. Wang, S. A. Babirad, and Y. Kishi, Preferred conformation of C-glycosides. 8. Synthesis of 1,4-linked carbon disaccharides, J. Org. Chem. 57 468 (1992). 

To complete the synthesis of keto disaccharide 16, the cyclic carbonate must be cleaved and the C-4 hydroxyl group must be oxidized selectively. With respect to the former objective, it is well known that a metal alkoxide (e. g. sodium methoxide) can easily... 

R. R, Schmidt and R. Preuss, Synthesis of carbon bridged C-disaccharides, Tetrahedron Lea. 30 3409 (1989) B. Giese, M. Hoch, C. Lamberth, and R. R. Schmidt, Synthesis of methylene bridged C-disaccharides, Tetrahedron Lett. 29 1375 (1988). 

H. A. Nunez and R. Barker, Enzymalic synthesis and carbon-13 nuclear magnetic resonance conformational studies of disaccharides containing fJ-D-galactopyranosyl and p-D-[l-13C]galacio-pyranosyl residues, Biochemistry 19 489 (1980). 

In early work [165] on the synthesis of the pentasaccharide (236), the azide (237) was condensed with (238) [an intermediate in the preparation of (237)]in the presence of silver perchlorate and polyvinylpyridine to give the a-linked disaccharide (239) in 60 % yield and this on acetolysis gave the disaccharide (240) which contains the potential terminal disaccharide unit of the Forssman antigen. Compound (240) was converted into the glycosyl bromide with titanium(IV) bromide under carefully controlled conditions [182] and condensed with l,6-anhydro-2,4-di-0-benzyl-D-galacto-pyranose in the presence of silver carbonate to give the potential terminal trisaccharide (241) of the Forssman antigen. 

Among the available methods to synthesize fused-ring thietes and bi- or tricyclic thietanes (but not spiro-com-pounds), the most efficient method seems to be the synthesis from acyclic precursors with the same number of carbons. Photocyclization reactions lead to thietes and thietanes in satisfactory to high yields. Mono- and disaccharides bearing fused thietane moieties have been synthesized using this method. 

Reductive metallation must now be performed at room temperature for the electron transfer to proceed at a reasonable rate and under Barbier conditions. At this temperature, the intermediate reagent is stable enough for a carbon-carbon bond formation in the presence of the carbonyl compound (Barbier conditions) because without the latter, it would -eliminate or protonate. This simple procedure is mild enough to be extended to the synthesis of a carbon-linked disaccharide, as shown in Figure 17, for the preparation of the derivative of the C-linked mimic 24 of the a-D-marmopyranosyl(l->2)-D-glucopyra-noside from sulfone 22 and aldehyde 23. ... 

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