C-Pyranosides

The rearrangement provides a stereocontrolled synthesis of the C-pyranoside 2, present in pseudomonic acids.2... 

D. Crich and L. B. L. Lim, Diastereoselective free-radical reactions, part 2. Synthesis ol 2-deoxy-p-C-pyranosides by diastereoselective hydrogen-atom transfer, J. Chem. Soc. Perkin Trans. 7 2205 (1991). 

The methods described thus far represent only a small subset of the available techniques for the formation of C-furanosides and C-pyranosides. Other useful methods include cyclizations of halo olefins and ene-ynes [224] and the direct modification of pyran ring systems [251]. Although not discussed further here, these examples are mentioned to illustrate the breadth of work accomplished in this area. 

Perrier, R J, Petersen, P M, Unsaturated carbohydrates. Part 31. Trichothecene-related and other branched C-pyranoside compounds, J. Chem. Soc., Perkin Trans. 1, 2023-2028, 1992. 

Beau, J M, Sinay, P, Preparation and reductive lithiation of 2-deoxy-D-glucopyranosyl phenyl sulfones a highly stereoselective route to C-glycosides, Tetrahedron Lett., 26, 6185-6188, 1985. Crich, D, Lim, L B L, Synthesis of 2-deoxy-(3-C-pyranosides by diastereoselective hydrogen-atom transfer. Tetrahedron Lett., 31, 1897-1900, 1990. 

Burke, S D, Armistead, D M, Schoenen, F J, Fevig, J M, An enolate Claisen route to C-pyranosides. Development and application to an ionophore synthon. Tetrahedron, 42, 2787-2801, 1986. 

As shown in Scheme 7.3.1, Frick, etal.,13 formed the perbenzylated polyol on treatment of the lithiated flavonoid with the ring opened form of penta-O-benzylglucose. As illustrated, catalytic hydrogenation in acetic acid produced a C-furanoside after three hours and a C-pyranoside after two days. Additionally,... 

The use of nucleophilic carbohydrates for the synthesis of C -pyranosides has been extended to include glycosyl-lithium (36 M = Li) which is generated under standard conditions from the corresponding stannane (36 M = SnBu )- The B-anomer of (37 M = SnBu ) is also available and both lithiated derivatives have been shown to be configurationally stable. 

The preparation of the branched C-pyranoside 27, which is structurally related to trichothecenes, has been carried out by treatment of the thionoformate 28 (prepared in several steps from 2,3,4,6-tetra-0-acetyl-2-hydroxy-D-glucal) with tributyltin hydride. Also described are the tricyclic compounds 29, prepared from an intermediate used for the synthesis of 27. 

Fig. 1 Various representations of the monosaccharide Glucose (a) extended Fischer projection (b) Haworth projection (c) pyranoside Cj chair representation (d) 3D conformational representation. The numbers indicate the standard designations of each carbon atom in the monosaccharide. This numbering is also used to identify the OH groups, OHn being the OH group bound to Cn...

In a similar fashion the same authors have described the synthesis of disubstituted cyclopropa[c]pyranosides (Scheme 26)/ Several examples are given. 

C-Glycosides are increasing in importance, and the synthesis of several 2,3-unsaturated C-pyranosides produced by allylic rearrangement reactions of glycals are referred to in Chapter 3. 

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