1.2- Unsaturated C-glycoside

P. Tiwari, G. Agnihotriand, and A. K. Misra, Synthesis of 2, 3-unsaturated C-glycosides by HC104-Si02 catalyzed Ferrier rearrangement of glycals, Carbohydr. Res., 340 (2005) 749-752. 

J. Herscovici, S. Delatre, and K. Antonakis, Enantiospecific naphthopyran synthesis by intramolecular Diels-Alder cyclisation of 4-keto 2,3-unsaturated C-glycosides, Tetrahedron Leu. 32 1183 (1991). 

Two groups have reported on the use of the Claisen rearrangement to obtain 2,3-unsaturated C-glycosides. Fraser-Reid and colleagues found the standard reaction applied to derivatives of the allylic alcohol (77) inefficient because of the poor yields of the derived vinyl ethers or because allylic esters e.g. (78) predominated. They were successful, however, in obtaining compounds (79) and (80) by modified procedures (Scheme 5). An alternative synthesis of saturated, and hence unsaturated, C-glycosides was developed as illustrated in Scheme 6. In parallel work Ireland and co-workers used the enol silyl ether approach as shown in Scheme 7 and employed the products in polyether antibiotic syntheses. ... 

Several examples have been reported of the synthesis of 2,3-unsaturated C-glycosides by application of the Lewis-acid catalysed rearrangement condensation with acylated glycals. These are Illustrated in Scheme 25 a more complex reaction of a related kind is shown in Scheme 26. An alternative route to 2,3-unsaturated C-glycosides Involves a C3,3]-sigmatropic rearrangement... 

Ireland and his co-workers have amplified their studies on the synthesis of furanoid and pyranoid glycals (Scheme 1) and their use in the synthesis of 2,3-unsaturated C-glycosides (see Chapter 3). ... 

As is to be expected from the above, vinyl ethers or esters react with glycals in standard rearrangement processes to yield 2,3-unsaturated C-glycosides,tri-0-acetyl-D-glucal with enol acetates [70] or enol silyl ethers [71] of acetaldehyde, acetone and acetophenone giving access to the carbonyl compounds 49 (R = H, Me, Ph), respectively. 

Chem., 1983, 61, 533). A large range of 2,3-unsaturated C-glycosides have been made in good yields from glycal and "2-hydroxyglycal" esters and alkenes as exemplified in Scheme 21. Related rearrangements are illustrated in Scheme 22, the anomeric... 

Several other chapters refer to the use of 2,3-unsaturated pyranoid substances in synthesis in Chapter 3,and in the earlier part of this Chapter,2,3-unsaturated C-glycosides are noted and further... 

For the synthesis of 2,3-unsaturated C-glycosides with carbonyl groups at C-3 of the C-1 substituents the use of allyl silyl ethers together with a Lewis acid catalyst is recommended [74]. 

A good method for making 1-C-arylated glycals involves the use of the iodo-compound (155) (Scheme 39), and the 3-deoxyglycal (156), together with palladium acetate, can be used to make 2,3-unsaturated C-glycosides (Scheme 40). ... 

Unsaturated C-glycosides can be made by direct substitutions applied to other 2,3-unsaturated compounds. Thus, phenyl glycosides treated with ethyl nitroacetate, trlphenylphosphine and... 

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