Allylic Rearrangements of Glycals

The Lewis acid-mediated allylic rearrangement of glycals like 28 to glycosides 29 known as the Ferrier-reaction is well known in carbohydrate chemistry [14-16]. It yields predominantly a-configurated hex-2-enopyranosides (cf. 29), either in the d-or L-sugar series. These may be hydrogenated to glycosides like the 2,3,6-trideoxy-species 30. 

R. Blattner, R. J. Ferrier, and R. H. Furneaux, Intervention of catalytic amounts of water in the allylic rearrangement of glycal derivatives, Tetrahedron Asymmetry, 11 (2000) 379-383. 

Allylic rearrangements of glycal esters continue to be used] dl- -acetyl-D-xylal afforded 2,3-unsaturated glycosyl azides together with the Isomeric 3-azldo-3-deoxyglycal eplmers on treatment with sodium azide in the presence of boron trifluoride. The latter, on azldonltration, afforded routes to 2,3-dlamlno-2,3-... 

Several additional reports have appeared on the use of unsaturated compounds in the synthesis of C-glycosides. The allylic rearrangement of glycal derivatives continues to receive attention. Tri-O-acetyl-D-glucal, treated with allyltrlmethylsilane, 1,2-bis(trimethyIslly1)acetylene and furan in the presence of Lewis acid catalysts, gives compounds ( 9) - (51) respectively (51) was obtained with an equal proportion of the isomer (52), which Is an... 

As already mentioned, unsaturated sugars, particularly glycals, are readily available compounds. Perrier rearrangement of glycals in the presence of Lewis acids and alcohols easily takes place to provide 2,3-unsaturated carbohydrates. The allylic esters obtained this way can be engaged in different reactions with organometallic reagents. 

TABLE 37.4. Ferrier Rearrangement of Glycal Allylic Ethers... 

Perrier RJ (2001) Substitution-with-Allylic-Rearrangement Reactions of Glycal Derivatives. 215 153-175... 

Tochtermann reported the addition of dichlorocarbene to the racemic glycal 52, whose cyclopropyl-allyl rearrangement leads to the 2//-pyran. The synthesis of the optically pure (+)-(2S,3R,7S) and (-)-(2f ,3S,7f )-glycal precursors has also been achieved. As pointed out, optically pure glycals are versatile precursors for carbohydrate synthesis <00EJO1741>. 

In order to simplify these preparations, Boivin et al. [52] made use of the allylic rearrangement reaction (Ferrier type) which was one of the first accesses to 3-amino glycals. By use of azide as the nucleophile, the L-arabino configurated glycal 78... 

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