Rearrangements of glycals

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. 

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. 

The drawback of this method arises from the rearrangement of glycals, under the acidic conditions of the reaction, to the 2,3-unsaturated enoses (Ferrier reaction). The other problem is the incompatibility of some acid-labile protective groups with the relatively strong reaction conditions. These difficulties led to the development of different methodologies with the aim of minimizing the... 

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. 

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. 

One of the most convenient methods for the synthesis of 2,3-unsaturated sugars is the so-called Ferrier-I rearrangement of glycals (O Scheme 6). This reaction allows one to obtain the unsaturated targets via the process in which the double bond migrates from the C1-C2 to the C2-C3 position [1,2,4,5,11],... 

The 1,4] rearrangement of glycal 23 derived from D-glucose has been applied in the synthesis of streptolic acid (24), a product obtained by cleavage of the antibiotic streptolydigin542. 

Having thus established the main stereochemical features, the Claisen rearrangement of glycal esters could be further utilized to provide key intermediates for a number of natural product syntheses Carbohydrates served as starting materials in the total synthesis of the ionophore antibiotics lasalocid A 43 by Ireland et al. [15] and indanomycin 46 by Ley et al. [16] (Scheme 8), as well as the 3-acyl tetramic acid antibiotics tirandamycic acid 49 [17] and (+)-streptolic acid 52 [18] (Ireland et al.. Scheme 9). Several further examples have been reported in the literature [19-21]. 

Scheme 12. Ratio of reaction rates for mono- and di-Claisen rearrangements of glycal bis(ke-tene acetals) [22]...

Robin Perrier, the discoverer of the allyhc rearrangement of glycals (generally known in organic chemistry as the Perrier I reaction) as well as of the transformation of hex-5-enopyranosides to highly functionalised cyclohexanones (coined Perrier 11 reaction) has provided accounts on these milestones of carbohydrate chemistry. A chapter on base-catalysed transformations of aldo-nolactones has been provided by I. Lundt, the leading expert in this area, in collaboration with R. Madsen and an account on Claisen rearrangement reactions in carbohydrate chemistry has been contributed by B. Werschkun and J. Thiem. 

The rearrangement of glycal derivatives to l-substituted 2-enose derivatives has been applied to the preparation of i) 2,3-dideoxy-i-thiohex-2-enopyranosides (9, trimethylsilylated thiols and boron trifluoride details of the complexities of the reaction are reported) ii) 2,3-dideoxyhex-2-enopyranosyl fluorides [10, pyridine poly(hydrogen fluoride)iii) 2, 3 -unsaturated nucleosides (11, purine or pyrimidine derivatives with trityl perchlorate) (Scheme 7). 

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... 

Scheme 1 Ferrier rearrangement of glycals (1) leading to unsaturated glycosides, 3.

Vankar and coworkers have introduced AUCI3 in combination with phenylacefylene (AuCla/PhCCH) as an interesting new catalyst-system for the Ferrier rearrangement of glycals and 2-acetoxymethylglycals,... 

FIGURE 15.4 Proposed mechanism for palladium(II)-catalyzed rearrangement of glycal trichloro acetimidates. 

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

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