Glycosyl carbene

The preparation of glycosyl tosylhydrazones and their reaction (via a glycosyl carbene) with acrylonitrile to afford all stereoisomers of the glycosyl cyanocyclopropane products has been reported. Similar work has been reported by other workers (See Vol. 25, Chapter 14, Scheme 29). 

Synthesis of amino-sugar glycosides is covered in Chapter 3, the formation of 2-acetamido-2-deoxy-D-glucosides from diazirines via glycosyl carbenes in Chapter 10, and the conversion of a deoxynojirimycin derivative into 2,6-dideoxy-2,6-imino-L-gulonic acid in Chapter 18. 

Mangholz, S.E. and Vasella, A., Glycosyl carbenes. Part 5. Synthesis of glycono-1,5-lactone tosyl-hydrazones as precursors of glycosylidene carbenes, Helv. Chim. Acta, 74, 2100, 1991. 

Several other studies concerning tetrazole-containing compounds were leptorted. The 1-bromo-glycosyl cyanide 15 was converted to the tetrazole derivative 16 in 72% yield by treatment with 2 eq LiNs/DMF/S d <96T9121>. Shorter reaction times led to formation of the 1-azido-pyranosyl cyanide. (Hydroxyphenyl) carbenes could be formed by thermal decomposition of the appropriate 5-substituted tetrazoles 17 <96JOC4462>. 

Vasella et al. introduced an approach to glycoside synthesis using the glycosylidene carbene generated from the diazirine sugar as a novel type of glycosyl donor. The... 

Carbene-mediated methylenation of aldonolactones provides a direct route to 1-methylene sugars, which may be used as intermediates for the preparation of furanoid or pyranoid C-glycosyl compounds, or chiral precursors for the synthesis of natural products. 

Fluoroalkyl Glycosides (RFn-(CH2)2-n-0-sugar) and Perfluor-oalkylidene Acetals Derived from Sugars The very low nucleophilicity of fluoroalcohols makes it difficult to substitute of a hydroxyl (anomeric or not). ° This is the reason why this type of ether is not very common. Such ethers have only been isolated in very small quantities in solvolysis reactions, or in carben insertions, performed in fluorous alcohols.Preparation of these ethers has been solved by means of the Mitsunobu reaction. This reaction is known to be dependent on the pA a of the acceptor of the glycosyl the acidity of fluorous alcohols allows a much easier deprotonation than with non fluorinated alcohols." ... 

A similar method has been used to synthesize spirocyclic glycosyl diaziridines and diazirines (e.g., 66 and 67), which are used as glycosylidene carbene precursors. The diaziridine is made by reaction of the sulfonylated oxime 65 with ammonia, followed by oxidation to the diazirine with iodine (Scheme 23). 

Toth, M., Somsak, L. exo-Glycals from glycosyl cyanides. Eirst generation of C-glycosylmethylene carbenes from 2,5- and 2,6-anhydroaldose tosyihydrazones. J. Chem. Soc., Perkin Trans. 1 2001, 942-943. 

Although not radical in nature, this class of species is electron deficient and their inclusion here is warranted. Vasella has continued his work on glycosyl car-benes. The carbene generated from 52, when trapped with dimethyl fumarate of N-phenylmaleimide, gave 53 and 54, respectively (Scheme 12) [19]. 

Asymmetric synthesis of nucleosides via molybdenum-catalyzed alkynol cycloisomerization coupled with stereoselective glycosylations of deoxyfuranose glycals and 3-amidofuranose glycals. Journal of the American Chemical Society, 118, 6648-6659 (b) McDonald, F.E. and Chatterjee, A.K. (1997) Group VI metal-promoted endo-azacyclizations via alkyne-derived metal vinylidene carbenes. Tetrahedron Letters, 38, 7687-7690 ... 

Some carbohydrate acetylenic alcohols have been converted to metal carbene spirocyclic derivatives, e.g. 22 (Scheme 4) Acetobromoglucose has been converted into tri-O-acetyl-D-glucal in 90% yield by way of a glycosyl chromium-(III) complex, and an organomercury intermediate featured in a synthesis of tri-O-benzyl-2-C-methyl-D-glucal covered in Chapter 14. 

Carba disaccharide 97 has been prepared by insertion of a sugar glycosylidene carbene (made in situ from a glycosyl diazirine derivative) into OH groups of protected deoxy m o-inositoI orthoformate derivatives. ... 

C-glycosides Vasella has reviewed his work on glycosylidene carbenes which is of relevance to the subject, and the use of glycosyl carbanions in C-glycoside synthesis has also been surveyed. ... 

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