C-Glycosyl derivative

C-Glycosyl derivatives may be prepared by utilizing glycosyl fluorides. Ishido and coworkers reported that the reaction of 2,3,5-tri-O-benzyl-a-(36a) or - -D-ribofuranosyl fluoride (36fi) with isopropenyl trimethylsilyl ether under BF3 catalysis (0.1 -0.05 mol. equiv. for the fluoride, in ether or acetonitrile) gave a mixture of 4,7-anhydro-5,6,8-tri-C)-benzyl-l,3-dideoxy-D-altro- (139, major) and -D-a//o-2-octulose (140) 139 was stated to isomerized to 140 (should be vice versa) under Lewis acid catalysis. Similar... 

It is clear that the successful application of these C-glycosylations to the D-aldofuranose series, by treatment of the appropriate per-O-acylaldofuranosyl halides with organometallic reagents, could lead to synthetically useful C-glycosyl derivatives. Zhdanov and co-... 

Fig. 40 Synthesis of a-C-glycosyl derivative of nojirimycin and its analogues. Reagents and conditions (a) BnNH2, PTSA (b) CH2=CHCH2MgBr, Et20 (c) FmocCl, Na2C03 (d) PCC (e) piperidine, DMF (f) NaHB(OAc)3, AcOH, Na2S04, 1,2-dichloroethane, -35 °C.

Methods based on p-elimination from C-glycosyl derivatives. 

The glycosyl halide (1.5 mmol), p-dicarbonyl compound (2 mmol), anhydrous K3P04 (0.S5 g) and TBA-Br (24 mg, 0.075 mmol) in McCN (10 ml) are stirred at room temperature. When the reaction is complete, as indicated by TLC analysis, the mixture is filtered and evaporated to yield the C-glycosyl derivative. 

Scheme 18 Claisen condensation of aldono-1,5-lactones leading to exocyclic epoxides and further conversion into C-glycosyl derivatives...

Scheme 19 C-Glycosyl derivatives by addition of allylmagnesium chloride to aldonolactones...

J. C. Lopez and B. Fraser-Reid, Serial radical reactions of enol ethers Ready routes to highly functionalized C-glycosyl derivatives, J. Am. Chem. Soc. 111 5450 (1989). 

Some of the most useful 2,3-unsaturated C-glycosyl derivatives are the allyl compounds such as 92, made by use of allyltrimethylsilane, and a notable feature of this compound is that it can be produced directly from tri-O-acetyl-D-glucal with DDQ as promoter.111 A further surprising feature of this C-allylation procedure, however, is its applicability to glycals that are not O-substituted. Reactions are carried out in dichloromethane-acetonitrile at low temperatures with trimethylsilyl triflate as catalyst, and almost quantitative yields of 2,3-unsaturated C-allyl glycosyl compounds are recorded, with the a anomers being formed almost exclusively.112... 

Intramolecular radical cyclization followed by trapping of the intermediate with an enone has been investigated by Fraser-Reid and co-workers [95JOC3871] as a method for the synthesis of highly functionalized C-glycosyl derivatives. The control of the anomeric stereochemistry as well as the facial selectivity in the addition to the chiral enone is impressive. 

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