Glycosyl enamines

Although the transformation of glycosylamines (such as 15) into fully unprotected glycosyl isothiocyanates by reaction with thiophosgene was already reported in the 1970s,58 61 these compounds were later shown to be unstable,62 and no further chemistry has been reported. Hie synthesis of stable, fully protected hexopyranosyl isothiocyanates by the thiophosgene reaction was first reported by Fuentes Mota and coworkers.63 65 Hie reaction sequence involves a glycosyl enamine (for example, 16) as key intermediate which., after O-prolection (->17), is hydrolyzed under mild condi-... 

Keywords Glycosjd azides - Glycosjdamines Glycosyl enamines - Glycosyl heterocycles Triazoles Click chemistry... 

Suitably protected glycosyl halides or acetates, upon Lewis-acid promoted SN1 heterolysis, generate glycosyl cation intermediates that can react with electron-rich arenes, heteroarenes, Me3SiCN, enoxysilanes, enamines, allyl silanes and stannanes, acetylenyl silanes and stannanes affording C-glycosyl compounds. 

In a search for cytostatic quinones, both benzoquinones and naphthoquinones have been treated with glycosyl azides labile N-glycosyl triazolines are formed, which aromatize to triazoles or lose nitrogen to give enamines.317... 

Kunz, H, Muller, B, Weissmuller, J, Stereoselective synthesis of C-glycosyl compounds via Michael addition of trimethylsilyl enol ethers and enamines to hex-l-enopyran-3-uloses, Carbohydr. Res., 171, 25-34, 1987. 

Scheme 2.53 Examples of the fluorination of alcohols with a,a-clifluoroalkylamines or a-fluroro-enamines. Synthesis of cycloalkyl fluorides, fluorosteroids, fluoroterpenes, and glycosyl fluorides with G-fluoroenamines [122, 123].

The approach to nucleoside synthesis developed by Ogura et al. (Heterocycles, 911, 8, 125, and earlier references), which involved the reaction of glycosyl isothiocyanates with substituted hydrazines to give thiosemicarbazides which were cyclized with NBS, and finally desulphurized to give the required heterocycle, has now been applied to the synthesis of pyrazolopyrimidine nucleosides derived from D-glucopyranosyl, D-arabinopyranosyl, and d-ribofuranosyl isothiocyanates. Syntheses of nucleoside analogues from reactions of glycosyl isothiocyanates with amino-acids, enamines, and diamines have been summarized. ... 

The IV-linked disaccharide (S) was obtained in 38% yield during an attempted O-glycosylation (with tetra-O-benzoyl-ot-D-glucopyranoyl bromide -AgOTf-colIidine)/ The N-glucosyl-enamines (6) were prepared by reaction of D-glucosylamine with the sodium salts of malondialdehyde or its a-methyl analogue. Several 2A -disubstituted 5-chloro-4-(iJ-D-... 

Otherwise aminomethyl -glycoside derivatives may be obtained by reduction of glycosyl cyanides (Chapters 21, 22)." Condensation of enamines of j9-ketoesters and ketones with tetra-Q-benzyl-a-D-glucopyranosyl chloride activated with silver triflate gave a-C-glucosides as epimeric mixtures in 80-85% yield (Scheme 15). ... 

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