Stereoselective intramolecular glycosylation

Scheme 10-84 Remote tethers are less useful for stereoselective intramolecular glycosylation.

One aspect, besides the size of the ring that forms upon intramolecular glycosylation, governing the stereoselective outcome using this concept has been shown to be... 

Seward, CMP, Cumpstey, I, Aloui, M, Ennis, S C, Redgrave, A J, Fairbanks, A J, Stereoselective cis glycosylation of 2-0-allyl protected glycosyl donors by intramolecular aglycon delivery (lAD), Chem. Commun., 1409-1410, 2000. 

Carbohydrates with a hydrazono ester at the C-2 position underwent intramolecular radical C-glycosylation upon reaction with tin hydride and AIBN, to afford the corresponding lactone in good yield (O Scheme 47). Although the stereoselectivities of the amino acid moiety were generally low, the methods have been used for the synthesis of a variety of C-glycosyl amino acids [73], The following reaction was a key step in the total synthesis of furanomycin, an antibiotic. 

Scheme 10-93 Leaving group-based intramolecular glycoside bond formation is an attractive route to stereoselective glycosylation.

A new method for the stereocontrolled synthesis of pyrimidine p-D-2 -deoxy-ribonucleosides involves the use of a photolabile directing group at C-2, and is illustrated by the case in Scheme 2. New glycosyl donors that have been employed with good to excellent stereoselectivity in reactions with silylated pyrimidines are the deoxyribofuranosyl phosphoramidate 36 and the thiocarba-mate 37 in this latter case, intramolecular participation by the sulfur is thought to be involved in ensuring P-selectivity. ... 

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