Glycosylation boron trifluoride

Glycosylation of 3-amino-5(7)//-[l,2,4]triazolo[4,3-3] l,2,4 triazole 17 with 1-O-acetyl- 2,3,5-tri-O-benzoyl-D-ribo-furanose 18 or 2,3,5-tri-O-benzoyl-D-ribofuranosyl bromide 19 can be selective or nonselective, depending on the reaction conditions (Scheme 1). In the presence of trimethylsilyl triflate or boron trifluoride etherate, the... 

Takahashi and coworkers described the one-pot synthesis of core 2 branched oligosaccharides [236], It was found that boron trifluoride complexed with a tri-methylsilyl ether would enhance the nucleophilidty of the silyl ether. As a result, glycosylations of the 6-O-TMS modified acceptor with a glycosyl fluoride provided... 

When neighboring-group participation is a feature of the glycosylation reaction, the use of a base in this manner frequently results in the isolation of orthoesters rather than the desired glycosides. In the case of activation by triflic anhydride, it is possible to avoid this problem by simply omitting the base. Alternatively, with more sensitive substrates, the hindered base may be retained and boron trifluoride ethe-rate be added to promote the rearrangement of the orthoester to the glycoside, as in... 

Despite these restrictions, the acceptor-bound succinoyl MPEG28 was found to permit glycosylations with glycosyl trichloroacetimidates promoted by boron trifluoride, triflic anhydride, and trimethylsilyl or triethylsilyl triflates, with glycosyl halogenates promoted by silver triflate, and with thioglycosides promoted by the iodonium ion. It is compatible with long-term ester protection, with allylic,... 

Enantiomerically pure glycosyl stannanes gave, after tin-lithium exchange and reaction with oxiranes in the presence of boron trifluoride diethyl ether complex, alkylation products as diastereomers (1 1 -2 1 d.r.) with complete retention at the stereogenic center a to the oxygen atom41. 

H. Kunz and W. Sager, Stereoselective glycosylation of alcohols and silyl ethers using glucosyl-fluorides and boron trifluoride etherate, Helv. Chim. Acta 68 283 (1985). 

Glycosides of unprotected D-glycuronic acids have been formed directly in the appropriate alcohol with boron trifluoride etherate as catalyst, affording D-glycosiduronates.246 D-Glucosyluronic acid trichloroacetimidate has also been used for glycosylation of uronic acids.247... 

The chiral piperidinones 46 formed by the reaction between Danishefsky s diene and the glycosyl imines are valuable synthons for the synthesis of higher substituted piperidine derivatives. 2,6-Disubstituted piperidinones 49 are obtained by addition of organocuprates complexes with boron trifluoride [53]. The reaction pathway is illustrated in Scheme 30. 

Anastasia, M, Allevi, P, Ciuffreda, P, Fiecchi, A, Scala, A, A simple and ready internal C-glycosylation of 2,3,5-tri-O-benzylglycofuranoses promoted by the boron trifluoride -diethyl ether complex, Carbohydr. Res., 208, 264-266, 1990. 

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