Fluoride donor

In the Koenigs-Knorr method and in the Helferich or Zemplen modifications thereof, a glycosyl halide (bromide or chloride iodides can be produced in situ by the addition of tetraalkylammonium iodide) is allowed to react with a hydrox-ylic compound in the presence of a heavy-metal promoter such as silver oxide, carbonate, perchlorate, or mercuric bromide and/or oxide,19-21 or by silver triflu-oromethanesulfonate22 (AgOTf). Related to this is the use of glycosyl fluoride donors,23 which normally are prepared from thioglycosides.24... 

Synthesis of Glycosyl Fluoride Donors 2.1.2.1 Fluorinating Reagents... 

BF3-OEt2 Unnatural P-sialoside derivatives are produced preferentially by using O-acetylated glycosyl fluoride donor and BF3-OEt2 as the promoter. When P-sialyl fluoride derivative 28 was reacted with acceptor 22 in the presence of BF3-OEt2 in dichloromethane, the P-sialoside 28 was obtained in a mixture of anomers (a/p 17/83) (Scheme 2.11) [44],... 

A double mutant (acid/base and nucleophile) Abg E71A E358G was developed58 which efficiently catalyzes thioglycoside formation from a glycosyl fluoridine donor (69) with inverted anomeric stereochemistry. This represents a significant improvement, as glycosyl fluoride donors are much more accessible (Fig. 29). 

Consequently, the relative contribution of xenodeborylation to fluorine addition across the C=C double bond and the ratio of the [BF4] to [XCF=CFBF3] anions depends on the electron-withdrawing character of X (acidity of the borane) and the actual ratio of XeF2 (fluoride donor) to XCF=CFBF2 (fluoride acceptor). 

J. Saha and M. W. Peczuh, Expanding the scope of aminosugars synthesis of 2-amino septanosyl glycoconjugates using septanosyl fluoride donors, Chem. Eur. J., 17 (2011) 7357-7365. 

Considering bromine trifluoride as an example, the self-ionization is shown in equation (1). Dissolution of fluoride acceptors, such as antimony pentafluoride, gives compounds formally containing the difluorobromine(III) cation, and correspondingly, dissolution of fluoride donors, such as potassium fluoride, gives compounds containing the tetrafluorobromate(III) anion. 

The octafluoroiodate(VII) ion has been reported52 to result from the interaction of the heptafluoride with the fluoride donors CsF or NOF, but its structure has not been determined. 

Lithiated fluorosilanes such as 801 and 802 may be considered as fluoride donor adducts to silanimines and behave as the free silanimines (e.g. 803) in cycloaddition reactions with C=0 compounds. The stability of the four-membered cycloadducts obviously depends on the substituents (equation 274)355. 

Ley and coworkers reported the one-pot synthesis of tetrasaccharide 176 by combining selective activation with reactivity-based armed-disarmed glycosylation [113]. As shown in Scheme 6.35, the first chemoselective coupling was achieved via selective activation of the fluoride donor 173 over the selenoglycoside acceptor 174. The resulting disaccharide intermediate was more armed than the bifunctional... 

In accordance with the solvent-system concept fluoride donors like NaF act as bases in this medium (giving Na+ and BrF-4), and fluoride acceptors such as SbF5 act as acids (giving BrF+2 and SbF-4). 

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