Selectfluors

The transformation of 1-hydroxy sugars to the corresponding glycosyl fluorides can be achieved by a mixture of Selectfluor 3 (Figure 2.2) and methyl sulfide presumably through a fluorosulfonium ion 9, which then reacts with the anomeric... 

Methods for indirect oxidation have also been developed. The combination of KF/ wCPBA in acetonitrile and water has been used to generate KOF CH3CN reagent, a mild and selective oxidant that reacts at 0 °C with no overoxidation [78]. This reagent functions by providing a fluorosulfonium ion intermediate, which is hydrolyzed in the presence of water to the desired sulfoxides. As a result of the indirect oxidation method, the typical stereoselectivity of mCPBA-type oxidations is not observed here. The KOFCH3CN oxidant is similar in scope and mechanism to 1-fluoropyridinium triflates, Selectfluor [302] and the more classical t-butyl hypochlorite [288]. 

Several 2-fluoroerythromycin derivatives have also been prepared by means of electrophilic fluorination with Selectfluor of the enolate of the )S-ketoester fragment (Fig. 45) [121]. Fluorination is stereoselective and leads to the a-fluo-rine compound [122]. Two derivatives of 2-fluoroerythromycin are in clinical development HMR-3562 and HMR-3787). These compounds are promising agents for the treatment of respiratory pathogens resistant to erythromycin A (Fig. 45) [123]. 

G.S. Lai, Site-selective fluorination of organic compounds using 1-alkyl-4-fluoro-1, 4-diazabicyclo[2.2.2]octane salts (selectfluor reagents), J. Org. Chem. 58 (1993) 2791-2796. 

The asymmetric fluorination of enolates by means of chiral metal complexes has been reported with Selectfluor in the presence of a chiral Lewis acid derived from TADDOL (TiCl2/TADDOL), or with F-A-sulfonimide (NFSI) with palladium complexes and chiral phosphines. 

In the presence of several equivalents of N-F-type reagents, " it is possible to perform the difluorination of enolates of ketones, amides, and enamines. The difluorination of nucleosides has also been performed with Selectfluor (Figure 2.11). ... 

Amphotericin B (AmB) is a polyenic macrolide used in fungal infections and leishmaniasis, despite severe side effects (Figure 4.60). Fluorination of the macrolide skeleton has been performed using Selectfluor for F NMR studies on the mechanism of ion-channel formation in membranes by amphotericin B. ... 

Numerous methods to prepare glycosyl fluorides can involve nucleophilic fluori-nation reagents (e.g., HF, DAST) or electrophilic reagents (e.g., Selectfluor ) (cf. Chapter 2) The synthesis and reactivity of glycosyl fluorides have been... 

Fluoronucleosides that have an exocyclic double bond can be prepared from a fluorosulfoxide. This latter compound is obtained by electrophilic fluorination of the corresponding sulfide with Selectfluor (F-TEDA-BF4) (Figure 6.12). ... 

The new family of l-alkyl-4-fluoro-l,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) salts (5a, 5b, 6, 7) (commercial F-Teda BF4, 6), which are selective and easy-to-handle fluorinating reagents76,80 87 90 are commercially available under the trade name Selectfluor. 

Alkanes. Earlier observations had demonstrated the possibility of fluorination at tertiary C—H sites (see Section 10.1.1). New studies have shown that electrophilic fluorination at both secondary and tertiary carbon atoms may be carried out by elemental fluorine or Selectfluor l-(chloromethyl)-4-fluoro-l,4-diazabicyclo[2.2.2] octane bis(tetrafluoroborate) in acetonitrile 249... 

F2 in N2, MeCN, 0 °C 63% yield, 53% conversion Selectfluor, MeCN, reflux 22% yield, 100% conversion... 

Partially proton-exchanged Na faujasite X, in turn, is the best catalyst for selective monochlorination with tert-butyl hypochlorite.258 NaX, NaY, and NaKL zeolites used in the chlorination of toluene with sulfuryl chloride undergo rapid deactivation because of the accumulation of polychlorinated toluenes in the pores of the catalysts and dealumination.259, 260 Direct electrophilic fluorination of aromatics can be effected by using Selectfluor in the presence of triflic acid.261 Electrophilic fluorination may also be carried out by R2NF and R3N+FA reagents.262 Elemental fluorine may also act as a powerful electrophile in acidic media (sulfuric acid, trifluoroacetic acid, or formic acid), but monosubstituted aromatics give isomeric mixtures.263-265... 

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