Selectfluor F-TEDA

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). ... 

Fluorocyclohexa-2,5-dienone derivatives were obtained in high yield by reaction of para-substituted phenols with l-fluoro-4-chloromethyl-l,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) (Selectfluor F-TEDA-BF4) or its 4-hydroxy analogue (Accufluor NFTh) in acetonitrile (equation 98). Estrogen steroids were readily converted to /1-fluoro-l,4-estradien-3-one derivatives in high yields using this method (equation 99) °. 

Newer QM/MM simulations of the electrophilic fluorination of a malonate coordinated to a titanium center with a simplified Selectfluor (F-TEDA) analog [189] throw a new light on the electron transfer/fluorine transfer mechanism. During the approach of the electrophilic fluorine toward the carbon nucleophile an electron is transferred from the nucleophile to Selectfluor, then fluorine is transferred to the nucleophile. Interestingly, the transition state for transfer of the fluorine radical is formed only if a polar solvent (acetonitrile) is used. If the simulation is carried out in vacuo, the reaction stops after the initial electron transfer. 

The range of possible fluorination reactions on electron-rich double bonds, eno-lates, and enol ethers, with Selectfluor (F-TEDA-BF4) as example, is depicted in Scheme 2.88. Yields from the fluorination of unstabilized carbanions, for example phenyl magnesium bromide, are usually relatively low, mostly because of competing oxidation side-reactions. 

CljPyFlOTf [pyFlOTf F-TEDA-BF4 (Selectfluor) F-TEDA-PFg Selectfluor II... 

This reagent is known under the commercial name of Selectfluor F-TEDA-BF. ... 

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. 

Scheme 2.93 Enantioselective electrophilic fluorination of silyl enol ethers by N-fluorodihydro-quinine 4-chlorobenzoate. The enantioselective fluorination reagent is generated in situ from F-TEDA-BF4 (Selectfluor) and dihydroquinine 4-chlorobenzoate [206].

The asymmetric fluorination of 3-ketoesters has been achieved in 62-90% ee using F-TEDA (Selectfluor) as fluorine source in the presence of 0.5 mol% of the chiral nonracemic titanium-based Lewis acid (5.108). ° A greater range of p-ketoesters are fluorinated with higher ee using catalytic quantities of the palladium-BINAP complex (5.109) and N-fluorobenzenesulfonamide (NFSI). ° In both cases the reaction proceeds through the intermediacy of a chiral enolate. 

Chlorine and iodine can be introduced into aromatic rings by electrophilic sub-stimtion reactions, but fluorine is too reactive and only poor yields of mono-fluoroaromatic products are obtained by direct fluorination. Instead, other sources of "F+" are used in which a fluorine atom is bonded to a positively charged nitrogen. One of the most common such reagents goes by the acronym F-TEDA-BF4 and is sold under the name Selectfluor. 

In contrast to nucleophilic fluorination, fluoroisoquinoline syntheses via direct electrophilic fluorination were reported relatively recoitly. In 2007, Price developed direct electrophilic C-H bond fluorination of an isoquinoline derivative with Selectfluor (l-(chloromethyl)-4-fluoro-l,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate), F-TEDA), [39] which is known as an efficient electrophilic fluorine source [40-42]. 

---