Selectfluor reagents:

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. 

Sankar Lai G, Pastore W, Pesaresi R (1995) A convenient synthesis of 5-fluoropyrimidines using 1 -(chloromethyl)-4-fluoro-1,4-diazabicyclo[2.cntdot.2.cntdot.2]octanehis(tetrafluoroborate)-selectfluor reagent. J Org Chem 60 7340-7342... 

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]. 

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). ... 

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... 

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... 

A proposed reaction mechanism for the formation of fluorinated l,3-dihydro-2/7-indol-2-ones is shown in Scheme 72 <20000L639>. Reaction of 3-substituted indole with Selectfluor 310 gave 3-fluoro-37/-indole 312 as an unstable intermediate that underwent loss of HF due to addition of water. A subsequent [l,5]-prototropic shift gave the indol-2-ol 313. Fluorination of intermediate 313 with additional reagent resulted in indol-2-one 311 as the final product. Formation of nonfiuorinated indol-2-one 314 as a minor side product was explained by the tautomerism... 

Electrophilic fluorinating reagents such as Selectfluor and related compounds can be used for the ring fluorination of phenols. The reaction of phenol with l,3-bis(4-fluoro-l,4-diazoniabicyclo[2.2.2]oct-l-yl)propane tetratriflate in methanol gives moderate yields... 

Selectfluor, CH3CN, 5% H2O, 5h, rt, 87-92% yield. This reagent also cleaves dithianes and THP ethers. ... 

Selectfluor , CH3CN or CH3NO2, 5% H2O, <5 min, 80-95% yield. The THP and p-methoxybenzylidene groups are also cleaved in excellent yield with this reagent. 

A major drawback so far for all NF-reagents is their relatively high molecular weight and their low content of active fluorine. For example, for Selectfluor the ratio of active fluorine to the molecular weight is only 5.4%, for NFTh it is 8.0%, and for NFPy 6.0%. This issue was addressed by synthesis of more compact fluorination reagents [191]. One approach towards this goal was to link two or more pyridinium units to a single molecule (4, commercialized as Synfluor). 

Newer approaches make use of derivatives of quinuclidinc alkaloids, such as quinine. The quinine derivative is first converted into the fluorination reagent by Selectfluor, in one-pot procedure, and in a second step reacted with the desired substrate (Scheme 2.93). The enantiomeric excesses achieved with this type of reagent are higher than for the N-fluoroimides but still below those of other enantioselec-tive reactions. 

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 electrophilic fluoridation reagent Selectfluor [152, l-chloromethyl-4-flu-oro-l,4-diazabicyclo[2.2.2]octane bis(tetrafluoroborate)] was allowed to react with tii-O-acetyl-D-galactal, and the resulting salt 153 l-(3,4,6-tri-0-acetyl-2-deoxy-2-fluoro-a-D-galactopyranosyl)-4-chloromethyl-l,4-diazabicyclo[2.2.2]octane bis(tet-rafluoroborate) reacted with NaNs alTording the 1,2-trans fluoro azide 154. ... 

Shreeve and coworkers reported a convenient procedure for preparing (difluoroiodo)arenes by direct fluorination of the respective iodoarenes with the commercially available fluorinating reagent Selectfluor in acetonitrile solution. This procedure has been further improved by using the corresponding arene, elemental iodine and Selectfluor in a one-pot oxidative iodination/fluorination procedure [33]. 

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