Preparation with Olah reagent

Glycosylfluorides. The anomeric hydroxyl or acetoxy group of monosaccharides is converted into a fluoro group by reaction with Olah s reagent in 70-90% yield. This reaction is useful for preparation of the thermodynamically more stable P-glycosyl fluoride (p/a >95 5). 

Chromanone and benzaldehyde heated a few min. with a reagent prepared by slow addition of an equivalent amount of acetic anhydride to well-cooled 65%-HCIO4 > 3-benzylidene-4-chromanone, Y ca. 100%. F. e., such as formation of benzopyrylium salts, s. J. Andrieux et al., C. r. 271 (C), 90 (1970) protonated organic compds., review, s. G. Olah, A. M. White, and D. H. O Brien, Chem. Rev. 70, 561 (1970). 

Olah prepared the elusive formic anhydride in a reaction of formyl fluoride with sodium formate at -78°C and he extended the preparation of this reagent by three condensation reactions (Eq 1.7). 

Olah and Li2 have prepared a solid form of this reagent by reaction of anhydrous HF with cross-linked poly-4-vinylpyridine. It is comparable to pyridinium poly (hydrogen fluoride) for hydrofluorination of alkenes and alkynes and fluorination of alcohols, but is easier to handle. Work-up of reactions requires only a simple filtration, and the spent reagent can be regenerated with HF for further use. 

Hexafluorosumanene 123 was prepared from sumanenetrione 120 via cyclic dithiane 122 (Scheme 40) [140]. Reaction of 122 with pyridine hydrofluoride (Olah s reagent) in the presence of iV-iodosuccinimide gave 123 in 24% yield. The strong electron-withdrawing properties of fluorine substiments cause the first reduction potential of 123 to be shifted to —1.79 V from —3.21 V (vs ferronce) of the parent sumanenes (2). 

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