Pyridinium poly hydrogen fluoride - Olahs reagent

1 Pyridinium poly(hydrogen fluoride) - Olah s reagent 

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The action of pyridinium poly(hydrogen fluoride) (Olah s reagent) on a-hydroxy aziridines is influenced by the reaction conditions, as well as the nature of the starting aziridine (Table 13). ... 

Tabic 13. Action of Pyridinium Poly(hydrogen fluoride) (Olah s Reagent) on a-Hydroxy Aziridines ... 

Fluorohydrins.1 Both this reagent (1) and Olah s pyridinium poly (hydrogen fluoride) (2) serve as an attenuated source of hydrogen fluoride, and both convert simple epoxides into fluorohydrins, but reactions with 1 require higher temperatures than those with 2. The two reagents can differ in the regioselectivity, with steric factors being more important in reactions of 1 than those of 2. 

In the case of 2,3,5-tri-O-benzoyl-D-ribofuranose (27) pyridinium poly(hydrogen fluoride) was added to a solution of in anhydrous dichloromethane and the solution was shaken at room temperature for 10 h in an atmosphere of dry argon. Anhydrous acetone was found to be equally effective in most reactions. The reaction of compound with Olah s reagent required the use of c.nhydrous acetone or anhydrous dichloromethane—collidine [1 1 (v/v)] in the case of compound 30 the addition of collidine was disadvantageous, whereas in the case of compound best results were obtained using anhydrous acetone—collidine [1 1 (v/v)] as the solvent. Compounds 32 and 33 were treated using pyridinium poly(hydrogen fluoride) as the only solvent. Reaction times varied from 2 h for compound 31 to more than 12 h for 32 and 33. 

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. 

The hydrogen fluoride/pyridinc [pyridinium poly(hydrogen fluoride)] reagent, which is commercially available, was introduced as a fluorinating reagent for secondary and tertiary alcohols by Olah in 1973. However, the reagent was used as early as 1960 by Bergstrom for the synthesis of fluoro steroids. 

Olah GA, Welch IT, Vankar YD et al (1979) Synthetic methods and reactions. 63. Pyridinium poly (hydrogen fluoride) (30% pyridine-70% hydrogen fluoride) a convenient reagent for organic fluorination reactions. J Org Chem 44 3872-3881... 

The reaction of 2//-azirines (e.g.. 1) with hydrogen fluoride in pyridine [pyridinium poly(hy-drogen fluoride). Olah s reagent]23,24 gives /1,/Tdifluoro amines (e.g., 7) or a-fluoro ketones (e.g., 5) (Table 10). In some cases, pyrazines (e.g.. 9) are the main reaction products (Table 10).31 3 5 2//-Azirines are more reactive than aziridines towards pyridinium poly(hydrogen fluoride) (sec Section 1.1.8.7.). 

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