Pyridinium poly-

Alkyl and aryl isocyanates react with anhydrous hydrogen fluonde to give carbamyl fluorides [J, 55], the more conveniently handled pyridinium poly(hydro-gen fluoride) reagent can also be used, although the yields tend to be poorer [9] (equation 10). 

Oiazo ketones and esters react with A -halosuccinimides in pyridinium poly(hydrogen fluoride) to give geminal halofluoro denvatives [9] (equation 21)... 

Dediazoniation of three o-substituted benzenediazonium salts in pyridinium poly(hydrogen fluoride) yields different products depending on the substituent, as Olah and Welch (1975) have found. The 2-methyl derivative gives 2-fluoro-toluene. With the 2-nitrobenzenediazonium ion the main product is 3-nitrofluoro-benzene, the 2-isomer being formed only in small quantities. Finally, the 2-tri-fluoromethyl derivative yields all three isomeric trifluoromethylfluorobenzenes. 

Variations in the proportions of the different components of product mixtures are observed in reactions that involve anhydrous HF31-80-82-84-85 and in pyridinium poly(hydrogen fluoride).86 These variations can also be explained in terms of kinetic and thermodynamic control. Thus, less stable, but more rapidly formed, dianhydrides isomerize under thermodynamic conditions to give more-stable products. It has also been noted that the starting isomeric forms of the ketose influence the kinetic outcome of the reaction.119... 

It might be pertinent to consider the basis of the extremely facile isomerization in anhydrous HF or pyridinium poly(hydrogen fluoride). HF is an extremely strong proton donor, but it is also a potent fluorinating agent. It is highly probable that the postulated cationic intermediates in these isomerizations are fluori-nated and serve as reactive intermediates in the same way as the fructofuranosyl... 

In 1993, the di-D-fructose dianhydrides were summarized as being of little, if any, commercial importance. 73 However, a search of the literature reveals an appreciable number of patents issued since 1989 for the manufacture of these compounds. These include enzymic methods for the production of individual dianhydrides (Ref. 130) or methods of production of mixtures using anhydrous HF or pyridinium poly(hydrogen fluoride) (see Ref. 131). Most cite the di-D-fructose dianhydrides as low-calorie sweetening agents (Ref. 132), and some claim anti-cariogenic properties (Refs. 132 and 133). 

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. 

The action of pyridinium poly(hydrogen fluoride) on compounds 29— resembles that of anhydrous hydrogen fluoride on peracetylated -glucopyranose (2, ), and of silver tetrafluoroborate in diethyl ether (when prolonged) on... 

However, the ring expansion of 1-substituted tertiary cyclopropanemethanols to tertiary fluo-rocyclobutanes is efficiently brought about with pyridinium poly(hydrogenfluoride) in the presence of diisopropylamine and potassium fluoride-hydrogen fluoride.19 2(1 Under the strictly anhydrous conditions employed, the intermediate cyclobutyl cation is efficiently trapped. Illustrative is the rearrangement of methanesulfonate 9, the key step in a synthesis of ( )-2-fluorograndisol.21 Other examples are collected in Table 3. 

Hydrogen Fluoride/Pyridine [Pyridinium Poly(hydrogen fluoride)], (70% Hydrogen Fluoride by Weight) 31... 

By using the same reagent combination of nitrosonium tetrafluoroborate and pyridinium poly(hydrogen fluoride) (PPHF), diarylacetylenes could be converted into diaryltetrafluoro-ethanes in moderate to good yields (Table 19).87... 

Adamantane and other tertiary hydrocarbons have been converted by applying this method [nitrosonium tetrafluoroborate/pyridinium poly(hydrogen fluoride) (PPHF)] into the corresponding fluorohydrocarbons in excellent yields.88... 

The reaction of 1,4,9-tribromodiamantane (2) with N02 BF4, /pyridinium poly(hydrogen fluoride) (PPHF) shows the unexpected formation of 1,4,7,9-tetrafluorodiamantane (3).91... 

Cycloalkyl and secondary alkyl bromides react with N02 BF4 in pyridinium poly(hydrogen fluoride) solution to yield /J-fluorinated compounds in moderate to good yields. In the case of the cyclic starting materials like 1-bromocyclohexane only trans-substituted products are formed (see Table 22). 

Fluoronitroalkanes can be conveniently prepared by adding an alkene to a solution of nitronium tetrafluoroborate dissolved in pyridinium poly(hydrogen fluoride).94 For example cyclohexene (6) gives 1 -fluoro-2-nitrocyclohexanes (7) in good yields.94... 

One-step electrophilic hydroxylation of aromatic compounds using various peroxide reagents in the presence of acid catalysts has been achieved. The systems studied include hydrogen peroxide in the presence of sulfuric acid,766 hydrogen fluoride,767 Lewis acids,768 769 and pyridinium poly(hydrogen fluoride).770 Lewis acid-promoted electrophilic hydroxylation with peracids,771,772 di-tcrt-butyl peroxide,773 and diisopropyl peroxydicarbonate774 775 were also described. A common feature of these reagents is the formation of monohydroxylated compounds in low yields. 

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