Olah s reagent

There is continuous interest in cleavage of epoxides as a general method lor the preparation of fluorohydrins Epoxides are effectively cleaved under mild conditions by a 70% hydrogen fluoride-pyridine complex (Olah s reagent). The... 

Reactions of benzylic a,P-aminoalcohols and a-hydroxyazindines with Olah s reagent provide a highly efficient way to a P-fluoroamines, a-fluoro-azindines, and ot,Y-difluoroamines [dS] (equations 43 and 44)... 

Fluorodediazoniation of 2-fluoro-2-phenylethylamines with sodium nitrite m Olah s reagent (70% anhydrous hydrogen fluoride-30% pyridine) gives high yields of 1,1-difluoro-2-phenylethanes arising from 1,2 migration of phenyl fJ] (equation 2)... 

High-yield deaminative fluorination of a-atmnocarboxylic acids to a-fluoro-carboxylic acids can be effected with sodium nitrite in Olah s reagent [5, 6] (equation 3 and Table 2)... 

Fluoromethylketones are obtained by dediazoniative hydrofluorination with anhydrous hydrogen fluoride [91, 92 93] or Olah s reagent [d] (equation 23)... 

Oxazolidinones have also been used as intermediates in simple transformations utilising their peculiar reactivity. The absolute configuration of WBoc-P-aminoalcohol 213 can be easily inverted via Sn2 cyclisation to oxazolidinone 214 <00TL10071>. Treatment with Olah s reagent (HF-Pyridine) of 4-alkyl-5,5-diphenyl-oxazolidinones 216 afforded the corresponding a-(fluorodiphenylmethyl)alkylamines 217 <00TA2033>. 

Nevertheless, a different selectivity has really been observed83 in bromofluorination reactions of 1,5-cycloalkadienes with NBS/Et3N-3HF or Olah s reagent. The reaction of 1,5-cyclooctadiene (3) with the former reagent yields mainly the 1,2-addition product 52, but when the reaction is carried out with Olah s reagent only compounds 53 and 54, arising from the usual transannular jr-cyclization, are formed (equation 53). 

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 two most widely accepted hydrogen fluoride systems, besides pure hydrogen fluoride, are 70% hydrogen fluoride/pyridine (Olah s reagent)10 11-31-33 and tricthylaminetris(hydrogen fluoride).9 32 33-316 Tetrahydrofuran. various other amines, amides, carbamic acids and esters. 

Branched alkenes and cycloalkenes react more readily. The hydrofluorinations may be carried out advantageously with 70 % hydrogen fluoride/pyridine (Olah s reagent) using tetrahydro-furan as a solvent,10,31 but a homogeneous system forms in this case. Therefore, the workup procedure was carried out by quenching the reaction mixture with ice water and neutralization with sodium hydrogen carbonate hydrofluorinations of various alkenes in this way are described in ref 40. 

It is noticeable that neither the most commonly used less acidic triethylamine tris(hydrogen fluoride) nor the more acidic Olah s reagent (70% HF/pyridine) lead to the generation of a cyclic fluoro alcohol from 2,6-dimethylhept-5-enal (7).395... 

The combination of A/-halosuccinimides with polyfluorinated ammonium salts, in particular A/-halosuccinimide-triethylamine trisfhydrogen fluoride)42 (Method C), is convenient and effective for the halofluorination of alkenes. These easy-to-handle reagents allow work to be carried out at room temperature in conventional glass apparatus, while Olah s reagent requires polyethylene equipment. The reaction of various alkenes with A -halosuccinimide-triethylamine trisfhydrogen fluoride) in dichloromethane or diethyl ether at 0 C is complete within 3-5 hours giving the halogen fluoride addition products in 70-95% yield. 

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