Polyhydrogen fluoride Pyridine

HF) /Pyr, 25°, 60 min, 100% yield. Polyhydrogen fluoride/pyridine cleaves most of the protective groups used in peptide synthesis. 

Primary, secondary, and tertiary alcohols can be converted to any of the four halides by treatment with the appropriate NaX, KX, or NH4X in polyhydrogen fluoride-pyridine solution." This method is even successful for neopentyl halides. Another reagent that converts neopentyl alcohol to neopentyl chloride, in 95% yield, is PPh3-CCl3CN." ... 

The reaction can be applied to simple epoxides if polyhydrogen fluoride-pyridine is the reagent. The epoxide-to-fluorohydrin conversion has also been carried out with Sip4 and a tertiary amine.Chloro-, bromo-, and iodohydrins can also be... 

When diazo ketones are treated with HBr or HCl, they give the respective a-halo ketones, but HI does not give the reaction, since it reduces the product to a methyl ketone (10-87). a-Fluoro ketones can be prepared by addition of the diazo ketone to polyhydrogen fluoride-pyridine. This method is also successful for diazoalkanes. 

These reactions are most important for the preparation of acyl fluorides. " Acyl chlorides and anhydrides can be converted to acyl fluorides by treatment with polyhydrogen fluoride-pyridine solution" or with liquid HF at — 10°C. Formyl fluoride, which is a stable compound, was prepared by the latter procedure from the mixed anhydride of formic and acetic acids. Acyl fluorides can also be obtained by reaction of acyl chlorides with KF in acetic acid or with DAST. Carboxylic esters and anhydrides can be converted to acyl halides other than fluorides by the inorganic acid halides mentioned in 10-77, as well as with PhsPXa (X = Cl or but this is seldom done. Halide exchange can be carried out in a... 

Any of the four hydrogen halides can be added to double bonds.The compounds HI, HBr, and HF add at room temperature. The addition of HCl is more difficult and usually requires heat, although HCl adds easily in the presence of silica gel. The reaction has been carried out with a large variety of double-bond compounds, including conjugated systems, where both 1,2 and 1,4 addition are possible. A convenient method for the addition of HF involves the use of a polyhydrogen fluoride-pyridine solution.When the substrate is mixed with this solution in a solvent such as THF at 0°C, alkyl fluorides are obtained in moderate-to-high yields. 

HI, or Cdl2 iodofluorination with mixtures of AgF and U and mixtures of N-bromo amides in anhydrous HF give bromofluorination. Bromo-, iodo-, and chlorofluorination have also been achieved by treatment of the substrate with a solution of Br2,12, or an N-halo amide in polyhydrogen fluoride-pyridine while... 

Nitryl chloride (NO2CI) also adds to alkenes, to give p-halo nitro compounds, but this is a free-radical process. The NO2 goes to the less-substituted carbon. Nitryl chloride also adds to triple bonds to give the expected l-nitro-2-chloro alkenes. The compound FNO2 can be added to alkenes by treatment with HF in HNOa or by addition of the alkene to a solution of nitronium tetrafluoroborate (NOJBF4, see 11-2) in 70% polyhydrogen fluoride-pyridine solution (see also 15-37). 

Fluorocyclobutanes 8 and 9 were prepared from 1 -substituted cyclopropylmethanol derivatives in good yield by reaction with diisopropylamine/potassium fluoride/polyhydrogen fluoride-pyridine complex. This transformation forms the basis for the synthesis of ( )-2-fluorograndisol from 2-(l-isopropenylcyclopropyl)-4-mesyloxybutan-2-ol (10). ... 

Alkyl fluoroformates. These substances can be obtained in 30-75% yield by diazotization of alkyl carbamates in polyhydrogen fluoride-pyridine. 

ALKYL HALIDES r-Butyl hydroperoxides. Polyhydrogen fluoride-Pyridine. Zinc chloride. 

ETHYNYLCARBINOLS Lithium acetylide. a-FLUOROCARBOXYLIC ACIDS Polyhydrogen fluoride-Pyridine. a-FLUORO KETONES Polyhydrogen fluoride-Pyridine. 

Polyhydrogen fluoride-Pyridine (Pyridinium polyhydrogen fluoride), 5, 538-539 ... 

Dry NaNOj added to a stirred mixture of rac. tyrosine and 70%-polyhydrogen fluoride-pyridine, and the product isolated after 1 hr. stirring -> 3-(4-hydroxy-phenyl)-2-fluoropropanoic acid. Y 90%. F. e. s. G. A. Olah and J. Welch, Synthesis 1974, 652 f. reactions s. ibid. 1974, 653, 654. 

Simple alcohols and aldehydes are efficiently oxidized to carboxylic acids using solid NaMn04-H20 yields around 70% are obtained. Rearrangement products are sometimes observed in the conversion of a-amino acids to a-fluoroacids using NaNOa in polyhydrogen fluoride-pyridine/ However, this problem is effectively suppressed by the use of 48 52 (w/w) hydrogen fluoride pyridine (Scheme 2). ... 

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