Pyridine hydrofluoride

Pyridinium poly(hydroger) fluoride) Pyridine, hydrofluoride (32001-55-1),... 

Scheme 2.21 Hydrofluorination of olefins and acetylenes with 70% HF-pyridine and polyvinyl-pyridine hydrofluoride (PVPHF) [55a, 56, 61].

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). 

The Baltz-Schiemann reaction is still one of the most common methods for direct ring fluorination because of the accessibility to aminated isoquinoline derivatives. The original conditions, which involve the use of tetrafluoroboric acid (fluoroboric acid), are still often employed, [23-27] even though several modified procedures have been reported. For example, Myers synthesized 1-fluoroisoquinoline 2 by the dealkylative diazotization of 1-fcrt-bntyl-aminoisoquinoline 1 with pyridine hydrofluoride instead of HBF4 (Scheme 8) [28]. 

One of the syntheses of 198 is based on pyrazine 200 (Scheme 47) [165, 166]. Compound 200 was transformed to methoxy derivative 201 via diazotization step 201 was then subjected to Buchwald - Hartwig amination to give 202. Ester 202 was transformed to amide 203 diazotization of 203 in the presence of pyridine hydrofluoride led to the formation of fluoro derivative 204. The last step of the synthesis included deprotection of the methyl ether to give 198. 

A further modification of this method 86 was described by Neugebauer et alJ93 In this version, the nitrile was dissolved in dry liquid HF at a temperature below 0°C, instead of HC1 saturated CH2C12, to give the adduct [R1CNH]+HF2 44 (Scheme 20). This compound was reacted with a thiol to form a thioimidate hydrofluoride 45, which upon treatment with H2S/ pyridine solution provided the dithioester derivative 46. 

A modification of the Pinner reaction using liquid HF has been used to improve the yields of the dithioester products. The N-protected amino acid and peptide nitriles 6 dissolve in liquid HF at temperatures below 0°C and react with thiols to form the imidothioic acid ester hydrofluorides 7 that further react with H2S in pyridine at 0°C to form the dithioesters 8 (Scheme 2)J71 Several isotopic dithioesters have been synthesized by this method with improved yield (Table 2). The use of liquid HF at low temperature helps to dissolve the amino acid nitriles that are not very soluble under Pinner conditions (HCl-saturated CH2C12). 

Compounds 3a and c give a reversed regioselectivity compared to the analogous reactions with alkylamine hydrofluorides (sec Section 1.1.4.3.2.1.5.) whereas compound 3b gives almost equal amounts of regioisomers with 70% hydrogen fluoridc/pyridine. The low yield in cases 3d and e may be due to the solvent used. 

Some discussion of the comparison between hydrogen fluoride/pyridine and alkylamine hydrofluorides can be found in refs 92, 93. 

Good yields of fluorohydrins 4/5 can be achieved even from simple aliphatic epoxides using 70% hydrogen fluoridc/pyridine by careful control of the reaction conditions,42 - 95 but the regioselectivity may be considerably lower than with alkylamine hydrofluorides. 

In order to give the products of nucleophilic substitution by fluoride ion, the corresponding triflates 9 and 10 of the bromohydrins 6 and 7, triflic anhydride was used in the presence of pyridine and 4-dimethylaminopyridine in dichloromethane at — 35°C. A 3 2 ratio of stereoisomeric triflates was obtained no matter which starting bromohydrin was used. Then adding the triethylamine--tris(hydrofluoride) complex to the mixture at — 35 °C gave the corresponding bromofluoro-derivatives 3 and 4. ... 

Hydroch lorides. Hydrobromides, Hydriodides Diisopropylamine hydrofluoride Dimethylamine -, Di-butylamine -, Tri-methylamine -, Tri-ethylamine -, Pyridine -, Quinoline hydrochloride Pyridine hydrobromide (CHg)2NCHF2, SHF... 

Pyridine methanol. See Pyridine-3-methanol 3-Pyridinemethanol, hydrofluoride. See Nicomethanol hydrofluoride Pyridine, 3-methyl-. See P-Picoline Pyridine, 4-methyl-. Seev-Picoline Pyridine-1-oxide. See Pyridine-N-oxide Pyridine-N-oxide... 

Hydrochlorides, Hydrobromides, Hydriodides Diisopropylamine hydrofluoride Dimethylamine Di-butylamine Prime thy lamine Tri-ethylamine Pyridine -y Quinoline hydrochloride Ethyldiisopropylamine hydrobromide Pyridine hydrobromide (CH2).NCHF2, SHF H2NOHy HCl Chlorides Methiodides Benzy Itrimethy l-ammonium cyanide Quaternary ammonium halides (CH2)4N-F-y... 

Hydrochlorides, Hydrobromides, Hydriodides Diisopropylamine hydrofluoride Dimethylamine -, Di-butylamine Tri-metyhlamine Tri-ethylamine Pyridine Quinoline hydrochloride... 

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