Hydrogen Fluoride-pyridine Research Articles

SIMPLE SYNTHESIS OF GLYCOSYL FLUORIDES

Abstract Treatment of 1-unprotected or -O-acetylated sugar derivatives with a hydrogen fluoride–pyridine mixture affords the corresponding 1-fluoro derivatives in high yields.

Chemistry of organo halogenic molecules, LXXV. Polymer-supported hydrogen fluoride

Polymer-supported hydrogen fluoride prepared by reaction of hydrogen fluoride with crosslinked poly(styrene- co -4-vinyl- pyridine) containing 40–45 mol % of 4-vinylpyridine did not react with trans -stilbene, 1,2-diphenylacetylene, and cyclohexanol under various conditions, whereas 1-phenyl-1-hydroxy- 4-tert-butylcyclohexane was converted to 1-phenyl-4-tert-butylcyclohexene. Bromofluorination of various phenyl-substituted olefins with N-bromosuccinimide in the presence of polymer supported hydrogen fluoride in methylene chloride proceeds with Markovnikov type regioselectivity. Fluorination and halofluorination of norbornene with xenon difluoride or N-bromosuccinimide or N-chlorosuccinimide in the presence of polymer- supported hydrogen fluoride resulted in up to five products, with a large increase in halonortricyclane formation, compared to reactions in the presence of hydrogen fluoride-pyridine. Polymer-supported hydrogen fluoride, in comparison to hydrogen fluoride-pyridine, enhanced the endo attack of the electrophile on norbornadiene by fluorination or halofluorination.

New 9,10-seco-steroids from 11β-hydroxy-8β,9-epoxy-derivatives

Reaction of readily available 11β-hydroxy-8β, 9-epoxy-steroids with hydrogen fluoride-pyridine gave the corresponding 9.10-seco-derivatives in good yields.

Effet de la concentration en acide fluorohydrique dans la pyridine sur la stereoselectivite de la fluorobromation de cinnamates d'ethyle substitues.

Abstract Bromofluorination of six substituted ethylcinnamates (e.g. YC6H4CXCHCO2Et; Y = X = H, E and Z isomers; Y = mNO2, X = H; Y = pOCH3, X = H; and Y = H, X = Cl, E and Z isomers) with N-bromosuccinimide (NBS) in hydrogen fluoride-pyridine or hydrogen fluoride-tetrahydrofuran (several molar ratios), giving the Markovnikov-type regioselectivity has a stereoselectivity depending on several factors: the nature of the substituent (X or Y), the solvent (pyridine or THF) and mainly the hydrogen fluoride- solvent molar ratio. The variable importance of the complexation of the carbenium ion YC6H4C+XCHBrCO2Et as a complex between the olefin and NBS- hydrogen fluoride can give an interpretation of the influence of these factors on stereoselectivity.

Influence of the hydrogen fluoride-pyridine molar ratio on the regio- and stereo-selectivity in several fluorination reactions

We used the hydrogen fluoride-pyridine mixture of different molar ratio as a solvent for different fluorination reactions: 1. (i) bromofluorination of unsubstituted and substituted ethyl cinnamates ZC 6H 4C(2)XC(1)HCO 2Et with N-bromosuccinimide; 2. (ii) fluorodeamination of α-amino-esters RR′C(2)HC(1)H(NH 2)CO 2Et with sodium nitrite; 3. (iii) fluorodehydroxylation of alkyl-phenyl carbinols Ph C(2)H(OH)C(1)HRR′. The regiochemistry and the stereochemistry of the reaction products were unambiguously established by 13C and 19F NMR spectroscopy. The influence of the HF:pyridine molar ratio on the regio- and stereo-selectivity can be described as the influence of solvation by the solvent mixture of the cationic intermediates in the reactions (bridged or open-chain carbenium ions): hindrance to free rotation of the C(1)C(2) bond in the carbenium ion, mono or bifacial attack of this ion or rearrangement of the carbenium ion (positive charge on carbon C(1) or C(2). The importance of this solvation is depending on the HF:pyridine molar ratio and on the nature of the substituents (Z, X, R or R′).

New synthetic routes to β-fluoro-α-aminoacids A - from aziridinecarboxylates

Abstract Synthesis of 1-trityl-2-phenylaziridine, 1-trityl-2-methylaziridine and 2-methylcarboxylates of 1-tritylaziridine, 1-trityl-3-methylaziridine, 1-trityl-3-phenylaziridine by reacting N-triphenylmethyl-α-chloroamines with KF in acetonitrile under reflux is described. Functionalized aziridines opened with hydrogen fluoride in pyridine (70 %) give isobutyl 3-fluoroalanine, methyl-3-fluorophenylalanine and methyl 2-amino-3-fluorobutyrate. N.M.R. 1 H and 19 F are discussed. The following reactions get the compounds in the table.

Formation d'aziridines dans KF/acetonitrile - obtention de 3-fluoro amino-acides par ouverture avec HF/Py

Synthesis of 1-trityl-2-phenylaziridine, 1-trityl-2-methylaziridine and 2-methylcarboxylates of 1-tritylaziridine,1-trityl-3-methylaziridine, 1-trityl-3-phenylaziridine by reacting N-triphenylmethyl-α-chloroamines and methyl esters of N-triphenylmethyl-O-mesylsulfonyl-α-aminoacids with KF in acetonitrile under reflux is described. Functionalized aziridines opened with hydrogen fluoride in pyridine (70 %) give isobutyl 3-fluoroalanine, methyl 3-fluorophenylalanine and methyl 2-amino-3-fluorobutyrate.

ChemInform Abstract: A MILD AND EFFICIENT METHOD OF AROMATIC FLUORINATION

AbstractDie Aryltriazene (I) werden mit 70%igem Fluorwasserstoff/Pyridin zu den Arylfluoriden (II) zersetzt.

ChemInform Abstract: CHEMISTRY OF ORGANO HALOGENIC MOLECULES. XLVIII. STEREOCHEMISTRY OF HALOFLUORINATION OF 1,2‐ AND 1,4‐DIHYDRONAPHTHALENE

AbstractDie Halofluorierung des Dihydronaphthalins (III) erfolgt regioselektiv entsprechend der Markownikoff‐Regel und ist stereospezifisch anti; das gebildete Addukt (I) isomerisiert sich bei längerer Reaktion zu syn‐Produkten (IV), die unter basischen Bedingungen Halogenwasserstoff eliminieren [→(V)].

Chemistry of Organo Halogenic Molecules. XLVIII. Stereochemistry of Halofluorination of 1,2- and 1,4-Dihydronaphthalene

Abstract Halofluorination of 1,2-dihydronaphthalene with a mixture of N-chlorosuccinimide or N-bromosuccinimide or N-iodosuccinimide–hydrogen fluoride–pyridine in ether proceeds with Markovnikov type regioselectivity. The reaction is stereospecifically anti, the anti adduct isomerizing to syn products under the reaction conditions. The elimination of hydrogen halide under basic conditions occurs only from the syn adduct, thus forming 1-fluoro-3,4-dihydronaphthalene. Halofluorinations of 1,4-dihydronaphthalene also occur stereospecifically anti, and elimination under basic conditions gives naphthalene.

A mild and efficient method of aromatic fluorination

Aromatic fluorides are prepared in high yield by treatment of aryltriazenes with 70% hydrogen fluoride in pyridine at 0–80 °C.

Reactions of 4β,5-epoxy-5β-androstan-3-ones with hydrogen fluoride in pyridine

4β,5-Epoxy-5β-androstane-3,17-dione ( 1a ), 17β-hydroxy-4β,5-epoxy-5β-androstan-3-one ( 1b ) and 17β-acetoxy-4β,5-epoxy-5β-androstan-3-one ( 1c ) were treated with anhydrous hydrogen fluoride in pyridine (70% solution) at 55° and yielded the corresponding 4-en-4-ols e.g. 4-hydroxy-4-androstene-3, 17-dione ( 2a ). As the reaction temperature was lowered each epoxide formed a second product which, at −75°, was the major component of the reaction mixture and was identified as the 5α-fluoro-4α-ol derivative of the parent enone, e.g. 4α-hydroxy-5-fluoro-5α-androstane-3,17-dione ( 3a ). These fluorohydrins are thermally unstable, losing hydrogen fluoride. The acetates of the fluorohydrins were also prepared, characterized, and shown to be more stable than the parent alcohols.

Stereochemistry of bromofluorination of phenyl-substituted olefins

Bromofluorination of phenyl-substituted olefins, e.g. 1,1-diphenylethylenes, β-alkylstyrenes, and stilbene, with N-bromosuccinimide–hydrogen fluoride–pyridine in ether proceeds with Markovnikov-type regioselectivity. The reaction is sterospecific (anti) for trans- and nonstereospecific for cis-olefins.