Pentafluoroethyl Groups Research Articles

Investigations of the Tautomeric Equilibria between Phosphane Oxides and Their Corresponding Phosphinous Acids Bearing Electron‐Withdrawing Perfluoroaryl Groups

AbstractThe unusual form of a phosphinous acid can be stabilized by strongly electron‐withdrawing substituents such as trifluoromethyl and pentafluoroethyl groups. The less electron‐withdrawing pentafluorophenyl group favors the phosphane oxide tautomer (Rf)2P(O)H in the solid state, whereas in solution a solvent‐dependent equilibrium with the phosphinous acid tautomer (Rf)2POH is observed. The increasing donating ability of the solvent leads to an increasing amount of the corresponding phosphinous acid tautomer. In accord with quantum chemical calculations, the electron‐withdrawing effects of the p‐tetrafluoropyridyl and 2,4‐bis(trifluoromethyl)phenyl groups exceed the pentafluorophenyl group and should therefore be ideally suited to stabilize the corresponding phosphinous acid tautomer (Rf)2POH. The syntheses of bis(tetrafluoropyridyl)‐ and bis[2,4‐bis(trifluoromethyl)phenyl]phosphane oxide enabled the investigation of the solvent‐dependent tautomerism by NMR spectroscopy. Introduction of the tetrafluoropyridyl group shifts the tautomeric equilibrium significantly towards the phosphinous acid. Surprisingly, the comparably electron‐withdrawing but more bulky 2,4‐bis(trifluoromethyl)phenyl group favors the oxide tautomer. The experimental results have been confirmed by DFT calculations. In summary, electron‐withdrawing substituents stabilize the phosphinous acid tautomer, whereas it is destabilized by space‐demanding groups by an increased C–P–C angle.

A practical method to access enantiopure β-perfluoroalkyl-β-amino acids: diastereoselective reduction of cyclic enamino-esters

A highly practical method to access enantiopure β-perfluoroalkyl-β-amino acids was developed, which could be conducted without any expensive reagent, special apparatus/technique, nor tedious chromatographic separation. The condensation of methyl 4,4,4-trifluoro-3-oxobutanoate with ( S)-2-amino-2-phenylethanol, followed by an intramoleculer transesterification, gave an enamino-ester with a seven-membered ring structure. The hydride reduction of the cyclic enamino-ester proceeded with excellent diastereoselectivity (dr = 95:5–97:3) to give the corresponding cyclic amino-ester. The major isomer of the cyclic amino-ester was readily separated from the minor one and successfully converted into ( S)-3-amino-4,4,4-trifluorobutanoic acid (five steps, 38% overall yield, >99% ee). Concerning the key step of this synthesis, the same strategy was applicable to another substrate; the asymmetric hydride reduction of a cyclic enamino-ester with a pentafluoroethyl group also proceeded in excellent diastereoselectivity (dr = 96:4).

Stereomutation and Experimental Determination of the Relative Stability of Diastereomeric O‐Equatorial Anti‐Apicophilic Spirophosphoranes

AbstractA novel bidentate ligand based on 1,1,1,3,3,4,4,4‐octafluoro‐2‐phenyl‐2‐butanol (16) has been used to synthesize a diastereomeric pair of hydrophosphoranes (18‐exo and 18‐endo). A comparison of the structures of a series of hydrophosphoranes (18‐exo, 18‐endo, 19, and 20‐exo) obtained by X‐ray crystallography indicated that the apical P–O bond lengths were affected by the electronic properties of the oxygen atom, which can be interpreted by the “single bond/no bond resonance” concept. From the hydrophosphoranes, O‐apical (13‐exo and 13‐endo) and anti‐apicophilic O‐equatorial (12‐exo and 12‐endo) phosphoranes were synthesized. The O‐equatorial phosphoranes were irreversibly converted into diastereomeric pairs of O‐apical isomers. Kinetic measurements implied that the electronic properties of the pentafluoroethyl group are comparable to those of the trifluoromethyl group. The activation enthalpies calculated for the stereomutations enabled us for the first time to experimentally show the stability of an O‐apical isomer to be greater than that of an O‐equatorial isomer by 13.7 kcal mol–1.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Synthesis and Application of a Bidentate Ligand Based on Decafluoro‐3‐phenyl‐3‐pentanol: Steric Effect of Pentafluoroethyl Groups on the Stereomutation of O‐Equatorial C‐Apical Spirophosphoranes

1,1,1,2,2,4,4,5,5,5-Decafluoro-3-phenyl-3-pentanol was prepared by a Cannizzaro-type disproportionation reaction, and the dimetallated compound was used as a bidentate ligand, which is bulkier than the Martin ligand (1,1,1,3,3,3-hexafluoro-2-phenyl-2-propanol). A P-H spirophosphorane was synthesized by utilizing the new bidentate ligand, and the structure of the product was essentially the same as that of the P-H phosphorane with Martin ligands. Phosphoranes that exhibit reversed apicophilicity (O-equatorial) were also synthesized and could be converted into the corresponding stable stereoisomers (O-apical). The crystal structures of O-equatorial phosphoranes and the O-apical isomers were slightly affected by the steric repulsion of pentafluoroethyl groups. Kinetic measurements revealed that the stereomutation of O-equatorial methylphosphorane to the O-apical isomer was slowed. The activation enthalpy for the stereomutation of the former to the latter was higher than that of the phosphorane with Martin ligands by 5.1 kcal mol(-1).

Direct Observation of CF2 Insertion into the Carbon−Metal Bond on Cu(111)

Reflection−absorption infrared spectroscopy determined the coexistence of surface-bound trifluoromethyl (CF3) and difluorocarbene (CF2) moieties, resulting from C−I and subsequent C−F bond scission reactions below 160 K after the CF3I adsorption on Cu(111). Upon further heating, concomitant with the depletion of Cu−CF3 and CuCF2, a new surface intermediate was identified unequivocally as the pentafluoroethyl (Cu−CF2CF3) groups. This observation provides evidence for the reaction of CF2 migratory insertion into the carbon−copper bond. At about 300 K, together with the CF2 coupling pathway, the Cu−CF2CF3 species undergo a β-fluoride elimination reaction to liberate tetrafluroethylene (CF2CF2) into the gas-phase as the final product.

ChemInform Abstract: Unexpected Influence of Tetra‐ and Pentafluoroethyl Groups on the Direction of Reactions of 2‐Polyfluoroalkylchromones with 2‐Aminoethanol.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Unexpected influence of tetra- and pentafluoroethyl groups on the direction of reactions of 2-polyfluoroalkylchromones with 2-aminoethanol

2-Polyfluoroalkylchromones react with 2-aminoethanol at room temperature to give either 3-(2-hydroxyethylamino)-1-(2-hydroxyphenyl)-3-polyfluoroalkylprop-2-en-1-ones [RF = CF2H, CF3, (CF2)2OCF3 or (CF2)3CF3] or N-(2-hydroxyethyl)-2-polyfluoroalkyl-4H-chromene-4-imines [RF = (CF2)2H or C2F5].

Reaktionen Pentafluorethyl‐substituierter Bicyclo[2.1.1]hexan‐Derivate

Reactions of Pentafluoroethyl‐Substituted Bicyclo[2.1.1]hexane DerivativesThe effect of inductively electron‐withdrawing substituents on the generation of 2‐bicyclo[2.1.1]hexyl cations was probed by means of pentafluoroethyl groups. 2‐Pentafluoroethyl‐2‐bicyclo[2.1.1]hexyl brosylate (4a) and triflate (4b) were found to rearrange with formation of the analogous 1‐pentafluoroethyl‐2‐bicyclo[2.1.1]hexyl sulfonates 5a, b. Solvolytic displacement did not compete with the rearrangement but occurred on 5b at elevated temperatures. Deuterium labels revealed that the rearrangement proceeded stereospecifically, with the sulfonate departing and rebonding on the same side of the molecular plane. Complete inversion was observed during solvolysis of 5b in aqueous dioxane while some retention (16%) occurred in trifluoroacetic acid. Predominant inversion even with the analogous diazonium ion in water attests to the reluctant formation of 1‐pentafluoroethyl‐2‐bicyclo[2.1.1]hexyl cations. Solvolysis rates of 4a, b and 5b were in close agreement with those of the analogous cyano derivatives, thus confirming that the resonance interaction of α1‐cyano groups with carbocations is small.

Reaction of acceptor-substituted carbonyl compounds with diethylamino sulfur trifluoride

The reaction of carbonyl compounds with SF 4 or its derivatives like diethylamine sulfur trifluoride (DAST) is a well-established method for the introduction of fluorine into organic systems. However, in contrast to ‘normal’ aldehydes and ketones (eqn. 1; R and AH, alkyl or aryl), compounds containing an electron-withdrawing group adjacent to the carbonyl group have been used rather infrequently in carbonyl-fluorination. (Reaction with DAST have been described only for few examples.) ▪ R = alkyl, aryl A = CO 2R′, CF 3, CF 2R″ We have found that various acceptor-substituted carbonyl compounds react very easily with DAST (faster than ‘normal’ aldehydes and ketones). This opens up a facile route to α, α-difluoro-substituted carboxylic esters as well as to compounds containing pentafluoroethyl groups or tetrafluoroethylene moieties (eqn. (1). The use of this method is demonstrated in the synthesis of new liquid crystalline materials [ DE Pats 4 002 374 and 4 101600 (Aug. 1, 1991), 4 015 681 (Nov. 21,1991)] to E. Bartmann, E. Poetsch, U. Finkenzeller and B. Rieger (for Merck-Patent GmbH).

ChemInform Abstract: Nucleophilic Addition of the Pentafluoroethyl Group to Aldehydes, Ketones, and Esters.

AbstractThe aldehydes and ketones (Ia) ‐ (Ic) react with pentafluoroethyl iodide (II) in the presence of methyllithium to produce the pentafluoroethylalkanols (III).

Nucleophilic addition of the pentafluoroethyl group to aldehydes, ketones, and esters

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTNucleophilic addition of the pentafluoroethyl group to aldehydes, ketones, and estersPaul G. Gassman and Neil J. O'ReillyCite this: J. Org. Chem. 1987, 52, 12, 2481–2490Publication Date (Print):June 1, 1987Publication History Published online1 May 2002Published inissue 1 June 1987https://doi.org/10.1021/jo00388a025RIGHTS & PERMISSIONSArticle Views904Altmetric-Citations102LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Synthesis and alkaline hydrolysis of (pentafluoroethyl)imidazoles

Photochemical ring substitution of the N-trifluoroacetyl derivatives of histamine and of L-histidine methyl ester by pentafluoroethyl radical provides the corresponding 2- and 4-pentafluoroethylated products in yields of 19% and 27%, respectively. Alkaline hydrolysis converts the 2-pentafluoroethyl group to trifluoroacetyl. The reaction mechanism, involving a diazafulvene intermediate, is analogous to that elucidated for (trifluoromethyl)imidazoles; however, the pentafluoroethyl group is markedly more reactive to hydrolysis than the trifluoromethyl group. For imidazole derivatives, the ratio of reactivities is 75 at C-2 and 40 at C-4. The hydrolysis of 4-(pentafluoroethyl)histamine affords the bicyclic product, 4-(trifluoromethyl)-6,7-dihydro-1H-imidazo[4,5-c]-pyridine in 65.4% yield.

ChemInform Abstract: Enzymatic Syntheses of Chiral Building Blocks with Trifluoromethyl or Pentafluoroethyl Groups.

AbstractEine Serie optisch aktiver, Fluor enthaltender Alkohole wird durch en‐zymatische Reduktion mit Bäcker‐Hefe aus den entsprechenden Ketonen hergestellt.

Enzymatic syntheses of chiral building blocks with trifluoromethyl or pentafluoroethyl groups

Abstract A number of optically active allylic alcohols with a trifluoromethyl or a pentafluoroethyl group were prepared by the biological reduction of the corresponding ketones with active fermenting baker's yeast.

Carbene chemistry. Part II. Migration in fluoroalkylcarbenes

Photolysis of 4-diazo-1,1,1,2,2,3,3-heptafluoropentane gives heptafluoropropyl(methyl)carbene, in which migration of hydrogen takes place to give 3,3,4,4,5,5,5-heptafluoropent-1-ene in high yield. Migration of fluorine or of the pentafluoroethyl group is not observed. The photolysis of 3-diazo-1,1,2,2-tetrafluoropropane gives the corresponding carbene in which migration of the difluoromethyl group is the major reaction; other minor products are believed to arise from a cyclopropane in an excited state, formed by insertion into the γ-CH bond.The exploration of routes to 2-diazo-1,1-difluoroethane and 2-diazo-1-fluoropropane, and the n.m.r. spectra of a number of compounds containing the CHF2·CF2· group are also reported.