Effets electroniques en stereochimie—II : Reduction asymetrique de benzophenones substituees

The asymmetric reduction of benzophenones p-X-C₆H₄-CO-C₆H₅ (X = CH₃, OCH₃, Br, CF₃) and p-CF₃-C₆H₄-CO-C₆H₄-p'-Z (Z = CH₃, Br) by chiral Grignard reagents p-Y-C₆H₄-CH(C₂H₅)CH₂MgCl (Y = OCH₃, CF₃) gives benzhydrols of optical purities which can reach 37%. The absolute configuration of the alcohol depends on the nature of substituents. The substituent effect is discussed through donor-acceptor interactions between the aromatic nuclei in the diastereoisomeric transition states.     

Polyterephthalates of 2,3-disubstituted butanediols-1,4: Effect of aliphatic substituents on Tg and Tm of the polyesters

Poly(2,3-dialkylbutanediol-1,4 terephthalates) with the alkyl substituents CH₃, C₂H₅, n-C₃H₇, iso-C₃H₇, n-C₄H₉, and n-C₁₀H₂₁, andn-C₁₆H₃₃ were synthesized from the corresponding 2,3-dialkylbutanediols-1,4 and dimethyl terephthalate or terephthaloyl chloride. The substituents of the butanediol-1,4 portion of the polyterephthalates influence the ¹³C NMR chemical shifts of the carbon atoms near the branching site, the glass transition (T_g), and the crystallizability. Small alkyl substituents do not change the T_g of the polymers, whereas bulky substituents such as the isopropyl group increase the T_g and long normal alkyl groups as substituents decrease the T_g of the polymers. Crystallinity in these polyterephthalates was found only with CH₃ and C₁₆H₃₃ as the 2,3-dialkyl substituents in the butanediol-1,4 portion of the polyester. This crystallinity of polyterephthalate of 2,3-di-C₁₆H₃₃ substituted butanediol-1,4 could be assigned to side-chain crystallization of the paraffinic groups.     

Proprietes chiroptiques de benzhydrols substitués—I : Rotations specifiques et configurations absolues de benzhydrols monosubstitues en 4, et de benzhydrols disubstitues en 4,4'

The resolution of monosubstituted benzhydrols p-X-C₆H₄-CHOH-C₆H₅ (X = CH₃, OCH₃, Br, CF₃), and the absolute configuration of these and of disubstituted benzhydrols p-CF₃-C₆H₄-CHOH-C₆H₄-Y-p' (Y = Br, CH₃) are reported.     

The torsional barrier in aromatic carbonyl compounds. VI. Carbon-13 and 1H DNMR study of protonated alkyl and haloalkyl p-tolyl ketones

The free energy of activation of the torsional barrier around the phenyl–carbonyl bond in a series of stable protonated α-substituted p-methylacetophenones (p-tolyl- where R = CH₃, C₂H₅, i-C₃H₇, t-C₄H₉, CH₂Cl, CHCl₂, CCl₃, CH₂F, CHF₂, CF₃ and CH₂Br) has been evaluated by complete lineshape analysis of ¹³C or proton low temperature NMR spectra. α-Substitution by an alkyl group leads to a decrease of the barrier height due to both steric and electronic effects. For the halo compounds, steric and electronic effects of the substituents are in competition, leading to a very high ΔG^≠ value in protonated α,α,α-trifluoro-p-methylacetophenone (63.2 kJ mol^?1). In addition, the twist angle of the protonated carbonyl group has been tentatively evaluated by the use of the (modified) Stothers's method.     

Diastereoselective addition of organomanganese compounds to α-alkoxysubstituted propanals

Reactions of organomanganese compounds R¹MnI (R¹ = Ph, 4-MeC₆H₄-, Me, Bu,n-C₇H₁₅, BuC=C, PhOC), prepared from R¹Li and Mnl₂ in Et₂O, with aldehydes MeCH(OR²)CHO (R² = CH₂Ph, CH₂OMe, CH₂OCH₂Ph) affordthreo-alcohols MeCH(OR²)CH(OH)R¹ with high diastereoselectivity. The interactions of phenylmanganese derivatives PhMnX (X = Cl, Br, I), Ph₂Mn, and Ph₃MnLi with 2-benzyloxypropanal were used as examples for studying the influence of reagent and solvent nature on addition diastereoselectivity.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 178–181, January, 1993.     

Synthesis and configurational assignment of diastereomers ofcloso-3,3-[η2,3-(2-methylenebicyclo[2.2.1]hepta-2,5-dien-2-yl)]-1-benzyl-3,1,2-dicarbollylrhodium complexes

The previously synthesized mixture of diastereomeric complexescloso-3,3-(η^2,3-C₇H₇CH₂)-1-(PhCH₂)-3,1,2-RhC₂B₉H₁₀ was separated by TLC on silica gel into individual diastereomers, whose stereochemistry and relative configurations were determined by X-ray diffraction analysis. Triplet- and quadruplet-like signals are marked with an asterisk Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2069–2070, November, 1997.     

Studies on sulfinatodehalogenation. XX. Sodium dithionite-initiated addition of per- and polyfluoroalkyl iodides to cyclic enol ethers and chemical conversions of the products

Per- and polyfluoroalkyl iodides [R_FI, R_F=Cl(CF₂)₄, 1a ; Cl(CF₂)₆, 1b ; Cl(CF₂)₈, 1c ; n-C₆F₁₃, 1d ; n-C₈F₁₇, 1e ] reacted with cyclic enol ethers such as 2,3-dihydrofuran (2) and 3,4-dihydro-2H-pyran (3) in aqueous acetonitrile in the presence of sodium dithionite and sodium bicarbonate at room temperature (10–15°C) to give the corresponding 2-(F-alkyl) hemiacetals in high yields. The adducts were oxidized with Ce(NH₄)₂(NO₃)₆ in acetonitrile or reduced with LiAlH₄ in ether to form the corresponding 2-(F-alkyl)lactones or diols respectively in good yields. In the presence of p-toluenesulfonic acid, the adducts were refluxed in benzene and CH₃CN to produce the corresponding 2,3-dihydro-4-(F-alkyl) furan and 3,4-dihydro-5-(F-alkyl)-2H-pyran. This is a new and effective method for preparing these useful organofluorine compounds.     

Synthesis and Electrochemical Behavior of Some 1H-3-Methyl-4-ethoxycarbonyl-5-(benzylidenehydrazino)pyrazoles

Summary. 1H-3-Methyl-4-ethoxycarbonyl-5-(benzylidenehydrazino)pyrazoles are key intermediates in obtaining various heterocyclic systems including pyrazolotriazoles. We present the voltammetric behavior of these compounds in nonaqueous media, with the following para substituents grafted on the benzene ring: –N(CH₃)₂, –OH, –OCH₃, –F, –Cl, –CF₃, –NO₂, as well as of the novel compounds with –Br, –I, and –SCH₃ in the para position, in order to elucidate the influence of the various substituents on the mechanism of anodic oxidation.     

Fluorinated phosphorus compounds: Part 9. The reactions of bis(fluoroalkyl) phosphorochloridates with oxygen nucleophiles

Twenty nine bis(fluoroalkyl) phosphates (R_FO)₂P(O)OR were prepared in 18-75% yield by treating phosphorochloridates (R_FO)₂P(O)Cl, where R_F was HCF₂CH₂, HCF₂CF₂CH₂, H(CF₂)₄CH₂, C₂F₅CH₂, C₃F₇CH₂, (CF₃)₂CH, (FCH₂)₂CH and (CH₃)₂CF₃C with methanol, ethanol, propanol and isopropanol in diethyl ether in the presence of triethylamine. The bulky chloridate [(CH₃)₂CF₃CO]₂P(O)Cl reacted with methanol, ethanol and propanol, but not with isopropanol - even on heating in the presence of the catalyst 4-dimethylaminopyridine - due to steric hindrance at phosphorus. The relative reactivities of three of the chloridates decreased in the order [(CF₃)₂CHO]₂P(O)Cl > [(FCH₂)₂CHO]₂P(O)Cl > [(CH₃)₂CF₃CO]₂P(O)Cl. Also described is the synthesis of phosphates (CF₃CH₂O)₂P(O)OCH₂R, where R = CH₂Br, CH₂Cl, CH₂F and CHF₂, and diphosphates [H(CF₂)_nCH₂O]₂P(O)OCH₂(CF₂)₂CH₂OP(O)[OCH₂(CF₂)_nH]₂, where n = 1, 2 and 4.     

β-Tricarbonyl compounds. I. 2,4-Disubstituted 1,3-cyclopentanediones

Summary Stable enolic isomers of 2-aroyl-4-aracyl-1,3-cyclopentanediones such as3 and4 were prepared by condensation of aryl methyl ketones and diethyl maleate using an excess of sodium ethoxide (Aryl=C₆H₅, 4-C₆H₄CH₃, 4-C₆H₄Br and 4-C₆H₄Cl).

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-Tricarbonyl Verbindungen. I. 2,4-Disubstituierte 1,3-Cyclopentandione

Zusammenfassung Stabile Enol-Isomere von 2-Aroyl-4-aracyl-1,3-cyclopentandionen wie3 und4 wurden durch Kondensation von Arylmethylketonen und Diethylmaleat mit einem Überschuß von Natriumethoxid dargestellt (Aryl=C₆H₅, 4-C₆H₄CH₃, 4-C₆H₄Br und 4-C₆H₄Cl).

     

Kinetics for the gas‐phase reactions of OH radicals with the hydrofluoroethers CH2FCF2OCHF2, CHF2CF2OCH2CF3, CF3CHFCF2OCH2CF3, and CF3CHFCF2OCH2CF2CHF2 at 268–308 K

Rate constants were determined for the reactions of OH radicals with the hydrofluoroethers (HFEs) CH₂FCF₂OCHF₂(k₁), CHF₂CF₂OCH₂CF₃ (k₂), CF₃CHFCF₂OCH₂CF₃(k₃), and CF₃CHFCF₂OCH₂CF₂CHF₂(k₄) by using a relative rate method. OH radicals were prepared by photolysis of ozone at UV wavelengths (>260 nm) in 100 Torr of a HFE–reference–H₂O–O₃–O₂–He gas mixture in a 1‐m³ temperature‐controlled chamber. By using CH₄, CH₃CCl₃, CHF₂Cl, and CF₃CF₂CF₂OCH₃ as the reference compounds, reaction rate constants of OH radicals of k₁ = (1.68) × 10^?12 exp[(?1710 ± 140)/T], k₂ = (1.36) × 10^?12 exp[(?1470 ± 90)/T], k₃ = (1.67) × 10^?12 exp[(?1560 ± 140)/T], and k₄ = (2.39) × 10^?12 exp[(?1560 ± 110)/T] cm³ molecule^?1 s^?1 were obtained at 268–308 K. The errors reported are ± 2 SD, and represent precision only. We estimate that the potential systematic errors associated with uncertainties in the reference rate constants add a further 10% uncertainty to the values of k₁–k₄. The results are discussed in relation to the predictions of Atkinson's structure–activity relationship model. The dominant tropospheric loss process for the HFEs studied here is considered to be by the reaction with the OH radicals, with atmospheric lifetimes of 11.5, 5.9, 6.7, and 4.7 years calculated for CH₂FCF₂OCHF₂, CHF₂CF₂OCH₂CF₃, CF₃CHFCF₂OCH₂CF₃, and CF₃CHFCF₂OCH₂CF₂CHF₂, respectively, by scaling from the lifetime of CH₃CCl₃. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 239–245, 2003     

Synthesis and characterization of some lanthanide(III) chelates of some schaffer acid azo dyes

Summary A series of trivalent lanthanide chelates of the type [Ln(PHNSA) (H₂O) _n ] (2 Cl) (whereLn ³⁺=Pr, Nd, Sm, Eu, Gd, Dy, Er, Yb or Lu;PHNSA=2-(X)-phenylazo-2-hydroxynaphthalene-6-sulphonic acid;X=H, Cl, OCH₃, CH₃ and SO₃H) have been synthesized and characterized by elemental and thermal analysis, molar conductance, IR,¹H NMR (for diamagnetic complexes), electronic spectra and magnetic susceptibility measurements. IR data along with those of the¹H NMR unequivocally proved that the coordination of the ligands to the metal ions took place in a bidentate fashion through the oxygen of the hydroxyl group and the nitrogen of the azo group. The magnetic moment values showed little deviation from Van Vleck values.

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Synthese und Charakterisierung einiger Lanthaniden(III)-Chelate von Schaffersäure-Azofarbstoffen

Zusammenfassung Es wurde eine Reihe von dreiwertigen Lanthanidenchelaten des Types [Ln(PHNSA) (H₂O) _n ] (2 Cl) (mitLn ³⁺=Pr, Nd, Sm, Eu, Gd, Dy, Er, Yb oder Lu undPHNSA=2-(X)-Phenylazo-2-hydroxynaphthalin-6-sulphonsäure,X=H, Cl, OCH₃, CH₃ und SO₃H) synthetisiert und mittels Elementar- und thermischer Analyse, molarer Leitfähgigkeit, IR,¹H-NMR (für diamagnetische Komplexe), Elektronenspektren und Messungen der magnetischen Suszeptibilität charakterisiert. Die IR-Daten zusammen mit¹H-NMR-Befunden zeigten eindeutig, daß die Koordinierung der Liganden zum Metallion zweizähnig durch den Sauerstoff der Hydroxylgruppe und den Stickstoff der Azo-Gruppe erfolgt. Die magnetischen Momente zeigten nur eine geringe Abweichung von den Van Vleck-Werten.

     

1,1,1,4,5,5,5-Heptafluoro-4-(trifluoromethyl)-2,3-pentanedione,a potent reagent for the synthesis of cyclic λ5σ5 phosphoranes

1,1,1,4,5,5,5-Heptafluoro-4-(trifluoromethyl)-2,3-pentanedione reacted with λ³σ³-phosphorus compounds, PR¹R²R³ (R¹ = CF₃, R² = R³ = Me, iPr, NEt₂; R¹ = NCO, R² = R³ = OMe, OEt, R²−R³ = OCH₂CH₂O, OCMe₂CMe₂O; R¹ = OSiMe₃, R² = R³ = OEt; R¹ = NEt₂, R² = R³ = OCH₂CF₃; R¹ = R² = Et₂N, R³ = OCH₂CF₃, OCH(CF₃)₂, OCH₂Ph, OC₆F₅) to give new 1,3,2λ⁵σ⁵-dioxaphospholenes. The first λ⁵σ⁵ phosphoranes with an OCN group bonded to phosphorus were obtained. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:109–113, 1998     

Synthesis of polyphosphazenes bearing alkoxyethoxy and trifluoroethoxy groups

The synthesis of various phosphoranimines including (CH₃OCH₂CH₂O) (CF₃CH₂O)₂P?N? Si(CH₃)₃, (CH₃OCH₂CH₂OCH₂CH₂O) (CF₃CH₂O)₂P?N? Si (CH₃)₃, (CH₃OCH₂CH₂O)₂(CF₃CH₂O) P?N? Si(CH₃)₃, and (CH₃OCH₂CH₂OCH₂CH₂O)(CF₃CH₂O) P?N? Si(CH₃)₃ via the Staudinger reaction of (CH₃)₃SiN₃ with the suitably substituted phosphite is reported. These monomers were polymerized using tetra-n-butylammonium fluoride and N-methylimidazole in various solvents at several temperatures. In situ ³¹P-NMR kinetic studies and M_n versus time studies were also performed for the monomers to understand the propagation mechanism. © 1994 John Wiley & Sons, Inc.     

New partially fluorinated epoxides by oxidation of olefins with sodium hypohalites under phase transfer catalysis

Partially fluorinated epoxides can be readily prepared by oxidation of the corresponding olefins by NaOCl (or NaOBr) under phase transfer catalysis (PTC) conditions. Oxidation of CH₂C(CF₃)₂ at 0-5 °C leads to the formation of 2,2-bis(trifluoromethyl)oxirane in 65-75% yield. (CF₃)₂CCHCH₂X (X=Cl or Br) were converted into the corresponding epoxides in 24-31% yield by the action of NaOCl and NaOBr, respectively. Baylis-Hillman adducts of fluorinated ketones and esters of acrylic acid CH₂C[C(OH)(CF₂X)Y][C(O)OR] [X=F or Cl, Y=CF₃, CF₂Cl or C(O)OCH₃ and R=CH₃ or C(CH₃)₃] were converted into α-hydroxyepoxides in 47-84% yield under action of NaOCl in the presence of PT catalyst. Oxidation of tert-butyl ester of α-trifluoromethylacrylic acid by NaOCl rapidly proceeds at ambient temperature with formation of epoxide in 75% yield. Oxidation of (C₂F₅)₂CCHC₃F₇ results in the high yield formation of trisubstituted epoxide.     

Protonenresonanzuntersuchungen an Aminoboranen—II: Einflüsse von para-Phenylsubstituenten auf die Rotationsbarriere um die N?B-Bindung

The electronic influence of substituents on the free enthalpy of rotation around the N? B bond in aminoboranes was investigated in two series of compounds: (a) (CH₃)₂N?BCl (phenyl-p-X), containing the para-phenyl substituent at the boron atom, and (b) (p-X-phenyl)CH₃N?B(CH₃)₂, containing the para-phenyl substituent at the nitrogen atom of the N? B linkage (X = ? NR₂, ? OCH₃, ? C(CH₃)₃, ? Si(CH₃)₃, ? H, ? F, ? Cl, ? Br, ? I, ? CF₃ and ? NO₂). By comparing the rotational barriers in corresponding compounds of both series, a reverse effect of the substituents could be observed. Electron-withdrawing substituents in the para position of the phenyl ring increase the ΔG_c^≠ if the phenyl group is attached to the boron atom; on the other hand, a lower ΔG_c^≠ is observed if the phenyl ring is bonded to the nitrogen atom of the N? B system. Substitution of the phenyl ring with electron-donating substituents in the paraposition exerts the opposite effect. Within each series of compounds, the differences of ΔG_c^≠ values [δ(ΔG_c^≠) = ΔG_c^≠ (X) ? ΔG_c^≠ (X = H)] between substituted and unsubstituted compounds can be explained in terms of inductive and mesomeric effects of the ring substituents and can be correlated with the Hammett σ constant of each substituent. A comparison of the slopes of the plotted lines shows that the influence of the ring substituents is more pronounced in compounds with N-phenyl-p-X than in those with B-phenyl-p-X.     

NEW CYCLIC AND POLYMERIC PHOSPHAZENES DERIVED FROM N-SILYLPHOSPHORANIMINES

Silicon-nitrogen-phosphorus compounds of the type Me ₃ SiN═PR(R′)X(X= Cl, Br, OCH₂CF ₃ , OPh), known as N-silylphosphoranimines,are useful precursors to both cyclic and polymeric phosphazenes.Depending on the leaving group (X), thermolysis reactions afford either cyclic trimers, [N═PR(R′)] ₃ (when X = Cl, Br), or linear polymers,[N═PR(R′)]_n (when X = OCH ₂ CF ₃ or OPh). Treatment of the P-trifluoroethoxy and P-phenoxy derivatives, Me ₃ SiN═PR(R′)X (X = OCH ₂ CF ₃ , OPh), with alcohols at lower temperature usually results in the formation of cyclic phosphazene trimers via silyl ether elimination. Recently, we have applied these synthetic methods to the preparation of some new phosphazene systems including a series of 4-aryl-functionalized trimers and polymers and a variety of non-geminal, mixed-substituent cyclic trimers. Representative examples of the synthesis, structural characterization, and reactivity of these new phosphazenes and their Si─N─P precursors are reported here.     

Unexpected open-chain molecular structure of a titanocenyl-substituted dimethyl ether

Reaction of (η-C₅H₄CH₃)₂TiCl₂ with CH₃OCH₂MgCl yielded (η-C₅H₄-CH₃)₂Ti(Cl)CH₂OCH₃ (2a). Complex 2a crystallizes in space group P2₁/n with cell constants a 8.162(1), b 11.004(2), c 15.297(2) Å, β 96.40(1)°. In contrast to the three-membered metallacyclic zirconium compound of analogous composition (η-C₅H₅)₂Zr(Cl)CH₂OCH₃ (1), the titanocenyl-substituted ether 2a has an open-chain (η¹-O“-outside”) type structure.     

Carbon-13 NMR spectra of some o-carbonyl benzeneselenenyl derivatives

The ¹³C NMR signals have been assigned for some ortho-carbonyl benzene-selenenyl derivatives, COR.C₆H₄. Sex, where R = H, CH₃, OCH₃ and OC₂H₅ and X = Cl, Br, CN, SCN, SeCN and CH₃. The effects of the nature of R and X have been discussed.     

Fluordiazadiphosphetidine, 10. Mitt.: Die Reaktion von 1,3-Dialkyl-2,2,2,4,4,4-hexaflouro-1,3,2λ5,4λ5-diazadiphosphetidine mitN-Trimethylsilylmethylamin

Reaction of (RNPF₃)₂ compounds (R=CH₃, C₂H₅,n-C₃H₇,n-C₄H₉,i-C₄H₉) withN-trimethylsilyl-methylamine leads to nucleophilic substitution of one or two fluorine atoms by the methylamino group, depending on the molar amounts of the reactants. In the case ofR=CH₃, two by-products are formed: in the first step a compound with coordination numbers IV, V and VI for the three phosphorus atoms in C₅H₁₇F₇N₅P₃ and in the second step a monospiroflourodiaza-⁵, ⁵-diphosphetidine.

9. Mitteilung:Utvary, K., Kubjacek, M., Varmuza, K. Z. anorg. allg. Chem.458, 281 (1979).