Organoaluminum fluorides

In this review we introduce a survey of organoaluminum fluorides with some examples of other related aluminum-fluorine compounds. A systematic overview of currently available synthetic methods for the preparation of organoaluminum fluorides is presented first. Then major examples of molecular structures of different classes of compounds are discussed in connection with their structural parameters and and NMR spectroscopic characteristics.     

A short, simple and general approach for the synthesis of (3S,4S)-3-methoxy-4-methylamino pyrrolidine and (3S,4R)-3-methoxy-4-methylamino pyrrolidine

A general and efficient stereoselective approach for the synthesis of (3S,4S) and (3S,4R)-3-methoxy-4-methylamino pyrrolidines, a part of the structure of AG-7352, a naphthyridine antitumor agent and quinoline antibacterial compounds has been described.     

Action des hydrazines fluoroalkylées sur les phosphoallènes: synthèse d’hydrazones N-fluoroalkylées β-phosphonatées

Ten phosphorylated β-hydrazones of structure R₂P(O)C(NNHR_F)CHR₂′ were prepared in 54-91% yield by heating the allenes R₂P(O)CHCCR₂′ with fluorinated hydrazines H₂NNHR_F in chloroform or methanol [R=Ph, OCH₂C(Me)₂CH₂O or OCH₂C(Me)(Pr)CH₂O, R′=H or Me and R_F=CH₂CF₃ or C₆F₅]. Two cyclohexyl derivatives were prepared similarly from R₂P(O)CHCCy. The triphenyl derivatives Ph₂P(O)CH₂C(NNHCH₂CF₃)Ph and Ph₂P(O)CH₂C(NNHC₆F₅)Ph were made in 91 and 68% yield by heating the ketones Ph₂P(O)CH₂C(O)Ph with an ethanol solution of the corresponding hydrazines. The stereochemistry of the hydrazones was determined by multinuclear NMR experiments. Compounds with C(NNHR_F)Me groups exist as a mixture of Z and E isomers, with the Z form predominating (fluorinated group syn to phosphorus). Those with C(NNHR_F)CHMe₂, C(NNHR_F)Cy or C(NNHR_F)Ph groups were formed selectively, the Z isomers being the only products. The results are explained by steric hindrance, the bulkier isopropyl, cyclohexyl or phenyl group disfavouring the E configuration. , , , NMR data, coupling constants and IR data are reported.     

First separation and characterization of cis and trans 1,2-bisaryloxy perfluorocyclobutanes

4-Bromotrifluorovinyloxybenzene (4-Br-TFVE) undergoes cyclodimerization upon heating at 150 °C affording cis and trans isomers of 1,2-bis(4-bromophenoxy)hexafluorocylcobutane. Stereoisomers were separated by selective crystallization, confirmed by single crystal X-ray, and further characterized by NMR. Remarkable difference in the solid state structures include aryl to aryl dihedral angles of 12° for the trans isomer and 88° for the cis isomer. Polymers containing roughly equal amounts of cis and trans fused perfluorocyclobutyl (PFCB) rings should be expected to have low crystallinity due to the marked difference in the two unit cells as is observed.     

H nuclear magnetic resonance spectroscopy analysis for simultaneous determination of levodopa, carbidopa and methyldopa in human serum and pharmaceutical formulations

A method utilizing NMR spectroscopy has been developed to confirm the identity and quantity of levodopa, carbidopa and methyldopa in human serum and pharmaceutical preparations. The method is based on 500 MHz proton NMR spectra of individual catecholamine molecules. Qualitative and quantitative analyses are based on resonance characteristics of the functional groups present in their structures and the integral ratio of selected signals belonging to different compounds with respect to those of an internal standard, respectively. Experiments are performed to validate the quantitative NMR method, and the linearity and reproducibility of the proposed method are verified. The detection limit of the proposed method was estimated as 4.2, 1.7 and 1.6  μg ml⁻¹ for levodopa, carbidopa and methyldopa, respectively. The recovery studies performed on human serum samples ranged from about 82-96% with relative standard deviations of <4%. The method was also applied successfully to the determination of each active compound in real pharmaceutical samples, and compared with the results obtained by the reference methods. The method is rapid, precise, accurate, and suitable for routine analyses.     

The regioselectivity of the formation of 2-pyrazolylthiazoles and their precursors from the reaction of 2-hydrazinothiazoles with 4,4,4-trifluoro-1-hetaryl-1,3-butanediones

Reaction of 2-hydrazinothiazoles 1 with 1-thienyl- and 1-furyl-1,3-butanediones 2a,b in methanol in the presence of hydrochloric acid mainly leads to a mixture of pyrazoles 3 and pyrazolines 4 or pyrazoles 3 and 5 in strong acidic conditions. Isomeric hydrazones 6 and pyrazolines 4 were formed and isolated in these reactions in the absence of hydrochloric acid. It has been shown that the regioselectivity in the reaction of diketones 2 with hydrazine 1 is governed by both the concentration of acid and the nature of substituents in the 1,3-diketones 2. Cyclization of hydrazones 6 is shown to occur under milder conditions than dehydration for pyrazolines 4. The new heterocyclic compounds were prepared and fully characterized by NMR spectra and by X-ray analysis for 3c.     

Synthesis and NMR studies of 2- and 3-fluorosubstitued five-membered heterocycles

A set of 2-fluoro- and 3-fluoro-substituted thiophenes, pyrroles and furans has been synthesized by a treatment of the corresponding lithio derivatives with N-fluorodibenzenesulfonamide. For all these compounds, and coupling constants and NMR chemical shifts have been measured. In all cases, a dramatic increase of the couplings has been observed in 2-fluoro- and 3-fluoro-substituted compounds in comparison with those measured for the parent compounds. The same is valid for measured in 3-fluoro derivatives.The DFT calculations performed for 2- and 3-fluoro-substituted compounds reproduce very well the experimental coupling values and show that the Fermi contact contribution is the main factor determining their magnitude. Also the trends observed in the NMR shieldings are well reflected in the calculated DFT data.     

Isolation of C60(CF3)n (n = 2, 4, 6, 8, 10) with high compositional purity

The high temperature reaction of C₆₀ with silver(I) trifluoroacetate followed by 500 °C sublimation and subsequent HPLC purification has led to the isolation of the five trifluoromethyl[60]fullerenes C₆₀(CF₃)_n (n=2, 4, 6, 8, 10). Four of them have >90% compositional purity. Two of the compounds, C₆₀(CF₃)₄ and C₆₀(CF₃)₆, were obtained as C₁-symmetry isomers with >90% isomeric purity, and a sample of C₆₀(CF₃)₂ also contained ca. 15-20% of a C_s-symmetry isomer of C₆₀(CF₃)₄. The new compounds were characterized by IR and EI mass spectrometry (all five compounds), NMR spectroscopy (C₆₀(CF₃)₂, C₆₀(CF₃)₄, and C₆₀(CF₃)₆), and 2D COSY NMR spectroscopy (C₆₀(CF₃)₄ and C₆₀(CF₃)₆). Calculations at the AM1 and DFT levels of theory have led to the prediction of the most likely structures for C₆₀(CF₃)₂, C₁-C₆₀(CF₃)₄, C_s-C₆₀(CF₃)₄, and the two most likely structures of C₁-C₆₀(CF₃)₆.     

Solvent effects on the O NMR chemical shifts of 4-dimethylsulfoximide-1,1,1-trifluoro-3-alken-2-ones

A multi-linear-regression analysis using the Kamlet-Abbout-Taft (KAT) solvatochromic parameters in order to elucidate and quantify the solvent effects on the chemical shifts of three 4-dimethylsulfoximide-1,1,1-trifluoro-3-buten-2-ones is reported. The predominant conformational structures of compounds has been determined by energy minimization calculations using the Austin Model (AM1) semi-empirical method, which has been used to explain the NMR chemical shifts for CO and SO groups. The chemical shifts of carbonyl and sulfoximide oxygen’s of molecules showed similar dependencies (in ppm) on the solvent polarity-polarizability and the solvent hydrogen-bond-donor (HBD) acidities. The influence of solvent hydrogen-bond-acceptor (HBA) basicities was little significant.     

Reactions of β-methoxyvinyl trifluoromethyl ketones with 2-pyridinecarboxamidrazone: A convenient route to trifluoromethylated 4,5-dihydro-1H-1-picolinoylpyrazole hydrochlorides

A new series of six 3-aryl-5-hydroxy-5-trifluoromethyl-4,5-dihydro-1H-1-picolinoylpyrazole hydrochlorides were synthesised in one-step in high yields by the reaction of β-methoxyvinyl trifluoromethyl ketones with 2-pyridinecarboxamidrazone in the presence of hydrochloric acid. The hydrochloride salts were easily converted to the respective new series of free trifluoromethylated 4,5-dihydro-1H-1-picolinoylpyrazoles using triethylamine in anhydrous diethyl ether. X-ray structure and NMR data from the pyrazole hydrochlorides are reported.     

Molecular structure and spectral properties of thionaphthalimides

The molecular structure and absorption spectra of monothio- and dithio-naphthalimides were compared to their naphthalimide analogues using AM1, PM3 and ZINDO/S semiempirical quantum chemical methods. The substitution of the 4R-naphthalimide oxygen atoms by sulphur atoms resulted in a red-shift of the absorption spectra by Δλ_max60-65 and 100-140 nm, respectively. The thionated naphthalimide derivatives do not show observable fluorescence due to intersystem crossing to the triplet -states localised at the CS groups. The -absorption bands of monothioimides are located at 525-580 nm (ε=60-80) and those for dithioimides at 535-560 nm (ε=140-390) and 628-686 nm (ε=34-68). None of these transitions are solvent sensitive. The -transitions of N-phenylthioimides have also a small contribution from -states due to a partial conjugation between CS group and π-electronic system of the N-phenyl ring. As a result, the bands of aromatic substituted N-phenylthioimides are red-shifted as compared to those of the aliphatic N-methyl-thioimides.     

Synthesis and characterisation of bis(pentafluorophenyl)antimony(V) cations, [(C6F5)2SbL3]

Pentacoordinate complex cations of the general formula [(C₆F₅)₂SbL₃]³⁺ stabilized as solid salts in combination with tetraphenylborate (BPh₄), tetrafluorobroate (BF₄) anions, where L=DMSO, Ph₃AsO, PyO, DMF, α-, β- and γ-picoline have been isolated. The newly formed complexes were characterized by elemental analysis, molar conductance measurements, solid-state IR and and NMR. From these results, a five-fold coordination around antimony was required.     

Synthesis of lariat organochalcogenoethers based on azacalix[3]arenes for the potentiometric detection of [UO2] ions

The syntheses of organochalcogen-supported azacalix[3]arenes are described in a one-pot manner in satisfactory yields. A remarkably selective potentiometric response was accomplished for uranyl ions over a variety of other metal ions, including alkali (Na⁺, K⁺), alkaline-earth (Mg²⁺, Ca²⁺, Ba²⁺), transition and heavy metal ions (Co²⁺, Ni²⁺, Cu²⁺, Ag⁺, Fe³⁺, Zn²⁺, Cd²⁺ and Pb²⁺) using an ion-selective electrode based on compound 3 incorporated into a polymeric (PVC) membrane.     

Substitution of Co in YBa2Fe3O8

The accommodation of Co in the oxygen-saturated solid-solution phase YBa₂(Fe_1−zCo_z)₃O_8+w has been investigated by powder X-ray and neutron diffraction techniques, as well as by Mössbauer spectroscopy. Of the nominal composition range 0.00?z?1.00 tested, the solid-solution limit under syntheses at 950°C in is z=0.47(5). No symmetry change in the nuclear and magnetic structures is seen as a consequence of the Co substitution, and the Co atoms are distributed evenly over the two sites that are square-pyramidally and octahedrally coordinated for w=0. The oxygen-saturated samples maintain their oxygen content roughly constant throughout the homogeneity range, showing that Co³⁺ replaces Fe³⁺. Despite the nearly constant value of w, Mössbauer spectroscopy shows that the amount of tetravalent Fe slightly increases with increasing z, and this allows Co to adopt valence close to 3.00 to a good approximation. The magnitude of the antiferromagnetic moment (located in the a,b plane) decreases with z in accordance with the high-spin states of the majority Fe³⁺ and Co³⁺ ions. Bond-valence analyses are performed to illustrate how the structural network becomes increasingly frustrated as a result of the substitution of Fe³⁺ by the smaller Co³⁺ ion. A contrast is pointed out with the substitution of cobalt in YBa₂Cu₃O₇ where it is a larger Co²⁺ ion that replaces smaller Cu²⁺.