Trifluoromethyl-containing pyrazolinyl (p-tolyl) sulfones: The synthesis and structure of promising antimicrobial agents

The regiospecific synthesis of a novel series of nine 4-phenyl- and 3-alkyl(aryl)-5-hydroxy-5-trifluoromethyl-4,5-dihydro-1H-1-tosylpyrazoles (pyrazolinyl p-tolyl sulfones), as well as their antimicrobial activity against yeast, such as fungi, bacteria, and alga are reported. The 1-p-tosyl-2-pyrazolines were obtained from the cyclocondensation reaction of 3-phenyl- and 4-alkyl(aryl)-1,1,1-trifluoro-4-alkoxy-3-alken-2-ones, [where alkyl = H, Me and aryl are -C₆H₅, 4-CH₃C₆H₄, 4-OCH₃C₆H₄, 4-FC₆H₄, 4-ClC₆H₄, 4-BrC₆H₄,] with p-tosylhydrazine in a yield of 58-92% when toluene was employed as solvent. The best activity was obtained when the structure possessed a 4-fluorophenyl substituent linked at the carbon-3 of the pyrazoline ring. Subsequently, the dehydration reaction of 3-(4-fluorophenyl) substituted 2-pyrazoline with thionyl chloride/pyridine in benzene as solvent furnished the corresponding 1H-pyrazole in only a moderate yield (49%).     

Allylic alkylation and amination using mixed (NHC)(phosphine) palladium complexes under biphasic conditions

A dramatic improvement of the catalytic activity was observed when a phosphine was added in allylic alkylation reactions catalyzed by (NHC)Pd(η³-C₃H₅)Cl complexes. Consequently, several palladium complexes, generated in situ from different NHC-silver complexes, [Pd(η³-C₃H₅)Cl]₂ and PPh₃, were tested in this reaction to evaluate their potential. High reaction rates and conversions could be obtained with this catalytic system in the alkylation of allylic acetates with dimethylmalonate, particularly under biphasic conditions using water/dichloromethane and KOH 1 M as the base. These conditions are experimentally more convenient and gave higher reaction rates than the classical anhydrous conditions (NaH/THF). In this system, the phosphine is essential since no conversion was obtained when it is not present. The steric hindrance of the carbene ligand has a great influence on the activity and the stability of the catalytic system. The best NHC ligands for this reaction are either 1-mesityl-3-methyl-imidazol-2-ylidene or 1-(2,6-diisopropylphenyl)-3-methyl-imidazol-2-ylidene which are less bulky among the NHC tested. These two ligands led in 5 min to a complete conversion at 20 °C. The Pd-catalyzed allylic amination reaction using (E)-1,3-diphenylprop-3-en-yl acetate and benzylamine was also tested with (NHC)(PPh₃)Pd complexes and under the biphasic conditions. This reaction was found to be slower than the alkylation with dimethylmalonate but a complete conversion could be reached in 6 h at 20 °C using K₂CO₃ 1 M as the base. NMR experiments indicated that mixed (NHC)(PPh₃)Pd complexes are formed in situ but their structure could not be established exactly.     

Attachment of metal trications to peptides

Gas-phase complexes of triply charged metal ions with peptides may be readily produced using electrospray ionization, including for small peptides such as bradykinin and peptides with no basic residues such as insulin chain A. Attachment without charge-reduction is demonstrated for all trications studied: La(3+), Al(3+), Ga(3+), Fe(3+), V(3+), and Cr(3+). The intensities of adducts are often comparable to, or even exceed, those of protonated analogs in any charge state.     

Addition of activated olefins to cyclic N-acyliminium ions in ionic liquids

Organoindate(III) ionic liquid (BMI·InCl₄) was successfully employed in the nucleophilic addition of allyltrimethylsilane, silyl enol ethers and ketene silyl acetals to in situ generated cyclic N-acyliminium ions at room temperature without the need of an external Lewis acid. The corresponding α-substituted heterocycles were obtained in good yields and the recovered ionic liquid phase could be reused at least three times.     

An efficient two-step total synthesis of the quaterpyridine nemertelline

Regioselective and univocal Suzuki cross-coupling reactions performed on halopyridinyl boronic acids provide a flexible and versatile route to a multigram scale synthesis of 2,2'-dichloro-3,4'-bipyridine 14, which allows couplings with excess pyridin-3-yl boronic acid to give a new and efficient two-step rapid synthesis of nemertelline, the quaterpyridine neurotoxin isolated from a Hoplonemertine sea worm.     

Design,scope and mechanism of highly active and selective chiral NHC–iridium catalysts for the intramolecular hydroamination of a variety of unactivated aminoalkenes

Chiral, cationic NHC–iridium complexes are introduced as catalysts for the intramolecular hydroamination reaction of unactivated aminoalkenes. The catalysts show high activity in the construction of a range of 5- and 6-membered N-heterocycles, which are accessed in excellent optical purity, with various functional groups being tolerated with this system. A major deactivation pathway is presented and eliminated by using alternative reaction conditions. A detailed experimental and computational study on the reaction mechanism is performed providing valuable insights into the mode of action of the catalytic system and pointing to future modifications to be made for this catalytic platform.

Chiral, cationic NHC–iridium complexes are introduced as catalysts for the intramolecular hydroamination reaction of unactivated aminoalkenes.     

Strain-dependence of the electronic properties in periodic quadruple helical G4-wires

The electronic structure of periodic quadruple helix guanine wires, which mimic G4-DNA molecules, was studied as a function of the stacking distance between consecutive planes, by means of first principles density functional theory calculations. We show that, whereas for the native DNA interplane separation of 3.4 A the HOMO- and LUMO-derived bands are poorly dispersive, the bandwidths can be significantly increased when compressive strain is applied along the helical axis. Our findings indicate that efficient band conduction for both holes and electrons can be supported by such wires for stacking distances below 2.6 A, which imply a huge axial deformation with respect to double and quadruple helices in solutions and in crystals.     

The coordination chemistry of enantiopure diimines derived from 1-phosphanorbornadiene-2-carboxaldehydes

The reaction of trans-1,2-diaminocyclohexane with enantiopure (R)-2-formyl-1-phosphanorbornadiene (1) takes place with efficient kinetic resolution and gives an easily separable mixture of the corresponding (S,S)-bis-imine (3) and (R)-mono-imine (4). The absolute configuration of 3 has been established by X-ray crystal structure analysis. The coordination chemistry of enantiopure 3 with Pd(II), Rh(I), and Ru(II) has been investigated. The reaction of [PdCl₂(cod)] mainly affords a binuclear complex 6 whose structure has been established by X-ray analysis. One unit is coordinated to one P and one PdCl⁺ unit is tricoordinated to the other P and the two N. The two square planar units are parallel and the Pd?Pd distance is 3.1787(5) Å. The reaction of [RhCl(cod)]₂ gives the very reactive tetracoordinate cationic [Rh(P₂N₂)]⁺ species 7 which is able to activate one C-Cl bond of chloroform to give the dichloromethyl-Rh complex (8) whose octahedral structure has been ascertained by X-ray analysis.     

Synthesis of novel 1,3,4-benzotriazepine derivatives from 4-oxo-3,1-benzoxazine and 3,1-benzothiazine-2-carbonitriles

Synthesis of novel oxygen and sulfur containing 1,3,4-benzotriazepine derivatives was performed via 3,1-benzoxazine and 3,1-benzothiazine intermediates obtained from Appel's salt chemistry. We observed that the sulfur containing precursors reacted differently than their oxygenated congeners and, after rearrangement, afforded novel heterocyclic compounds (e.g., benzoxazin-4-thione and 2-cyano-1,3,4-triazepine).     

Ionic liquid crystal precursors for inorganic particles: phase diagram and thermal properties of a CuCl nanoplatelet precursor

We have recently reported (Angew. Chem. Int. Ed. 2004, 43 (40), 5380) the formation of CuCl nanoplatelets from an ionic liquid crystal precursor (ILCP) consisting of a 50/50 (wt/wt) mixture of bis(dodecylpyridinium) tetrachlorocuprate 1 and 6-O-palmitoyl ascorbic acid 2. Here we present the full ILCP phase diagram and the thermal behavior from a mixing ratio of 1/0 (i.e., pure 1) to 0/1 (i.e., pure 2). The ILCP exhibits a crystalline-smectic-isotropic phase transition at all mixing ratios, and the liquid crystal region is up to 90 degrees C wide. DSC shows a broad exothermic peak between ca. 70 and 170 degrees C, which is associated with the thermally induced CuCl formation. The reaction enthalpies reach -150 kJ/mol at around 50/50 (wt/wt) mixtures of the two components, and the activation energy for CuCl formation is ca. 190 kJ/mol. Thermogravimetric analysis shows that the samples degrade above ca. 200 degrees C.