Obtaining new flavanones exhibiting antifungal activities by methyltrioxorhenium-catalyzed epoxidation-methanolysis of flavones

New 3-hydroxy-2-methoxyflavanones have been obtained through epoxidation-methanolysis of the corresponding flavone with urea-hydrogen peroxide (UHP)/methyltrioxorhenium (CH₃ReO₃, MTO) catalytic system in methanol as nucleophilic solvent. After acetylation of the reaction mixtures, the corresponding cis- and trans-3-acetoxy-2-methoxyflavanones have been isolated and characterized by spectroscopic analyses. Their antifungal activity has been tested in vitro against three fungal strains of common saprotrophic soil and seed fungi, such as Trichoderma koningii, Fusarium solani and Cladosporium herbarum, potentially pathogenic for humans. Some aspects of the structure-activity relationship of the most active compounds have been evaluated. The mycelial growth of T. koningii and C. herbarum has been totally inhibited from cis-3-acetoxy-2,6-dimethoxyflavanone 7c and cis-3-acetoxy-2,7-dimethoxyflavanone 13c at the lowest concentration (0.5×10⁻⁴ M).     

2-Arylhydroxytyrosol derivatives via Suzuki-Miyaura cross-coupling

2-Arylhydroxytyrosol derivatives, a new class of hydroxytyrosol derivatives, have been prepared in high to excellent yields from the corresponding 2-chloro precursors via Suzuki-Miyaura cross-coupling with arylboronic acids containing electron-donating, electron-withdrawing, as well as ortho substituents. A remarkable halide effect has been observed. 2-Iodo- and 2-bromohydroxytyrosol derivatives have been found to be ineffective cross-coupling partners in many cases. The acetonide and carbonate protecting groups can be readily removed.     

Palladium-catalyzed hydroarylation of alkynes with arenediazonium salts

The palladium-catalyzed hydroarylation of arenediazonium tetrafluoroborates with alkynes in the presence of triphenylsilane affords stereoselectively hydroarylation products in moderate to high yields. The reaction tolerates a variety of substituents including keto, ester, cyano, and nitro groups and can be performed as a one-pot procedure generating the arenediazonium salt in situ. With ethyl phenylpropynoate as the starting alkyne, the hydroarylation affords ethyl (Z)-2-arylcinnamates stereo- and regioselectively.     

Synthesis, reactivity, electrochemical behavior, and crystal structure of a family of multivalent metal carbido-carbonyl clusters based on the rh(10)(c)(2)au(4-6) framework

Six metal carbido-carbonyl clusters have been isolated and recognized as members of a multivalent family based on the dioctahedral Rh(10)(C)(2) frame, with variable numbers of CO ligands, AuPPh(3) moieties, and anionic charge: [Rh(10)(C)(2)(CO)(x)(AuPPh(3))(y)](n-) (x = 18, 20; y = 4, 5, 6; n = 0, 1, 2). Anions [Rh(10)(C)(2)(CO)(18)(AuPPh(3))(4)](-) ([2](-)) and [Rh(10)(C)(2)(CO)(18)(AuPPh(3))(4)](2-) ([2](2-)) have been obtained by the reduction of [Rh(10)(C)(2)(CO)(18)(AuPPh(3))(4)] (2) under N(2), while [Rh(10)(C)(2)(CO)(18)(AuPPh(3))(5)](-) ([3](-)) was obtained from [Rh(10)(C)(2)(CO)(20)(AuPPh(3))(4)] (1) by reduction under a CO atmosphere. [3](-) can be better obtained by the addition of AuPPh(3)Cl to [2](2-). [Rh(10)(C)(2)(CO)(18)(AuPPh(3))(6)] (4) is obtained from [3](-) and 2 as well by the reduction and subsequent addition of AuPPh(3)Cl. The molecular structures of [2](2-) ([NBu(4)](+) salt), [3](-) ([NMe(4)](+) salt), and 4 have been determined by single-crystal X-ray diffraction. The redox activities of complexes 1, 2 and [3](-) have been investigated by electrochemical and electron paramagnetic resonance (EPR) techniques. The data from EPR spectroscopy have been accounted for by theoretical calculations.     

Regiochemical control of the ring opening of 1,2-Epoxides by means of chelating processes. 11. Ring opening reactions of aliphatic mono- and difunctionalized cis and trans 2,3- and 3,4-Epoxy Esters

The regiochemical outcome of the ring opening of 1,2-epoxides through chelation processes assisted by metal ions, was verified in the azidolysis of simple aliphatic cis and trans 2,3- and 3,4-epoxy esters and in the corresponding derivatives bearing an ether functionality (OBn) in an allylic relationship to the oxirane ring. The results indicate that the behavior of these epoxides is influenced both by the opening conditions (standard or metal-assisted) and the promoting metal salt [LiClO₄ or Mg(ClO₄)₂].     

Dimethyl carbonate: an environmentally friendly solvent for hydrogen peroxide (H2O2)/methyltrioxorhenium (CH3ReO3, MTO) catalytic oxidations

Environmentally friendly oxidations of various organic compounds with the hydrogen peroxide (H₂O₂)/methyltrioxorhenium (CH₃ReO₃, MTO) catalytic system have been described in dimethyl carbonate (DMC), a cheap commercially available and benign chemical having interesting solvating properties, low toxicity and high biodegradability. Oxidations proceeded with good conversions and in good yields. Spectrophotometric analysis demonstrated that the [CH₃ReO(O-O)₂] complex was formed in DMC and that it was stable for several days at room temperature.     

Core electron transitions as a probe for molecular chirality: natural circular dichroism at the carbon K-edge of methyloxirane

We have measured for the first time the X-ray natural circular dichroism (XNCD) of a chiral molecule in an isotropic medium. In this condition the only surviving term contributing to CD is the cross product between the electric dipole and the magnetic dipole transition moments. The non-zero value of the magnetic dipole transition moment in a 1s-to-valence electron transition is attributed to contribution of valence states to core molecular orbitals. These results open the way to a "local" chiral molecular analysis and to the study of stereochemically selected photochemical processes.     

Epoxidation of chromones and flavonoids in ionic liquids

A convenient and efficient procedure for the epoxidation of chromone, isoflavone, and chalcone derivatives using 1-butyl-3-methyl imidazolium tetrafluoroborate [bmim]BF₄ as solvent and alkaline hydrogen peroxide as oxidant is described. All reactions proceed in good yields and faster than in conventional solvents. No evidence of formation of compounds derived from the opening of the epoxide ring was attained.     

Ferrocenyl-functionalised terpyridines and their transition-metal complexes: syntheses,structures and spectroscopic and electrochemical properties

Terpyridine ligands of the type Fc'-X-tpy (Fc'=ferrocenyl or octamethylferrocenyl, X=rigid spacer, tpy'=4'-substituted 2,2':6',2'-terpyridine) were prepared, crystallographically characterised and used for the synthesis of di- and trinuclear bis(terpyridine) complexes of RuII, FeII and ZnII. Donor-sensitiser dyads and triads based on RuII were thoroughly investigated by (spectro)electrochemistry, UV/Vis, transient absorption and luminescence spectroscopy, and an energy level scheme was derived on the basis of the data collected. Intramolecular quenching of the photoexcited RuII complexes by the redox-active Fc' groups can occur reductively and by energy transfer. Both the redox potential of the donor Fc' and the nature of the spacer X have a decisive influence on excited-state lifetimes and emission properties of the complexes. Some of the compounds show room-temperature luminescence, which is unprecedented for ferrocenyl-functionalised compounds of this kind.