Ion Grosu

Regioselective Orthopalladation of (Z)-2-Aryl-4-Arylidene-5(4H)-Oxazolones: Scope, Kinetico-Mechanistic, and Density Functional Theory Studies of the C–H Bond Activation

Orthopalladated complexes derived from (Z)-2-aryl-4-arylidene-5(4H)-oxazolones have been prepared by reaction of the oxazolone with palladium acetate in acidic medium. The reaction is regioselective, only the ortho C-H bond of the arylidene ring being activated, producing a six-membered ring. The scope and reaction conditions of the orthopalladation are dependent on the acidity of the solvent. In CF(3)CO(2)H a large number of oxazolones can be metalated under mild conditions. As acidity decreases a lesser number of oxazolones can be efficiently palladated and harsher conditions must be used to achieve similar yields. The C-H bond activation in acidic medium agrees with an ambiphilic mechanism, as determined from kinetic measurements at variable temperature and pressure for different oxazolones substituted at the arylidene ring. The mechanism has been confirmed by density functional theory (DFT) calculations, where the formation of the six-membered ring is shown to be favored from both a kinetic and a thermodynamic perspective. In addition, the dependence of the reaction rate on the acidity of the medium has also been accounted for via a fine-tuning between the C-H agostic precoordination and the proton abstraction reaction in the overall process occurring on coordinatively saturated [Pd(κ(N)-oxazolone)(RCO(2)H)(3)](2+).

Synthesis, structural analysis, and chiral investigations of some atropisomers with EE-tetrahalogeno-1,3-butadiene core.

The atropenantiomers of stable 1,2,3,4-tetrahalo-1,3-butadiene derivatives (where halogeno stands for bromine or iodine) were separated with use of chiral HPLC. The barriers for the enantiomerization process were determined on-line by dynamic HPLC (DHPLC) or off-line by classical kinetic measurements. In the case of the tetrachloro compound, the barrier was too low for DHPLC and its value was obtained by dynamic NMR experiments. The obtained barriers for chloro, bromo, and iodo derivatives correlate with the van der Waals radii of the halogens. The absolute configuration of the isolated enantiomers of the tetraiodo and tetrabromo compounds was assigned by comparison of the experimental and conformations averaged calculated VCD spectra. The identification of a signature band of the absolute configuration of the butadiene core, the sign and location of which are independent from the different conformations and substituents, allowing the safe assignment of the absolute configuration of the enantiomers of chiral 1,3-butadienes, is also reported.

Axial and helical chirality of some spiro-1,3-dioxanes

The diastereoisomerism of some spiro 1,3-dioxanes with axial chirality and of some trispiro derivatives exhibiting an axial and a hitherto unreported helical chirality for spiranic compounds is discussed.

Small Molecular Donors for Organic Solar Cells Obtained by Simple and Clean Synthesis

A small donor-acceptor molecule is synthesized in a two-step procedure involving reaction of N,N-diphenylhydrazine on 2,5-diformylthiophene and Knoevenagel condensation. Results of UV/Vis absorption spectroscopy and cyclic voltammetry show that replacement of the phenyl ring bridge of a reference compound 2 by an azo group produces a slight red-shift of λmax, an enhancement of the molecular absorption coefficient, and a decrease of the energy level of the frontier orbitals. A preliminary evaluation of the potentialities of compound 1 as donor material in a basic bilayer planar heterojunction cell of 28 mm(2) active area using C60 as acceptor gave a short-circuit current density of 6.32 mA cm(-2) and a power conversion efficiency of 2.07 %.

Simple and Versatile Molecular Donors for Organic Photovoltaics Prepared by Metal-Free Synthesis

Donor-acceptor molecules (D-π-A) built by connecting a diphenylhydrazone block to a dicyanovinyl acceptor group via various thiophene-based π-conjugating spacers (1-5) were synthesized from mono- or dialdehydes by a simple metal-free procedure. Cyclic voltammetry and UV/Vis absorption spectroscopy show that the extension and/or increase of the donor strength of the spacer produces a decrease of the HOMO and LUMO energy level, a red shift of the absorption spectrum and an increase of the molecular absorption coefficient. Compared to solutions, the optical spectra of spin-cast thin films of compounds 1-3 show a broadening and red shift of the absorption bands, consistent with the formation of J-aggregates. In contrast the blue shift observed for the EDOT-containing compounds 4 and 5 suggests the presence of H-aggregates. Solution-cast and vacuum-deposited films of donors 1-5 were evaluated in solar cells with fullerene C60 as acceptor. A power-conversion efficiency among the highest reported for bilayer devices of basic configuration was obtained with compound 2. On the other hand, the results obtained with 4 and 5 suggest that the presence of EDOT in the structure can have deleterious effects on the organization and performances of the donor material.

Unexpected [2 + 2] C–C bond coupling due to photocycloaddition on orthopalladated (Z)-2-aryl-4-arylidene-5(4H)-oxazolones

A [2 + 2] photocycloaddition has been observed in regioselectively orthopalladated 2-aryl-4-arylidene-5(4H)-oxazolones, leading to unprecedented cyclobutane-bis(oxazolones).

Replacement of the 4'-hydroxy group of amodiaquine and amopyroquine by aromatic and aliphatic substituents: synthesis and antimalarial activity.

4′‐Substituted analogues of amodiaquine and amopyroquine were synthesized using Csp2–Csp2 and Csp2–Csp3 Suzuki–Miyaura cross‐coupling reactions as the key step. The new derivatives were found to be active against both chloroquine (CQ)‐sensitive and CQ‐resistant strains of P. falciparum, with IC50 values in the range of 7–200 nM; one compound showed in vivo activity.

Synthesis and stereochemistry of some dispiro-1,3-dioxanes with axial and helical chirality

Abstract The stereoisomerism of some dispiro-1,3-dioxanes is discussed in terms of conformational analysis and axial and helical chirality. The influence of the flexibility of the rings on the representative number of isomers and on their NMR spectra is commented. For the 3,12-disubstituted-1,5,10,14-teraoxadispiro[5.2.5.2]hexadecane derivatives displaying a semiflexible structure two configurational diastereomers named “6,9-dispiro-syn” and “6,9-dispiro-anti” were identified. The ratio between these isomers was determined by the diastereotopicity of protons and carbon atoms.

Conformational analysis of some spiro and polyspiro 1,3-dioxane compounds with axial and helical chirality

Some spire and trispiro 1,3-dioxane compounds are discussed in terms of their axial and the helical chirality (all rings are six-membered). The influence of conformation on the number of isomers and on their interrelationship has been followed by means of high resolution and dynamic NMR experiments using the diastereotopicity of the proton and carbon atoms. Interconversions between configurational isomers (presenting three chiral elements) without the breaking of bonds are reported.

Study on the atropisomerism of some new 2-aryl-1,3-dioxanes

Abstract The synthesis and the stereochemistry of a new class of compounds showing atropisomerism, the 1,3-dioxane derivatives bearing disymmetric axial aryl groups in position 2 of the 1,3-dioxane ring are reported.