Elena Bogdan

Synthesis and Structure of New 3,3,9,9-Tetrasubstituted- 2,4,8,10-Tetraoxaspiro(5.5)undecane Derivatives

The configurational and conformational behavior of some new 3,3,9,9-tetra-substituted-2,4,8,10-tetraoxaspiro[5.5]undecane derivatives with axial chirality was investigated by conformational analysis and variable temperature NMR experiments.

Synthesis and structure of new 3,7,10-substituted-phenothiazine derivatives

The synthesis of new 3,7-dibromophenothiazine derivatives bearing bromoalkyl, mercaptoalkyl and alkylthioacetate groups on the N atom at position 10 is reported. The Suzuki coupling reaction of one of these derivatives via the bromine atoms at positions 3 and 7 with bromothiophene derivatives is also discussed.

New [4.4]cyclophanes: molecular parallelograms, triangles, rhombuses, pentagons, and supramolecular constructions.

The fair or good yield synthesis of new [(4.4)(n)]cyclophanes (n = 1-5), starting from 1,4-bis(2-hydroxymethyl-5,5-dimethyl-1,3-dioxan-2-yl)benzene and several diacid-dichlorides, based on monomer and oligomer formation reactions (from 1 + 1 to 5 + 5), is reported. The structure and the complex architectures of the lattices for these cyclophanes are revealed by the X-ray molecular structure for five compounds, NMR investigations, and mass spectrometry measurements. Intramolecular and intermolecular CH-pi, p-pi, and pi-pi interactions are observed, both in solid state and solution.

Geometric enantiomerism in cyclic compounds: chiral dibrominated 1,3-dioxanes.

The first geometric enantiomers in the cyclic compounds series are reported. The investigated compounds are 2,2-disubstituted-5-methyl-1,3-dioxane derivatives in which the substituents at position 2 bear chiral centers with identical substituents but with opposite configurations. The structure of the unlike isomers was determined from the solid state molecular structure of the compounds obtained by single crystal X-ray diffractometry and the enantiomers of these diastereoisomers were observed by chiral column HPLC base-line separation. The investigated compounds were obtained by a diastereoselective bromination reaction of the corresponding 2,2-dialkyl and 2,2-dibenzyl-5-methyl-1,3-dioxanes.

A Study of Intramolecular Hydrogen Bonding in Levoglucosan Derivatives

Organofluorine is a weak hydrogen-bond (HB) acceptor. Bernet et al. have demonstrated its capability to perturb OH···O intramolecular hydrogen bonds (IMHBs), using conformationally rigid carbohydrate scaffolds including levoglucosan derivatives. These investigations are supplemented here by experimental and theoretical studies involving six new levoglucosan derivatives, and complement the findings of Bernet et al. However, it is shown that conformational analysis is instrumental in interpreting the experimental data, due to the occurrence of non-intramolecular hydrogen-bonded populations which, although minor, cannot be neglected and appears surprisingly significant. The DFT conformational analysis, together with the computation of NMR parameters (coupling constants and chemical shifts) and wavefunction analyses (AIM, NBO), provides a full picture. Thus, for all compounds, the most stabilized structures show the OH groups in a conformation allowing IMHB with O5 and O6, when possible. Furthermore, the combined approach points out the occurrence of various IMHBs and the effect of the chemical modulations on their features. Thus, two-center or three-center IMHB interactions are observed in these compounds, depending on the presence or absence of additional HB acceptors, such as methoxy or fluorine.

Supramolecular anion recognition by β-HCH

The formation of highly ordered supramolecular architectures via cooperative C(aliphatic)-H·anion contacts between β-HCH and various anions (Cl-, Br-, I- and HSO4-) was investigated by single crystal X-ray diffractometry, molecular modelling, ESI-MS and 1H-NMR titrations.

Synthesis, structure, electrochemical behaviour and electrochemical investigations on the assembling with pyrene of a novel C3 cryptand

The synthesis and the structure of a new cryptand with 1,3,5-triphenylbenzene caps and pyridine rings in the chains are reported. The formation of a host–guest assembly between the investigated cryptand and pyrene was predicted by molecular modelling and confirmed by the electrochemical investigations by cyclic voltammetry using graphite electrodes.

Synthesis and stereochemistry of new spiro(5.5)undecane derivatives with 1,3-dioxane, 1,3-dithiane, or 1,3-oxathiane rings

The synthesis and the structural investigations of spiro[5.5]undecane derivatives with S and O containing heterocycles, exhibiting similar [bis(1,3-oxathiane) spiranes] or different (1,3-dioxane-1,3-dithiane spiranes) heterocycles, in the spirane units are reported.

Considerations on the stereoselective synthesis of dibrominated spiro-1,3-dioxanes. Synthesis and stereochemistry of monobrominated precursors

The synthesis and stereochemistry of monobrominated spiro-1,3-dioxanes, involved as precursors in the diastereoselective synthesis of dibrominated 1,5-dioxaspiro[5.5]undecane derivatives bearing substituents in positions 7, 8 or 9, are reported. The structural aspects are investigated by means of NMR methods and by the molecular structure of two compounds established by single-crystal X-ray diffractometry. The data are used to determine the routes followed by the bromination reactions of spiro-1,3-dioxanes and the asymmetric induction involved in the stereoselectivity of the process.

Indenopyrans - synthesis and photoluminescence properties.

Summary New indeno[1,2-c]pyran-3-ones bearing different substituents at the pyran moiety were synthesized and their photophysical properties were investigated. In solution all compounds were found to be blue emitters and the trans isomers exhibited significantly higher fluorescence quantum yields (relative to 9,10-diphenylanthracene) as compared to the corresponding cis isomers. The solid-state fluorescence spectra revealed an important red shift of λmax due to intermolecular interactions in the lattice, along with an emission-band broadening, as compared to the solution fluorescence spectra.