Band structure of even and ions of odd polyenes

The analysis of experimental data for singlet transitions (E _n) of even polyenes (I), cations (II) and anions (III) of odd polyenes show that for infinite chains E (I)/E (II)=E (I)/E (III) = 2:1. It is shown that the energy gap is equal for the three systems. In cases (II) and (III) there is a level (NBMO) in the gap which is vacant in (II) and occupied in (III). That is why the first optical transition in (II) and (III) depends on the semiwidth of the gap.     

Thermal electrocyclization reactions II: benzooctatetraenes and benzodecapentaenes

Thermal electrocyclization reactions of benzooctatetraenes and benzodecapentaenes substituted with R=H, Cl, and methyl were studied experimentally and computationally. Methyl and unsubstituted benzooctatetraenes and benzodecapentaenes give the [4.2.0]bicyclooctadiene products by 8π,6π-electrocyclization. Chlorine substitution led to thermal rearrangement of the initially formed 8π,6π-electrocyclization intermediates to give unprecedented products.     

Synthesis, characterization and optical response of polyene-cored stilbenoid dendrimers

The synthesis of first- and second-generation dendrimers bearing phenylenevinylene chromophores within the dendritic branches (stilbenoid dendrimers) and polyenes (3 and 5 double bonds) as cores is described. A preliminary study of the optical properties of the resulting compounds was conducted by UV/vis and fluorescence spectroscopy.     

A comprehensive survey of stille-type Csp-Csp single bond forming processes in the synthesis of retinoic acid and analogs

The synthesis of the retinoid skeleton has been exhaustively explored using the Stille coupling for the formation of the side-chain single bonds. On employing the experimental catalytic conditions developed by Farina [Pd₂(dba)₃, AsPh₃, NMP] we have modified the electronic and steric requirement of the coupling parters, alkenyl stannanes and electrophiles (alkenyl iodides and triflates). The comprehensive survey afforded appropriately matched components for every bond formation considered. Moreover, from the comparison of the reactivities of different coupling partners with different degrees of steric hindrance, the sensitivity of the Stille coupling to steric effects was confirmed. Besides providing a variety of building blocks for retinoid synthesis, the study highlights some trends that might be useful for the application of the Stille reaction to the synthesis of unsubstituted conjugated polyenes.     

Polycephalin B and C: Unusual Tetramic Acids from Plasmodia of the Slime Mold Physarum polycephalum (Myxomycetes)

Illumination results in increased formation of metabolites 1 and 2 in the plasmodia of the slime mold Physarum polycephalum. This was determined from HPLC studies undertaken in the search for the photoactive substances involved in the “blue-light phenomenon”. The isolation and structure elucidation of 1 and 2 is described.     

An application of RPA theory to conjugated systems in the excited states

In order to obtain a relationship between the molecular dimension and the correlation effect, RPA method has been applied to the calculation of electronic transition energies of linear polyenes. It has been found that the effect of electron correlation on the excitation energy decreases with increasing the size of molecule. The calculated oscillator strengths are remarkably improved by RPA calculation.     

Preparation of E-(1,2-difluoro-1,2-ethenediyl)bis(tributylstannane)

Chlorotrifluoroethene is converted in situ to [F₂CCFSiMe₃]. The crude [F₂CCFSiMe₃] solution is reduced with lithium aluminum hydride to (HFCCFSiMe₃), which (without isolation) is converted to (Z)-HFCCFSnBu₃. Subsequent metallation and trapping of the vinyllithium reagent with Bu₃SnCl gives (E)-Bu₃SnCFCFSnBu₃ in 73% overall yield. Only two isolation steps are required and the use of Me₃SiCl and F₂CCFCl provides a cheap, economical route to this useful synthon.     

Calculations of molecular polarizabilities using the Valence Effective Hamiltonian (VEH) method

In this paper, we investigate the applicability of the Valence Effective Hamiltonian (VEH) method to calculations of theoretical molecular linear polarizabilities by the Sum-Over-States (SOS) methodology. Test calculations are presented on the polyene series. They indicate that the method gives qualitatively the same trends asab initio small basis sets calculations.Dedicated to Professor J. Koutecký on the occasion of his 65th birthday     

Standardless spectrochemical analysis and direct simulations of time-resolved vibronic spectra of polyatomic molecules, isomers and mixtures

The efficient method for calculation of dynamical time-resolved vibronic spectra of polyatomic molecules is proposed. It allows to perform direct real-time computer simulations of such spectra for models of complex compounds, isomers and multicomponent mixtures with quantum beats and non-radiative vibrational relaxation taken into account. The examples of calculated spectra show the ways of how to search and select optimal experimental conditions and retrieve the most informative data for solution of inverse spectral problems in different situations. The new method of standardless analysis based on time-resolved vibronic spectroscopy has been developed and its main ideas are presented here. This method is able to solve quantitative and qualitative spectrochemical problems for individual substances and multicomponent mixtures (even for species with similar optical properties) with the use of experimentally measured relative intensities of dynamical spectra only. The algorithms of how to perform analysis in various experimental conditions are proposed.     

Total synthesis of a dienynone from Echinacea pallida

The first total synthesis of (8Z,13Z)-pentadeca-8,13-dien-11-yn-2-one is described. This dienynone was recently isolated from the n-hexane extract of Echinacea pallida roots and displayed a selective cytotoxic activity toward cancer cells, thus featuring as a potential anticancer lead. The product was obtained in 11 steps in 25% overall yield.