An alternative approach to 3-(diphenylphosphino)hexahelicene

3-(Diphenylphosphino)hexahelicene is synthesised in good yield and purity, via a three-step sequence involving a palladium-catalysed Mizoroki-Heck coupling reaction and classical oxidative photocyclisation. Mononuclear ruthenium and palladium complexes of 3-(diphenylphosphino)hexahelicene are prepared and characterised.     

Synthesis and characterization of new hexahelicene derivatives

The synthesis and structural characterization of a new hexahelicene derivative 2 is reported. This compound features a new type of structure bearing a bromine atom and a methoxy group. Suitable crystals of the latter indicate that its conformation closely resembles that of the unsubstituted [6]helicene, whose idealized symmetry is C2. This 3-bromo-14-methoxyhexahelicene was subjected to lithiation/phosphinilation and yielded the new 3-methoxy-14-(diphenylphosphino)hexahelicene 3.     

Synthesis of a new N-containing hexahelicene

A new helically chiral hexacyclic system, containing one pyridine unit, was prepared through a four-step synthesis involving palladium promoted Mizoroki-Heck couplings and classical oxidative photodehydrocyclisation.     

Synthesis of novel azonia Helicenes containing terminal thiophene rings

The Knoevenagel condensation of the 9‐methyl derivatives of thieno[3,2‐a]‐ and thieno[2,3‐a]‐quinolizinium salts ( 2b and 3b ) with appropriate arylaldehydes yielded 9‐(arylvinyl)thieno[3,2‐a]‐ and 9‐(arylvinyl)thieno[2,3‐a]quinolizinium salts ( 4a‐c and 5a‐c ), respectively, which underwent photocyclization to give a series of novel hetero[5]helicenes ( 6a,b and 7a‐d ) containing quinolizinium and thiophene rings.     

A new approach to polycyclic azonia cations by ring-closing metathesis

The ring-closing metathesis (RCM) reaction of N-vinyl-alpha-(2-styryl)azinium salts, using the Hoveyda-Grubbs catalyst, leads to different tricyclic and tetracyclic azonia cations with moderate to good yields. This is the first time that a highly electron-deficient alkene such as an N-vinylpyridinium has been involved in an RCM process.     

First synthesis of biquinoliziniun salts: novel example of a chiral azonia dication

[Structure: see text] The 1,1'-, 2,2'-, and 3,3'-biquinolizinium dications are described for the first time and were prepared using palladium-catalyzed homocoupling reactions of the corresponding isomeric bromoquinolizinium bromides. Theoretical calculations show 1,1'- and 4,4'-biquinolizinium dications to be chiral molecules, the latter of which has a high energy of formation, a factor that probably precludes its formation.     

An unusual synthesis of a spirothioxanthene derivative

The reaction of diphenyl sulfone with 2,3-dibromophthalazine-1,4-dione in the presence of n-butyllithium gave a spiro-9H-thioxanthene-10,10-dioxide derivative in 45% yield, the structure of which was proved by X-ray crystallography.     

Vibrational Raman optical activity of pi-conjugated helical systems: hexahelicene and heterohelicenes

Helicenes constitute a special class of molecules combining helical conformation with pi-electron delocalization. These confer to helicenes specific chirooptical properties. In this article, we investigate the vibrational signatures thanks to the simulation of vibrational Raman optical activity (VROA) spectra. For that, four representative helicenes: hexahelicene, tetrathia-[7]-helicene, and its pyrrole and furan analogs have been simulated and interpreted using a recently implemented analytical scheme. Helicenes show intense VROA peaks attributed to their pi-conjugated structure and associated with collective vibrational modes. In hexahelicene, the dominant VROA features are due to vibrational modes involving motions of the carbon skeleton and H-wagging, but the intensity finds its source almost exclusively in the former. In the case of the three heterohelicenes, the previous statement is also verified, and on changing the heteroatoms, similar modes presenting comparable atomic contribution patterns have been highlighted, though the vibrational and electronic properties are modified. Some fingerprints could therefore be associated with the helicity of the system. In particular, in forward spectra, most of the VROA bands are positive for left-handed helicenes. Nevertheless, the spectral patterns are quite complex, and no easy rule-of-thumb could distinguish between the different heterohelicenes. Then, considering the fact that most of the contributions originate from the C atoms (group coupling matrices decomposition), it can be concluded that the major role of the heteroatom is restricted to modifying the geometry and the normal modes. At last, the small impact of the gauge-origin on the calculated spectra using a relatively modest basis set (rDPS:3-21G) is demonstrated here in the case of the tetrathia-[7]-helicene molecule presenting a C(2) symmetry. This further demonstrates the adequacy of this basis set for VROA calculations.     

An antibacterial biphenyl derivative from Garcinia bancana MIQ

From the methanol extract of the twigs and leaves of Garcinia bancana MIQ., one new biphenyl derivative (1), was isolated and characterized along with nine known compounds; garcinol, isogarcinol, (-)-mellein, 8-hydroxy-6-methoxy-3-n-pentylisocoumarin, blumenol C O-beta-D-glucoside, quercetin 3-O-alpha-L-rhamnoside, kaemferol 3-O-alpha-L-rhamnoside, lupeol and stigmasterol. Their structures were determined by analysis of 1D and 2D NMR data and comparison of spectral data and physical data with those previously reported. The antibacterial activity against methicillin-resistant Staphylococcus aureus was evaluated. Garcinol showed the lowest minimum inhibition concentration (MIC) at 16 microg/ml while compound 1 exhibited weaker activity with MIC value of 64 microg/ml.     

An enantioselective synthesis of a MEM-protected aetheramide A derivative

Aetheramides A and B are very potent anti-HIV agents. An enantioselective synthesis of a MEM-protected aetheramide A derivative is described. The synthesis was accomplished in a convergent and stereoselective manner. The key reactions involved asymmetric dihydroxylation, asymmetric allylation, asymmetric syn-aldol reactions, and asymmetric hydrogenation.     

An unusual picoline derivative from the trifluoroacetolysis of thiostrepton

Trifluoroacetolysis of thiostrepton followed by treatment with methanol and aqueous sodium hydroxide led to the formation of N‐(2‐picolinoyl)serine methyl ester, the first pyridine‐containing compound isolated from the chemical degradation of thiostrepton.     

An analytical derivative procedure for the calculation of vibrational Raman optical activity spectra

We present an analytical time-dependent Hartree-Fock algorithm for the calculation of the derivatives of the electric dipole-magnetic dipole polarizability with respect to atomic Cartesian coordinates. Combined with analogous procedures to determine the derivatives of the electric dipole-electric dipole and electric dipole-electric quadrupole polarizabilities, it enables a fully analytical evaluation of the three frequency-dependent vibrational Raman optical activity (VROA) invariants within the harmonic approximation. The procedure employs traditional non-London atomic orbitals, and the gauge-origin dependence of the VROA intensities has, therefore, been assessed for the commonly used aug-cc-pVDZ and rDPS:3-21G basis sets.     

An unusual equilibrium between a cyclopropylcarbonyl compound and a 2,3-dihydrofurane derivative

The equilibrium data of the thermal interconversion between a cyclopropylcarbonyl derivative with trispiro structure and a dihydrofuro[2,3-c]pyrazole have been examined.     

An explicit linear six-step method with vanished phase-lag and its first derivative

An explicit linear sixth algebraic order six-step method with vanished phase-lag and its first derivative is constructed in this paper. We will study the method theoretically and computationally. Theoretical investigation contains the building of the method, the calculation of the local truncation error, the comparative error analysis of the new method with the method with constant coefficients and the stability analysis of the new method using scalar test equation with different frequency than the frequency of the scalar test equation used for the development of the method. Computational investigation contains the application of the new obtained linear six-step method to the resonance problem of the radial time independent Schrödinger equation. The theoretical and computational study lead us to the summary that the new proposed linear scheme is computationally and theoretically more efficient than other well known methods for the numerical solution of the Schrödinger equation and related periodic initial or boundary value problems.     

An acrylated fullerene derivative for efficient and thermally stable polymer solar cells

The continuous microstructure evolution occurring in active layers of polymer-fullerene solar cells is one of the main causes for their device instability. With aim to tackle it, this work developed a new polymerizable fullerene acceptor, [6,6]-phenyl-C₆₁-butyl acrylate (PC₆₁BA). It was found that PC₆₁BA has similar light-absorption properties and HOMO and LUMO energy levels as [6,6]-phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM), and can be converted into insoluble oligomers upon heating at 150 °C. Polymer-fullerene solar cells using poly(3-hexylthiophene) (P3HT) as donor and PC₆₁BA as acceptor exhibited an optimized efficiency of 3.54%, the performance comparable to P3HT/PC₆₁BM cells (optimized efficiency: 3.70%). But, the former possess much better thermal stability than the latter owing to aggregation suppression by the polymerized PC₆₁BA. These results indicate that PC₆₁BA, unlike most previous reported, is a unique polymerizable fullerene derivative that can be used alone as acceptor to achieve both efficient and thermally stable polymer solar cells.     

Conformational studies on helicenes—IX1: A hexahelicene containing an aromatic,carbocyclic, five-membered ring

The reaction of phenathro[3,4-c]fluorene (1) with lithium in tetrahydrofuran (THF) or hexamethylphosphoric triamide (HMPT) leads to the fully aromatic phenanthro[3,4-c]fluorenyl anion (2). The influence of the ring current of the five-membered ring and the negative charge on the proton chemical shifts has been analyzed. The low-field position of the A-portion (H(16)) is ascribed to the nearby position of the Li-cation. Even in HMPT the Li^?+2^? salt appears to be present as a contact ion pair.     

An electroactive nickel containing polymeric film obtained by electrochemical reduction of an aryl-nickel derivative

The electrochemical reduction of [Ni(PPh₃)₂(p-C₆H₄Br)Br] in acetonitrile results in a polymeric coating of a nickel-containing poly-p-phenylene, formulated as [-Ni(p-C₆H₄)_n-] (n=6?7) on the basis of elemental analysis, IR, UV, MS and ESCA measurements. This coating is found to undergo a two-electron reversible reduction and a one-electron reversible oxidation with a large potential window (3.6 V), without the polymeric film being destroyed. Moreover, the polymer obtained is shown to be electroactive towards dissolved reactants via permeation or mediated electron transfer, depending on the molecular size of the electroactive species employed.