Benzyne-induced ring opening reaction of thiiranes. Efficient synthesis of phenyl vinyl sulfides

A series of thiiranes react with benzyne to provide an efficient synthesis of phenyl vinyl sulfides. The reaction is stereospecific, thus producing cis-(phenylthio)-stilbene from cis-2,3-diphenylthiirane and trans-(phenylthio)stilbene from trans-2,3-diphenylthiirane.     

Synthesis of polyfunctionalized furans from 3-acetyl-1-aryl-2-pentene-1,4-diones

The BF₃-catalyzed cyclization of 3-acetyl-1-aryl-2-pentene-1,4-diones 1a-e in the presence of water in boiling tetrahydrofuran gave bis(3-acetyl-5-aryl-2-furyl)methanes 2a-e in 26-79% yields along with a small amount of 3-acetyl-5-aryl-2-methylfurans 3a-e. The exact structure of 2a was determined by X-ray crystallography. The use of a half volume of the solvent for the reaction of 1a resulted in the formation of 2,4-bis(3-acetyl-5-phenyl-2-furfuryl)-3-acetyl-5-phenylfuran (4) together with 2a and 3a. A similar reaction of 1a was carried out in the presence of 3-acetyl-5-(4-methylphenyl)-2-methylfuran (3d) to afford 4-(3-acetyl-5-phenyl-2-furfuryl)-3-acetyl-5-(4-methylphenyl)-2-methylfuran (5) in 49% yield. The BF₃-catalyzed reaction of 1a with 2,4-pentanedione in dry tetrahydrofuran at 23°C gave 3-(3-acetyl-5-phenyl-2-furfuryl)-4-hydroxy-3-penten-2-one (6a) and 3-(3-acetyl-2-methyl-4-phenyl-5-furyl)-4-hydroxy-3-penten-2-one (7a) in 66 and 24% yields, respectively. The product distribution depended on the reaction temperature. A similar reaction of 1b-e also yielded the corresponding trisubstituted furans 6b-e and tetrasubstituted furans 7b-e in good yields. These results suggested the presence of the furfuryl carbocation intermediate A during the reaction. The one-pot synthesis of 6a and 7a was also achieved by a similar reaction using phenylglyoxal. The deoxygenation of 1a with triphenylphosphine gave 3a in 88% yield, while 1a was treated with concentrated hydrochloric acid to yield 3-acetyl-2-chloromethyl-5-phenylfuran (8) which was quantitatively transformed in ethanol into 3-acetyl-2-ethoxymethyl-5-phenylfuran (9) and in water into 3-acetyl-5-phenylfurfuryl alcohol (10), respectively. In addition, the Diels-Alder reaction of cyclopantadiene with 1a gave the corresponding [4+2] cycloaddition products 11 and 12.     

Penning ionization electron spectroscopy of C6H6 by collision with He*(2 3 S) metastable atoms and classical trajectory calculations: optimization of ab initio model potentials

The potential energy surface of benzene (C(6)H(6)) with a He*(2(3)S) atom was obtained by comparison of experimental data in collision-energy-resolved two-dimensional Penning ionization electron spectroscopy with classical trajectory calculations. The ab initio model interaction potentials for C(6)H(6)+He*(2(3)S) were successfully optimized by the overlap expansion method; the model potentials were effectively modified by correction terms proportional to the overlap integrals between orbitals of the interacting system, C(6)H(6) and He*(2(3)S). Classical trajectory calculations with optimized potentials gave excellent agreement with the observed collision-energy dependence of partial ionization cross sections. Important contributions to corrections were found to be due to interactions between unoccupied molecular orbitals and the He*2s orbital. A C(6)H(6) molecule attracts a He*(2(3)S) atom widely at the region where pi electrons distribute, and the interaction of -80 meV (ca. -1.8 kcal/mol) just cover the carbon hexagon. The binding energy of a C(6)H(6) molecule and a He* atom was 107 meV at a distance of 2.40 A on the sixfold axis from the center of a C(6)H(6) molecule, which is similar to that of C(6)H(6)+Li and is much larger than those of the C(6)H(6)+[He,Ne,Ar] systems.     

Synthesis and Photocatalytic Property of Hectorite/(Pt,TiO2) and H4Nb6O17/(Pt,TiO2) Nanocomposites

Abstract

TiO₂ and Pt have been intercalated in hectorite and H₄Nb₆O₁₇. The height of TiO₂ and Pt pillars was less than 0.8 nm and the band gap energy of TiO₂ pillars was ca. 3.3 eV. Both hectorite/TiO₂ and H₄Nb₆O₁₇(Pt, TiO₂) were capable of hydrogen evolution following irradiation from a high pressure mercury are (λ > 290 nm) in the presence of methanol as a sacrificial hole acceptor and the hydrogen evolution was enhanced by co-incorporation of Pt, although hectorite and hectorite/Pt did not show photocatalytic activity. Incorporation of Pt or Pt and TiO₂ in the interlayer of H₄Nb₆O₁₇ has resulted in enhanced photo evolution of hydrogen, however, TiO₂ alone in the interlayer of H₄Nb₆O₁₇ showed adverse photocatalytic activity.     

Application of Polymer-Embedded Tris(2,2′ Bipyridine-Ruthenium(II) to Photodetection of Oxygen

A Nafion film containing tris(2,2′-bipyridine)ruthenium(II) as a luminescence probe was applied to photodetection of oxygen in a gas by utilizing the luminescence quenching by dioxygen. The linear Stern-Volmer plots of the emission intensity with respect to the oxygen concentration allowed quantitative determination of the oxygen. From the emission decay studied by a single-photon counting method, it was concluded that the quenching of the excited state Ru complex by oxygen proceeds by a conventional dynamic mechanism.     

Low‐Symmetry Ω‐Shaped Zinc Phthalocyanine Sensitizers with Panchromatic Light‐Harvesting Properties for Dye‐Sensitized Solar Cells

Two low‐symmetry phthalocyanines (Pcs) substituted with thiophene units at the non‐peripheral (α) and peripheral (β) positions were synthesized and their optical, electronic‐structure, and electrochemical properties were investigated. The substitution of thiophene units at the α positions of the phthalocyanine skeleton resulted in a red shift of the Q band and significantly modified the molecular‐orbital electronic distributions just below the HOMO and just above the LUMO, with distortion of the typical Gouterman four‐orbital arrangement of MOs. Two amphiphilic Ω‐shaped ZnPcs ( αPcS1 and αPcS2 ) bearing a π‐conjugated side chain with an adsorption site at an α position of the Pc macrocycle were synthesized as sensitizers for dye‐sensitized solar cells (DSSCs). The absorption spectra of αPcS1 and αPcS2 showed red shifted Q bands and a broad band from 350 to 550 nm assignable to the intramolecular charge‐transfer transition from the ZnPc core to the side chains. Time‐dependent DFT calculations provided a clear interpretation of the effect of the thiophene conjugation on the typical phthalocyanine core π MOs. Compound αPcS1 was used as a light‐harvesting dye on a TiO₂ electrode for a DSSC, which showed a panchromatic response in the range 400–800 nm with a power conversion efficiency of 5.5 % under one‐sun conditions.     

Generation of ynolates via reductive lithiation using flow microreactors

A new method has been developed for the generation and subsequent reaction of ynolates in a micro flow reactor system. This new procedure allowed for ynolates to be prepared at 0 °C or ambient temperature within 1 min via a reductive lithiation reaction, whereas the corresponding batch processes generally require low temperature control and extended reaction times of up to 1 h. The resulting ynolates were applied to the olefination of carbonyl compounds, with the reactions reaching completion in a much shorter reaction time in the continuous flow reactor than the batch reactor. These results highlight the practical utility of the ynolate reaction, and represent the first reported example of the use of lithium naphthalenide in a flow microreactor, which would contribute to progress of the flash chemistry.