Visible-light-mediated addition of α-aminoalkyl radicals generated from α-silylamines to α,β-unsaturated carbonyl compounds

Visible-light-mediated addition of α-aminoalkyl radicals generated from α-silylamines to α,β-unsaturated carbonyl compounds using a photoredox catalyst is developed. We also succeeded in the isolation of a silyl enol ether as a primary product of the photochemical reaction.     

Prediction of the stability of modified RNA duplexes based on deformability analysis: oligoribonucleotide derivatives modified with 2'-O-cyanoethyl-5-propynyl-2-thiouridine as a promising component

We describe a method to predict the stability of a modified RNA duplex. Ten unique modified RNA duplexes showed a linear relationship between the calculated and experimentally determined duplex stabilities.     

Enantioselective alkylation of β-keto phosphonates by direct use of diaryl methanols as electrophiles

Enantioselective alkylation of β-keto phosphonates with diaryl methanols in the presence of catalytic amounts of copper(ii) trifluoromethanesulfonate and an optically active ligand gives the corresponding alkylated products in good to high yields with a high enantioselectivity.     

Isolation and characterization of phenolic antioxidants from Plantago herb

Seven phenolic compounds, including a new phenylethanoid glycoside, were isolated from the ethyl acetate fraction of an aqueous ethanol extract of Plantago Herb (whole part of Plantago asiatica L.), which showed significant antioxidative activity. The new compound was characterized as 2-(3,4-dihydroxyphenyl)ethyl 3-O-β-D-allopyranosyl-6-O-caffeoyl-β-D-glucopyranoside on the basis of spectral and chemical evidence, and its antioxidant activity was comparable to that of tea catechins.     

Phosphine-free palladium catalyzed Mizoroki-Heck reaction using hydrazone as a ligand

Glyoxal bishydrazones 1 and pyridyl-hydrazone 2b were prepared and examined as a ligand for the Mizoroki-Heck cross-coupling reaction of aryl halides and olefin. We found that PdCl2(MeCN)2/hydrazone ligand 1e was a phosphine-free efficient catalyst system for a variety of substrates to produce the Mizoroki-Heck coupling products in good yields.     

Palladium-catalyzed sonogashira and hiyama reactions using phosphine-free hydrazone ligands

Palladium/copper-catalyzed Sonogashira cross-coupling reaction of aryl halides with a variety of terminal alkynes under amine-free conditions in dimethylformamide (DMF) at 80 degrees C gave internal arylated alkynes using PdCl2(MeCN)2 with phosphine-free hydrazone 2a as a ligand and CuI as the cocatalyst in good yields. We also found PdCl2/hydrazone ligand 1d in PhMe at 80 degrees C was a phosphine-free efficient catalyst system for a Hiyama cross-coupling reaction of aryl bromides with aryl(trialkoxy)silanes in good yields.     

Synthesis and stability of 1,1-dialkyl-1H-azulenium cations

Starting from trimethylsilyl enol ether of 1-acetyl-1,3,5-cycloheptatriene, the title 1,1-dimethyl-, 1,1-diethyl-, and 1,1-dipropyl-1H-azulenium cations 6-8 were synthesized in five steps. The order of pK_R+ values of these cations was found to be 7>8>6. A comparison of the values between 1,1-dialkyl- and 1,1-spiroalkylated 1H-azulenium cations with the same number of carbon atoms at the 1-position provided the results of 7>1 and 8<3. The cation 8 shows a relatively lower pK_R+ value to those of 3 and 7 probably due to its slightly bulkier propyl groups from which solvation stabilization of 8 under the conditions suffers. An intermolecular charge-transfer interaction between the cations and dibenzo-24-crown-8 was also studied.     

Efficient charge injection from the S2 photoexcited state of special-pair mimic porphyrin assemblies anchored on a titanium-modified ITO anode

A novel surface fabrication methodology has been accomplished, aimed at efficient anodic photocurrent generation by a photoexcited porphyrin on an ITO (indium-tin oxide) electrode. The ITO electrode was submitted to a surface sol-gel process with titanium n-butoxide in order to deposit a titanium monolayer. Subsequently, porphyrins were assembled as monolayers on the titanium-treated ITO surface via phosphonate, isophthalate, and thiolate groups. Slipped-cofacial porphyrin dimers, the so-called artificial special pair at the photoreaction center, were organized through imidazolyl-to-zinc complementary coordination of imidazolylporphyrinatozinc(II) units, which were covalently immobilized by ring-closing olefin metathesis of allyl side chains. The modified surfaces were analyzed by means of X-ray photoelectron spectroscopy. Photoirradiation of the porphyrin dimer generated a large anodic photocurrent in aqueous electrolyte solution containing hydroquinone as an electron sacrificer, due to the small reorganization energy of the dimer. The use of different linker groups led to significant differences in the efficiencies of anodic photocurrent generation. The apparent flat-band potentials evaluated from the photocurrent properties at various pH values and under biased conditions imply that the band structure of the ITO electrode is modified by the anchoring species. The quantum yield for the anodic photocurrent generation by photoexcitation at the Soret band is increased to 15 %, a surprisingly high value without a redox cascade structure on the ITO electrode surface, while excitation at the Q band is not so significant. Extensive exploration of the photocurrent properties has revealed that hot injection of the photoexcited electron from the S2 level into the conduction band of the ITO electrode takes place before internal conversion to the S1* state, through the strong electronic communication of the phosphonyl anchor with the sol-gel-modified ITO surface.     

Solid state-specific and chiral lattice-controlled asymmetric photoisomerization of 3-substituted propyl cobalt complexes, and direct observation of the intermediate complex

Solid state-specific and chiral lattice-controlled asymmetric photoisomerization of 3-cyanopropyl cobaloxime complexes coordinated with chiral axial ligand, 1a-h, was found to occur with moderate to relatively high enantioselectivities (∼91%ee), even though the reaction proceeds through radical species. The enantioselectivities at a lower temperature (−78 °C) are extremely enhanced as compared to those at room temperature, in most cases.The configuration of the major enantiomer of the isomerized product is predictable from the shape of the reaction cavity, drawn based on the crystal structure of the starting material. The structure (including absolute configuration) of the intermediate 2-cyanopropyl complex was directly observed by X-ray crystallographic analyses of a single-crystal-to-single-crystal reaction of (S)-1-cyclohexylethylamine-coordinated 3-cyanopropyl cobaloxime, 1e.     

Single molecular observation of penta- and hexagonic assembly of bisporphyrin on a gold surface

Artificial light-harvesting antennae of coordination-organized macrocyclic porphyrin pentamer and hexamer are visualized by high resolution scanning tunneling microscopy (HRSTM) on a gold surface.