PIFA-mediated oxidative cycloisomerization of 2-propargyl-1,3-dicarbonyl compounds: divergent synthesis of furfuryl alcohols and furfurals

PhI(OCOCF₃)₂ (PIFA) in the presence of trifluoroacetic acid (TFA) in CH₂Cl₂ efficiently promotes the oxidative cycloisomerization of 2-propargyl 1,3-dicarbonyl compounds to give 4,5-disubstituted furfuryl alcohols. PIFA in hexafluoroisopropanol (HFIP) or PIFA-BF₃·OEt₂ in CH₂Cl₂ bring about the direct formation of furfurals from 2-propargyl 1,3-dicarbonyl compounds. In a few cases, PhIO is suitable for the direct formation of furfurals.     

Cage-shaped borate esters with tris(2-oxyphenyl)methane or -silane system frameworks bearing multiple tuning factors: geometric and substituent effects on their Lewis acid properties

Boron complexes that contain new tridentate ligands, tris(o‐oxyaryl)methanes and ‐silanes, were prepared. These complexes had a cage‐shaped structure around a boron center and showed higher Lewis acidity and catalytic activity than open‐shaped boron compounds. The cage‐shaped ligands determined the properties of the borates by altering the geometry and were consistently bound to the metal center by chelation. The synthesized compounds were L?B(OC₆H₄)₃CH, L?B(OC₆H₄)₃SiMe, and its derivatives (L=THF or pyridine as an external ligand). Theoretical calculations suggested that the cage‐shaped borates had a large dihedral angle (C_ipso‐O‐B‐O) compared with open‐shaped borates. The geometric effect due to the dihedral angle means that compared with open‐shaped, the cage‐shaped borates have a greater Lewis acidity. The introduction of electron‐withdrawing groups on the aryl moieties in the cage‐shaped framework increased the Lewis acidity. Substitution of a bridgehead Si for a bridgehead C decreased the Lewis acidity of the boron complexes because the large silicon atom reduces the dihedral angle of C_ipso‐O‐B‐O. The ligand‐exchange rates of the para‐fluoro‐substituted compound B(OC₆H₃F)₃CH and the ortho‐phenyl‐substituted compound B(OC₆H₃Ph)₃CH were less than that of the unsubstituted borate B(OC₆H₄)₃CH. The ligand‐exchange rate of B(OC₆H₄)₃SiMe was much faster than that of B(OC₆H₄)₃CH. A hetero Diels–Alder reaction and Mukaiyama‐type aldol reactions were more effectively catalyzed by cage‐shaped borates than by the open‐shaped borate B(OPh)₃ or by the strong Lewis acid BF₃?OEt₂. The cage‐shaped borates with the bulky substituents at the ortho‐positions selectively catalyzed the reaction with less sterically hindered substrates, while the unsubstituted borate showed no selectivity.     

Efficient direct electron transfer with enzyme on a nanostructured carbon film fabricated with a maskless top-down UV/ozone process

We have developed a new carbon film electrode material with thornlike surface nanostructures to realize efficient direct electron transfer (DET) with enzymes, which is very important for various enzyme biosensors and for anodes or cathodes used in biofuel cells. The nanostructures were fabricated using UV/ozone treatment without a mask, and the obtained nanostructures were typically 2-3.5 nm high as confirmed by atomic force microscopy measurements. X-ray photoelectron spectroscopy and transmission electron microscopy revealed that these nanostructures could be formed by employing significantly different etching rates depending on nanometer-order differences in the local sp(3) content of the nanocarbon film, which we fabricated with the electron cyclotron resonance sputtering method. These structures could not be realized using other carbon films such as boron-doped diamond, glassy carbon, pyrolyzed polymers based on spin-coated polyimide or vacuum-deposited phthalocyanine films, or diamond-like carbon films because those carbon films have relatively homogeneous structures or micrometer-order crystalline structures. With physically adsorbed bilirubin oxidase on the nanostructured carbon surface, the DET catalytic current amplification was 30 times greater than that obtained with the original carbon film with a flat surface. This efficient DET of an enzyme could not be achieved by changing the hydrophilicity of the flat carbon surface, suggesting that DET was accelerated by the formation of nanostructures with a hydrophilic surface. Efficient DET was also observed using cytochrome c.     

Edge-defined film-fed growth of Yb:YVO4 single crystal plates

The applicability of the edge-defined film-fed growth (EFG) technique for Yb_xY_(1−x)VO₄ (x=0.05, 0.1 and 1) was approved by successful growth of crystals up to 80 mm in length as the thin plates. Low-angle grain boundaries and the crystal coloration as main defects were found. Optimal seed orientation was suggested on the strength of vanadate crystal plate morphology. Optical properties, chemical composition and the crystalline quality were investigated.     

Synthesis and Some Properties of Low Melting Ferroelectric Liquid Crystals of Benzylidene Anilines

A series of chiral benzylidene-aniline compounds, 4-alkoxybenzylidene 4′-(2-methylbutyloxycarbonyl)anilines, have been synthesized and their mesomorphic properties are examined. They showed a monotropic chiral smectic C phase in conjunction with enantiotropic smectic A phase, and their chiral smectic C—smectic A phase transition temperatures are around room temperatures. Their spontaneous polarization values are moderately higher than those of DOBAMBC “4-decyloxybenzylidene 4′-amino-(2-methylbutyl)cinnamate”.     

Selective reduction of tertiary alkyl,benzyl, and allyl halides to hydrocarbons using lithium 9,9-di-n-butyl-9-borabicyclo[3.3.1]nonanate

The title 9-borabicyclo[3.3.1]nonane(9-BBN) ate complex (1) brings about selective removal of tertiary alkyl, benzyl and allyl halides to give the corresponding hydrocarbons in excellent yields without concomitant attack on secondary, primary and aryl derivatives. The reduction of cis- and trans - 4 - t - butyl - 1 - methylcyclohexyl chlorides (2) with 1 gives 4 - t - butyl - 1 - methylcyclohexanes (3) with partial inversion of configuration in cyclohexane, while that in benzene gives thermodynamically stable trans-3 predominantly. The reactions of 1,1 - dimethyl - 5 - hexenyl chloride (4) and 1,7,7 - trimethylbicyclo[2.2.1]hept - 2 - yl chloride (8) with 1 proceed with the rearrangements characteristic to a carbonium ion intermediate. The reduction of 1 - ethyl - 1 - methylpentyl chloride with 1 follows a second-order rate equation.     

Design of Ratiometric Fluorescent Probes Based on Arene–Metal‐Ion Interactions and Their Application to CdII and Hydrogen Sulfide Imaging in Living Cells

Non‐coordinative interactions between a metal ion and the aromatic ring of a fluorophore can act as a versatile sensing mechanism for the detection of metal ions with a large emission change of fluorophores. We report the design of fluorescent probes based on arene–metal‐ion interactions and their biological applications. This study found that various probes having different fluorophores and metal binding units displayed significant emission redshift upon complexation with metal ions, such as Ag^I, Cd^II, Hg^II, and Pb^II. X‐ray crystallography of the complexes confirmed that the metal ions were held in close proximity to the fluorophore to form an arene–metal‐ion interaction. Electronic structure calculations based on TDDFT offered a theoretical basis for the sensing mechanism, thus showing that metal ions electrostatically modulate the energy levels of the molecular orbitals of the fluorophore. A fluorescent probe was successfully applied to the ratiometric detection of the uptake of Cd^II ions and hydrogen sulfide (H₂S) in living cells. These results highlight the utility of interactions between arene groups and metal ions in biological analyses.     

Neomacrophorin I,II, and III,novel drimenyl cyclohexanes with hydroxylated butanoates from Trichoderma sp. 1212-03

Neomacrophorins I (1), II (2), and III (3) were isolated from the culture broth of Trichoderma sp. 1212-03, which was collected at Shirakami Mountainous area in Japan. Structural analyses disclosed that these resemble known macrophorins but possess axial-hydroxy group at C3 as well as different side chains at C7′. These are diastereomeric forms of macrophorins for 5′,6′-epoxide functionality. The NMR analyses suggested their relative configurational relationship between the C1–C15 drimene and C1′–C7′ epoxyquinone moieties. ECD spectral discussions verified them particularly for C5′,C6′-epoxyquinone (1), C5′,C6′-epoxysemiquinone (2 and 3), and 2″,3″-dihydroxybutanoate moiety in 1 and 2. The configuration of C3″-stereocenter of 3 was determined by chiral GC–MS after converting into methyl (S)-3″-hydroxybutanoate by basic of 3 methanolysis. Biological assays disclosed that 1 induces hyphal branching of Cochliobolus miyabeanus as well as cytotoxicity against human colorectal cancer COLO 201.