Shinji Toyota

Solvent-free Claisen and Cannizzaro reactions

Abstract Claisen and Cannizzaro reactions were found to proceed efficiently under solvent-free conditions. The solvent-free Claisen reactions were especially effective for the ester substituted with sterically bulky groups, which does not react in solution.

Switching of two amine ligands via an SN2-type mechanism in a coordinated form of 2,6-bis(N,N-dimethylaminomethyl)phenylboronates

Facile exchange between the intramoleculariy coordinated and uncoordinated amine ligands in the title compounds is evidenced by NMR spectroscopy in solution, whereas the dynamic process is frozen in the solid phase as shown by X-ray crystallography.

Construction of novel molecular architectures from anthracene units and acetylene linkers

To create novel π-conjugated compounds, we constructed various molecular architectures from anthracene units and acetylene linkers. Several cyclic oligomers ranging from dimers to dodecamers were synthesized by macrocyclization of acyclic precursors with metal-catalyzed coupling reactions. The structures, dynamic behavior, and spectroscopic features were greatly influenced by the number of anthracene units and the combination of building units and linkers. Optically active and circular dichroism (CD)-active enantiomers of some chiral cyclic oligomers were resolved by chiral high-performance liquid chromatography (HPLC). Conformational analysis of hexamers and higher oligomers was performed with the aid of density functional theory (DFT) calculations. Acyclic oligomers underwent reversible folding–unfolding processes via photochemical and thermal reactions. These results suggest that transannular π–π interactions between anthracene units are important factors in controlling the structural and spectroscopic properties and functions of π-conjugated compounds. The scope and perspectives of this molecular design are discussed on the basis of previous studies.

Ecotoxicity of the degradation products of triphenylborane pyridine (TPBP) antifouling agent

Triphenylborane pyridine (TPBP) is an alternative to organotin antifouling compounds. This work aimed to identify the unknown Peak #1, and to evaluate the ecotoxicity of TPBP and its degradation products. Peak #1 was produced from TPBP dissolved in acetonitrile under UV-A photolysis using a high-pressure mercury lamp. The Peak #1 fraction was purified using two-step column chromatography from a TPBP-acetonitrile solution. The major compound of the fraction was identified as being biphenyl from the 1H NMR and 13C NMR spectra. The ecotoxicity of four degradation products (diphenylborane hydroxide, phenylborane dihydroxide, phenol, and biphenyl) and TPBP towards two marine planktons were assessed. The 48 h LC(50) values of the crustacean, Artemia salina, were 0.13 mg L(-1) for TPBP, 14 mg L(-1) for biphenyl, 17 mg L(-1) for phenol, and > 50 mg L(-1) for the other degradation products. The 72 h EC(50) values of the diatom, Skeletonema costatum, were 0.0022 mg L(-1) for TPBP, 1.2 mg L(-1) for biphenyl, and > 2 mg L(-1) for the other degradation products. Thus, the ecotoxicity of biphenyl and the other degradation products were not high compared to the parent compound, TPBP.

Efficient solvent-free Thorpe reactions

Solvent-free intermolecular and intramolecular Thorpe reactions proceeded efficiently to give acyclic and cyclic enamines, respectively. In the latter case, the reaction products were obtained as colorless crystalline powders just by washing of the reaction mixture with water.

Structure of bis[8-(phenylselanyl)naphthyl] diselenide: first linear alignment of four Se atoms as a four-centre six-electron bond

X-Ray crystallographic analysis of bis[8-(phenylselanyl)naphthyl] diselenide 1 reveals that the four selenium atoms in 1 align almost linearly with the angles of the adjacent three Se atoms 176.9 and 170.3° respectively; the linear bond was shown to be a four-centre six-electron (4c–6e) bond by MO calculations.

Efficient resolution of 2,2′-dihydroxy-1,1′-binaphthyl by inclusion complexation with chiral N-(3-chloro-2-hydroxypropyl)-N,N,N-trimethylammonium chloride

The complete resolution of 2,2[prime or minute]-dihydroxy-1,1[prime or minute]-binaphthyl into its enantiomers by inclusion complexation with a commercially available derivative of choline, is reported. The two enantiomers are recovered in >99% ee from the inclusion complexes by simple dissolution in a diethyl ether-water medium and the resolving agent can be recycled.

Experimental and theoretical investigations of absolute stereochemistry and chiroptical properties of enantiopure 2,2′-substituted 9,9′-bianthryls

Abstract The absolute stereochemistry of axially chiral 2,2′-X 2 -9,9′-bianthryls (X=COOH, COOMe, and Cl) was determined by X-ray analysis of the (+)-quinidine salt of the diacid to be ( M )-(−) or ( P )-(+). The M isomers of these compounds showed specific rotations of −115, −123, and −32, respectively, in acetone. The circular dichroism (CD) as well as UV spectra of the two M isomers (X=COOMe and Cl) were investigated with the aid of theoretical calculations by the time-dependent DFT (TDDFT) method. The calculations reasonably reproduced the observed CD bands, and suggested a correlation between the signs of p or β ′ bands and the absolute stereochemistry.

Chemistry of anthracene–acetylene oligomers. XVII. Synthesis, structure, and dynamic behavior of 1,8-anthrylene pentamers and hexamers with acetylene linkers

Three types of cyclic oligomers consisting of five or six 1,8-anthrylene units with acetylene linkers were synthesized by macrocyclization of the corresponding acyclic precursors with coupling reactions. DFT calculations at the M05/3-21G level revealed that the pentamers had a relatively rigid structure with strained alkyne carbons. Meanwhile, out of several possible conformers the hexamers preferred to take parallelogram-prism structures due to transannular π···π interactions, and conformational interconversions via rotation about the acetylene axes took place rapidly at room temperature. NMR spectra and electronic spectra are discussed on the basis of molecular structures. The enantiomers of the chiral hexamer with one diacetylene linker were resolved by chiral HPLC, and showed optical activity.

Rotational isomerism involving an acetylenic carbon IV: synthesis and structure of bis(1,1′;3′,1″-terphenyl-2′-yl)ethynes: molecular design of sterically congested alkynes toward restricted rotation about acetylenic axis.

The title diphenylethyne derivative with 4-methylphenyl (tolyl) groups at all the ortho positions was synthesized by the Stille or Sonogashira coupling from the corresponding iodide. The X-ray structure revealed that the two terminal phenyl groups at the sp carbons are twisted by 63 degrees out of the coplanar conformation to avoid steric interactions between the tolyl groups. The relative stabilities of possible conformers were analyzed by the PM3 calculations. The axially chiral derivative with two methoxymethyl groups showed no evidence of restricted rotation about the acetylenic axis by VT NMR measurements, its barrier being less than 35 kJ mol(-1). The spectroscopic features and reactivities of this sterically congested alkyne are also described.