An asymmetric synthesis of (+)-monomorine I

The synthesis of (+)-monomorine I, an indolizidine alkaloid isolated from Monomorium pharaonis, has been achieved. The 2,6-cis-piperidine ring moiety of (+)-monomorine I was constructed using diastereoselective aminopalladation. Chain elongation via cross-metathesis using Hoveyda-Grubbs 2nd catalyst followed by deprotection of the Cbz group and cyclic reductive hydroamination afforded (+)-monomorine I.     

Total synthesis of (+)-azimine via diastereoselective aminopalladation

The aminopalladation of amino allylic alcohol using Cl₂Pd(MeCN)₂ in CH₂Cl₂ gave the 2,6-disubstituted piperidine with excellent diastereoselectivity. This compound was successfully converted into (+)-azimine (1) using cross-metathesis and Shiina macrolactonization.     

Charge-Transfer Interactions of Aluminum Copper(I) Chloride with Polystyrene and Related Compounds

Interactions between polystyrene and aluminum copper(I) chloride (AlCuCl₄) were investigated by various spectroscopic measurements in order to elucidate the structure of polystyrene-AlCuCl₄ complex in solution and the mechanism of water resistance of the complex as a carbon monoxide absorbent. The chemical shift (101 ppm) and half line width (145 Hz) of AlCuCl₄ in benzene by ²⁷Al-NMR suggest a dimer structure bridged by two chlorine atoms, which is almost identical with that of aluminum chloride. The coordination of benzene or other aromatic compounds to AlCuCl₄ was confirmed by charge-transfer bands in UV and visible absorptions. The equilibrium constants (K) for complex formation of AlCuCl₄ with various aromatic compounds were determined by ¹³C-NMR spectroscopy. In the case of AlCuCl₄ and benzene in 1,2-dichloroethane, for example, K is 2.2 M ^?1 at 303 K. For the polymer complex solution and 1,3-diphenyl-propane solution, strong charge-transfer bands have been observed in the wavelength region at about 380 to 500 nm, where no band is observed in benzene derivatives. This strong charge-transfer band is considered to be due to the strong interaction of AlCuCl₄ with adjacent aromatic rings of polystyrene or 1,3-diphenylpropane of a chelate type, which, as a result, causes the water resistance of the present carbon monoxide absorbent system.     

Polymerized Micelle-Protected Platinum Clusters. Preparation and Application to Catalyst for Visible Light-Induced Hydrogen Generation

Platinum clusters protected by polymerized micelles were prepared by radical polymerization of unsaturated surfactants which were involved in micelle-protected platinum clusters. The micelle-protected platinum clusters were successfully prepared by photoreduction of hexachloroplatinic acid in water in the presence of unsaturated surfactants. The platinum clusters thus obtained were characterized by electron microscopy and IR and ¹H-NMR spectroscopies. The average diameter of the platinum particles was about 1 nm by electron microscopy, and the polymerization was confirmed by IR and ¹H-NMR spectra. The platinum clusters thus obtained proved to be highly active catalysts for visible light-induced hydrogen generation in the system of EDTA/Ru(bpy)₃ ²⁺/MV²⁺. The polymerized micelle-protected platinum clusters showed higher catalytic activity than the linear polymer-protected one. The catalytic activity was affected by the electric charge of the surfactants in the polymerized micelle-protected platinum clusters. Nonionic polymers were superior to those having anionic and cationic hydrophilic groups from the viewpoint of catalytic activity. The nonionic polymerized micelle forms rigid hydrophobic cores which help charge separation and the formation of a sequential potential field.     

Formation and Catalytic Functionality of Synthetic Polymer-Noble Metal Colloid

Colloidal dispersions of noble metals in synthetic polymers are prepared by reduction with alcohol. Reflux of a solution of rhodium(III) chloride and poly(vinyl alcohol) (PVA) in a methanol-water mixed solvent under argon or air for 4 hr gives a homogeneous solution of colloidal dispersion of rhodium (Rh-PVA-MeOH/H₂O). The particle size of metallic rhodium is distributed n a narrow range of 30-70 Å, and the average diameter is 40 A. The formation of colloidal rhodium proceeds through three steps: coordination of poly(vinyl alcohol) to rhodium(III) ion, reduction with methanol to form small particles (8 Å in diameter), and growth of the small particle to large particle (40 Å in diameter). Polyvinylpyrrolidone (PVP) and poly(methyl vinyl ether) (PMVE) can be used in place of poly(vinyl alcohol) and result in colloidal dispersions, respectively, similar to Rh-PVA-MeOH/H₂O. Colloidal dispersions in nonaqueous solvent can be prepared by using ethanol instead of methanol-water (Rh-PVP-EtOH) and by using methanol instead of methanol-water, with addition of small amount of methanol solution of sodium hydroxide (Rh-PVP-MeOH/NaOH). The average diameters of rhodium particles in Rh-PVP-EtOH and Rh-PVP-MeOH/NaOH are 22 and 9 Å, respectively. The colloidal dispersions of palladium, silver, osmium, iridium, platinum, and gold in aqueous or nonaqueous solvent are prepared by using polyvinylpyrrolidone. The colloidal dispersions are very stable even under air for 20 days. Those of rhodium, palladium, and platinum are effective catalysts for hydrogenation of olefins at 30°C under an atmospheric hydrogen pressure. The colloidal dispersion of palladium catalyzes highly selective hydrogenation of diene and dienoate to monoene and monoenoate, respectively.     

Semi-metallic single-component crystal of soluble La@C82 derivative with high electron mobility

We prepared an organic conductor crystal having extremely high electron mobility, in which the adamantylidene (Ad) derivative of La@C(82) (an endohedral metallofullerene known as a n-type semiconductor) is aligned in an orderly fashion. The single-component crystal exhibits high electron mobility of μ > 10 cm(2) V(-1) s(-1) along the c axis under normal temperatures and pressures in the atmosphere, as shown by flash-photolysis time-resolved microwave conductivity (TRMC) measurements, which are the highest of reported organic conductors measured by TRMC. According to density functional calculations, the single crystal of La@C(82)Ad is semi-metallic, with a small band gap of 0.005 eV.     

Synthesis of pyranicin and its deoxygenated analogues and their inhibitory action with bovine heart mitochondrial complex I

Total synthesis of pyranicin and its deoxygenated analogues was achieved using Cl₂Pd(CH₃CN)₂ catalyzed diastereoselective cyclization of the allylic ester as the key step. The inhibitory activity of these compounds for mitochondrial NADH-ubiquinone oxidoreductase (complex I) was poorer than those of ordinary mono-THF acetogenins such as annonacin.     

Practical, general, and systematic method for optical resolution of gem-dihalo- and monohalocyclopropanecarboxylic acids utilizing chiral 1,1'-binaphtholmonomethyl ethers: application to the synthesis of three chiral pesticides

We performed an efficient practical and systematic optical resolution method for gem-dihalo- and monohalocyclopropanecarboxylic acids and utilizing chiral 1,1'-binaphthol monomethyl ether (R)- as the key auxiliary. Direct esterification of with (R)- gave two 1R- and 1S-diastereomeric esters with marked different R(f) values, both of which were easily separated using simple column chromatography. Monodehalogenation of separated chiral esters using t-BuMgCl and cat. Co(dppe)(2)Cl(2) gave two 1,2-trans- and 1,2-cis-diastereomers with markedly different R(f) values, both of which were similarly separated using simple column chromatography. The obtained diastereomers and were easily hydrolyzed to the desired enantiopure acids (>99%) and (>99%), respectively, with recovery of (R)-, both in good to excellent yields. Utilizing the present method, important chiral agrochemicals, carpropamid and fencyclate , were readily synthesized. Pyrethroid with three asymmetric centers was efficiently synthesized in a much better yield compared with the reported method.     

Tin-free Giese reaction and the related radical carbonylation using alkyl iodides and cyanoborohydrides

Tin-free Giese reaction and the related radical carbonylation process proceeded efficiently in the presence of sodium cyanoborohydride and tetrabutylammonium cyanoborohydride. The reaction took place chemoselectively at the carbon-iodine bond but not at the carbon-bromine and carbon-chlorine bonds. The iodine atom transfer followed by hydride reduction of the resulting carbon-iodine bond is proposed as a possible mechanism.