Masahiko Yamaguchi

Rhodium-catalyzed substitution reaction of aryl fluorides with disulfides: p-orientation in the polyarylthiolation of polyfluorobenzenes.

In the presence of a catalytic amount of RhH(PPh3)4 and 1,2-bis(diphenylphosphino)benzene, an aromatic fluoride, an organic disulfide (0.5 equiv), and triphenylphosphine (0.5 equiv) reacted in refluxing chlorobenzene to give an aryl sulfide in high yield. Since triphenylphosphine trapped fluoride atoms forming phosphine difluoride, both organothio groups of the disulfide reacted effectively, and the fluoride substituent reacted more readily than the chloride and bromide. The reaction of hexafluorobenzene and a diaryl disulfide gave 1,4-diarylthio-2,3,5,6-tetrafluorobenzene, 1,2,4,5-tetraarylthio-3,6-difluorobenzene, and hexaarylthiobenzene in a stepwise manner; pentafluorobenzene gave 1-arylthio-2,3,5,6-tetrafluorobenzene; 1,2,3,4-tetrafluorobenzene gave 1,2-diarylthio-3,6-difluorobenzene; and 1,2,4,5-tetrafluorobenzene gave 1,4-diarylthio-2-5-difluorobenzene. The polyarylthiolation reaction of polyfluorobenzenes exhibited a strong tendency to form 1,4-difluorobenzenes.

Advances in the Pauson–Khand Reaction: Development of Reactive Cobalt Complexes

Three conceptually new methods employing reactive cobalt carbonyl complexes have been developed for the Pauson-Khand reaction. The first method involves activation of alkyne-dicobalt hexacarbonyls with hard Lewis bases. Primary amines dramatically promote the stoichiometric Pauson-Khand reaction. The active cobalt complexes produced in the system exhibit high reducing ability. The second method involves activation of dicobalt octacarbonyl with less electron-donating hard Lewis bases such as 1,2-dimethoxyethane and water. These Lewis bases were successfully utilized as a promoter for the catalytic Pauson-Khand reaction. The third method employs methylidynetricobalt nonacarbonyl cluster, which exhibits high reactivity in the catalytic Pauson-Khand reaction in the absence of activator. This may be due to facile coordination of the substrate to the metal center through dissociative and associative mechanisms and/or cleavage of one of the cobalt-cobalt bonds.

Chiral recognition in the binding of helicenediamine to double strand DNA: interactions between low molecular weight helical compounds and a helical polymer.

Binding of a helicene, 5,8-bis(aminomethyl)-1,12-dimethylbenzo[c]phenanthrene, to calf thymus DNA was studied using UV, CD, and fluorescence spectroscopy as well as calorimetry. The enantiomeric helicenes strongly bound to the double strand DNA possessing the right-handed helical structure. In addition, chiral recognition was observed in the binding, where the (P)-helicene with the right-handed helicity formed more stable complex than the (M)-helicene with the left-handed helicity. The binding studies of the helicenes and natural nucleosides by 1H NMR spectroscopy also revealed the higher affinity to the (P)-helicene. Both monomeric and polymeric nucleic acids thus turned out to favor the (P)-helicity.

Enantioselective hydrogenation of itaconate using rhodium bihelicenol phosphite complex. Matched/mismatched phenomena between helical and axial chirality

Abstract Phosphites prepared from bihelicenol, menthol (or 1-phenylethanol), and PCl3 are effective ligands for the rhodium-catalyzed enantioselective hydrogenation of dimethyl itaconate. Stereochemistry of the helicene moiety plays an important role in the asymmetric induction, and matched/mismatched phenomena are observed between helical and axial chirality.

Transition-metal-catalyzed synthesis of organosulfur compounds

Rhodium complexes are efficient catalysts for the synthesis of organosulfur compounds. They catalyze the addition reaction of organosulfur groups to unsaturated compounds, the substitution of C-H with organosulfur groups, and single-bond metathesis reactions. They cleave S-S bonds and transfer the organosulfur groups to various organic and inorganic molecules, including alkynes, allenes, disulfides, sulfur, isonitriles, imines, diphosphines, thiophosphinites, hydrogen, 1-alkylthio-1-alkynes, thioesters, and allyl sulfides.

Synthesis of optically active bihelicenols

All six stereoisomers of dimethyl 5,5′-dihydroxy-1,1′,12,12′-tetramethyl-[6,6′]bi(benzo[c]phenanthrenyl)-8,8′-dicarboxylate (bihelicenol) were synthesized by the oxidative coupling of methyl 8-hydroxy-1,12-dimethylbenzo[c]phenanthrene-5-carboxylate (helicenol), and their structures were determined by X-ray analysis.

Trichlorogallium and trialkylgalliums in organic synthesis

Organic gallium compounds formed by the interactions of organic compounds with trichlorogallium or trialkylgalliums exhibit various reactivities, and their use in organic synthesis is described.

Rhodium-Catalyzed Methylthio Transfer Reaction between Ketone α-Positions: Reversible Single-Bond Metathesis of C−S and C−H Bonds

In the presence of a catalytic amount of RhH(PPh(3))(4) and 1,2-bis(diphenylposphino)ethane (dppe), alpha-phenylthio ketones were methylthiolated with p-cyano-alpha-methylthioacetophenone giving alpha-phenylthio-alpha-methylthio ketones. The methylthio transfer reaction between the ketone alpha-positions was reversible and at equilibrium, and the methylthio group was transferred in preference to the phenylthio group. The reaction of tertiary alkyl methylthiomethyl ketones proceeded in high yields; the reaction of diastereomeric 4-(tert-butyl)-2-phenylthiocyclohexanones gave an axial 2-methylthiolated product.

Synthesis and monolayer behaviors of optically active 1,12- dimethylbenzo[c]phenanthrene-5,8-diamides and the formation of chiral langmuir-blodgett films

Abstract We previously reported that an optically active cyclic amide consisting of a helical chiral 1,12-dimethylbenzo[c]phenanthrene-5, 8-dicarboxylic acid forms a stable monolayer on the water surface, and that the monolayer can be transferred on a solid support giving optically active Langmuir-Blodgett (LB) films. In this study, several related amides were synthesized, and their monolayer behaviors were investigated with expectation to prepare optically active LB films possessing functional groups. The result indicates that the cyclic amide structure and cyclohexyl moiety are essential for the formation of stable monolayer on the water surface. N-Alkylation of the secondary amide does not seriously affect the formation of monolayer, and chiral LB films are obtained by N,N-bis(3-meroaptopropyl) derivative of the cyclic amide.

Folding of dihelicenetriamines in water

Diastereomeric triamines containing two helicene moieties, 1,12-dimethylbenzo[c]phenanthrene, were synthesized and found to form folded structures in the water. Such folding was not observed for an achiral compound possessing a naphthalene moiety. The (M,M)-dihelicenetriamine with matching configuration at the helicene moieties formed a more stable folded structure than the (P,M)-isomer containing two enantiomeric helicene groups. The most stable folded conformation was predicted by the Monte Carlo method with Amber force field of the dihelicenetriamine.