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The first enantioselective carbometalation reaction of azabicycloalkenes has been achieved by iron catalysis to in situ form optically active organozinc intermediates, which are amenable to further synthetic elaborations. The observed chiral induction, along with the DFT and XAS analyses, reveals the direct coordination of the chiral phosphine ligand to the iron centre during the carbon–carbon and carbon–metal bond forming step. This new class of iron-catalysed asymmetric reaction will contribute to the synthesis and production of bioactive molecules.

The first iron-catalyzed cross-coupling reaction of alkyl halides with alkylaluminum reagents (alkyl–alkyl Negishi coupling) is developed using an iron/bisphosphine catalyst system. The reaction shows high functional group tolerance: various primary alkyl halides possessing a non-protected indole, carboxyl, or hydroxy group are coupled with primary alkylaluminum reagents in good yields. Potassium fluoride plays a key role to promote the reaction by generating an aluminate species, which facilitates the transmetalation between the organoaluminum and the iron catalyst.

We have developed novel surface plasmon resonance (SPR) sensor chips whose surfaces bear newly synthesized functional self-assembled monolayer (SAM) anchoring lignin through covalent chemical bonds. The SPR sensor chips are remarkably robust and suitable for repetitive and accurate measurement of noncovalent lignin–peptide interactions, which is of significant interest in the chemical or biochemical conversion of renewable woody biomass to valuable chemical feedstocks. The lignin-anchored SAMs were prepared for the first time by click chemistry based on an azide–alkyne Huisgen cycloaddition: mixed SAMs are fabricated on gold thin film using a mixture of alkynyl and methyl thioalkyloligo(ethylene oxide) disulfides and then reacted with azidated milled wood lignins to furnish the functional SAMs anchoring lignins covalently. The resulting SAMs were characterized using infrared reflection–absorption, Raman, and X-ray photoelectron spectroscopies to confirm covalent immobilization of the lignins to the SAMs via triazole linkages and also to reveal that the SAM formation induces a helical conformation of the ethylene oxide chains. Further, SPR measurements of the noncovalent lignin–peptide interactions using lignin-binding peptides have demonstrated high reproducibility and durability of the prepared lignin-anchored sensor chips.

We have developed a novel diastereoselective iron-catalyzed cross-coupling reaction of various glycosyl halides with aryl metal reagents for the efficient synthesis of aryl C-glycosides, which are of significant pharmaceutical interest due to their biological activities and resistance toward metabolic degradation. A variety of aryl, heteroaryl, and vinyl metal reagents can be cross-coupled with glycosyl halides in high yields in the presence of a well-defined iron complex, composed of iron(II) chloride and a bulky bisphosphine ligand, TMS-SciOPP. The chemoselective nature of the reaction allows the use of synthetically versatile acetyl-protected glycosyl donors and the incorporation of various functional groups on the aryl moieties, producing a diverse array of aryl C-glycosides, including Canagliflozin, an inhibitor of sodium-glucose cotransporter 2 (SGLT2), and a prevailing diabetes drug. The cross-coupling reaction proceeds via generation and stereoselective trapping of glycosyl radical intermediates, representing a rare example of highly stereoselective carbon-carbon bond formation based on iron catalysis. Radical probe experiments using 3,4,6-tri-O-acetyl-2-O-allyl-α-d-glucopyranosyl bromide (8) and 6-bromo-1-hexene (10) confirm the generation and intermediacy of the corresponding glycosyl radicals. Density functional theory (DFT) calculations reveal that the observed anomeric diastereoselectivity is attributable to the relative stability of the conformers of glycosyl radical intermediates. The present cross-coupling reaction demonstrates the potential of iron-catalyzed stereo- and chemoselective carbon-carbon bond formation in the synthesis of bioactive compounds of certain structural complexity.

A series of norvaline (Nva) peptides possessing ONO-pincer ruthenium complexes, Boc-{l-[Ru(pydc)(t-Bu-terpy)]Nva}n-OMe (n = 2–6), were synthesized successfully by solution-phase peptide synthesis. Efficient coupling of equimolar amounts of N-free Ru-bound norvaline peptides, H-{l-[Ru(pydc)(t-Bu-terpy)]Nva}n-OMe, and C-free Ru-bound norvaline, Boc-l-[Ru(pydc)(t-Bu-terpy)]Nva-OH, was achieved by using the 2-chloro-4,6-dimethoxy-1,3,5-triazine-based method. Structural analysis by means of CD and NMR spectroscopy revealed the formation of stable helical conformations in peptides more than three residues.

Two (ONO pincer)ruthenium‐complex‐bound norvalines, Boc−[Ru(pydc)(terpy)]Nva−OMe (1; Boc=tert‐butyloxycarbonyl, terpy=terpyridyl, Nva=norvaline) and Boc−[Ru(pydc)(tBu‐terpy)]Nva−OMe (5), were successfully synthesized and their molecular structures and absolute configurations were unequivocally determined by single‐crystal X‐ray diffraction. The robustness of the pincer Ru complexes and norvaline scaffolds against acidic/basic, oxidizing, and high‐temperature conditions enabled us to perform selective transformations of the N‐Boc and C−OMe termini into various functional groups, such as alkyl amide, alkyl urea, and polyether groups, without the loss of the Ru center or enantiomeric purity. The resulting dialkylated Ru‐bound norvaline, n‐C11H23CO−l‐[Ru(pydc)(terpy)]Nva−NH‐n‐C11H23 (l‐4) was found to have excellent self‐assembly properties in organic solvents, thereby affording the corresponding supramolecular gels. Ru‐bound norvaline l‐1 exhibited a higher catalytic activity for the oxidation of alcohols by H2O2 than parent complex [Ru(pydc)(terpy)] (11 a).

Solution-phase synchrotron X-ray absorption spectroscopy (XAS) is a powerful tool for structural and mechanistic investigations of paramagnetic organoiron intermediates in solution-phase reactions. For paramagnetic organotransition metal intermediates, difficulties are often encountered with conventional NMR- and EPR-based analyses. By using solution-phase XAS, we succeeded in identifying the organoiron species formed in the reaction of iron bisphosphine with mesitylmagnesium bromide, MesMgBr, and 1-bromodecane in a [FeX2(SciOPP)]-catalyzed Kumada–Tamao–Corriu (KTC)-type cross-coupling reaction. X-ray absorption near-edge structure (XANES) spectra showed that the resulting aryliron species possessed a divalent oxidation state. Extended X-ray absorption fine structure (EXAFS) demonstrated that the solution-phase molecular geometries of these species are in satisfactory agreement with the crystallographic geometries of [FeIIBrMes(SciOPP)] and [FeIIMes2(SciOPP)]. By combining GC-quantitative analysis and solution-phase XAS, the cross-coupling reactivities of these aryliron species were successfully investigated in the reaction with 1-bromodecane under stoichiometric and catalytic conditions., 放射光施設SPring-8で鉄触媒の作用を直接観察. 京都大学プレスリリース. 2015-03-16.

The NCN-pincer Pd-complex-bound norvalines Boc-D/L-[PdCl(dpb)]Nva-OMe (1) were synthesized in multigram quantities. The molecular structure and absolute configuration of 1 were unequivocally determined by single-crystal X-ray structure analysis. The robustness of 1 under acidic/basic conditions provides a wide range of N-/C-terminus convertibility based on the related synthetic transformations. Installation of a variety of functional groups into the N-/C-terminus of 1 was readily carried out through N-Boc- or C-methyl ester deprotection and subsequent condensations with carboxylic acids, R(1)COOH, or amines, R(2)NH2 , to give the corresponding N-/C-functionalized norvalines R(1)-D/L-[PdCl(dpb)]Nva-R(2) 2-9. The dipeptide bearing two Pd units 10 was successfully synthesized through the condensation of C-free 1 with N-free 1. The robustness of these Pd-bound norvalines was adequately demonstrated by the preservation of the optical purity and Pd unit during the synthetic transformations. The lipophilic Pd-bound norvalines L-2, Boc-L-[PdCl(dpb)]Nva-NH-n-C11H23, and L-4, n-C4H9CO-L-[PdCl(dpb)]Nva-NH-n-C11H23, self-assembled in aromatic solvents to afford supramolecular gels. The assembled structures in a thermodynamically stable single crystal of L-2 and kinetically stable supramolecular aggregates of L-2 were precisely elucidated by cryo-TEM, WAX, SAXS, UV/Vis, IR analyses, and single-crystal X-ray crystallography. An antiparallel β-sheet-type aggregate consisting of an infinite one-dimensional hydrogen-bonding network of amide groups and π-stacking of PdCl(dpb) moieties was observed in the supramolecular gel fiber of L-2, even though discrete dimers are assembled through hydrogen bonding in the thermodynamically stable single crystal of L-2. The disparate DSC profiles of the single crystal and xerogel of L-2 indicate different thermodynamics of the molecular assembly process.

Novel Pt-complex-bound oligo(glutamic acid)s were synthesized by two different routes: postmetalation of peptides and stepwise conjugation of metalated amino acids. Sonication-induced supramolecula...

In this research, we report the development, characterization and application of various plasmonic substrates (with localized surface plasmon resonance wavelength tunable by gold nanoparticle size) for two-photon absorption (TPA)-induced photodimerization of an anthracene derivative, anthracene carboxylic acid, in both surface and solution phase under incoherent visible light irradiation. Despite the efficient photoreaction property of anthracene derivatives and the huge number of publications about them, there has never been a report of a multiphoton photoreaction involving an anthracene derivative with the exception of a reverse photoconversion of anthracene photodimer to monomer with three-photon absorption. We examined the progress of the TPA-induced photoreaction by means of surface-enhanced Raman scattering, taking advantage of the ability of our plasmonic substrate to enhance and localize both incident light for photoreaction and Raman scattering signal for analysis of photoreaction products. The TPA-induced photoreaction in the case of anthracene carboxylic acid coated 2D array of gold nanoparticles gave different results according to the properties of the plasmonic substrate, such as the size of the gold nanoparticle and also its resultant optical properties. In particular, a stringent requirement to achieve TPA-induced photodimerization was found to be the matching between irradiation wavelength, localized surface plasmon resonance of the 2D array, and twice the wavelength of the molecular excitation of the target material (in this case, anthracene carboxylic acid). These results will be useful for the future development of efficient plasmonic substrates for TPA-induced photoreactions with various materials.

The dimerization reactions of 2-bromo-3,5,6-trimethyl-1,4-benzoquinone have been examined. 2,2′-Dimeric benzoquinone was prepared via a Stille-type homocoupling, whereas an oxepin was formed by the...

An NCN-pincer Pd-complex-bound norvaline-based supramolecular gel showed efficient catalytic activities for the intramolecular addition–cyclization of alkynoic acid and phenol derivatives in water ...

Novel NCN-pincer Pd-complex-bound norvaline derivatives were synthesized. The N- and C-termini-alkylated Pd–norvalines spontaneously assemble into fibrous aggregates to form supramolecular gels, in...

The title molecule, C44H30O8, lies about a crystallographic inversion centre located at the centre of the central benzene ring. The benzene rings in the benzoyl and the terephthalate units make dihedral angles of 67.05 (7)° and 57.57 (7)°, respectively, with the naphthalene ring system. There is an intramolecular C—H...O interaction between the ketonic carbonyl O atom and an H atom on the naphthalene ring system. In the crystal, C—H...O interaction of the benzene ring in the benzoyl group and weak C=O...π interaction [O...centroid = 3.375 (2) Å] of the naphthalene ring with the O atom in the ketonic carbonyl group are observed. These interactions form layers parallel to the bc plane.

Boron-modified pyrrole-based anion receptors (catechol–boron and diphenylboron dipyrrolyldiketone derivatives) formed planar receptor–anion complexes, leading to charge-by-charge assemblies with planar cations, as in the corresponding difluoroboron derivative.

A new type of Pt-complex-bound amino acid was synthesized by condensation of a cyclometalated Pt complex with the side-chain residue of N- and C-alkylated glutamic acid. Self-assembly of the Pt-bound lipophilic amino acid afforded a supramolecular gel in organic solvents, which comprised fibrous lamellar aggregates that supported a highly oriented Pt array.

A novel DNA base-pairing beta-hairpin peptide involving intramolecular hydrogen bonds for induction of beta-hairpin secondary structure and intermolecular complementary hydrogen bonds between thymine and diaminopyridine for molecular recognition has been synthesized.

In the mol­ecule of the title compound, C28H22F2O4, the benzoyl groups are aligned almost anti­parallel and the fluorobenzene rings form a dihedral angle of 14.12 (7)°. The dihedral angles between the 2,7-dieth­oxy­naphthalene ring system and the benzene rings are 70.00 (4) and 67.28 (4)°. In the crystal, mol­ecules are linked by C—H⋯O and C—H⋯F hydrogen bonds, forming layers parallel to the ab plane. The layers are further connected by π–π inter­actions [centroid–centroid distances of 3.6115 (10) Å] into a three-dimensional structure.

The molecule of the title compound, C26H18F2O8S2, lies across a crystallographic twofold rotation axis. The benzene rings of the 4-fluorobenzoyl groups make dihedral angles of 78.93 (12)° with the naphthalene ring system. An intramolecular C—H...π interaction occurs. In the crystal, a number of C—H...O interactions link the molecules, forming a three-dimensional structure.

The title compound, [Pt(C15H18NO2S)Cl], was obtained by the cyclo­metallation reaction of cis-bis­(benzonitrile)dichlorido­platinum(II) with N-benzyl­idene-l-methio­nine allyl ester in refluxing toluene. The PtII atom has a square-planar geometry and is tetra-coordinated by the Cl atom and the C, N and S atoms from the benzyl­idene methio­nine ester ligand. In the crystal structure, the S atoms show opposite chiral configurations with respect to the α-carbon of the methio­nine, reducing steric repulsion between the methyl and allyl ester groups.