Kouichi Ohe

PD(OAC)2-CATALYZED OXIDATION OF ALCOHOLS TO ALDEHYDES AND KETONES BY MOLECULAR OXYGEN

A novel combination of Pd(OAc)2/pyridine/MS3A catalyzes the aerobic oxidation of various benzylic alcohols into corresponding aldehydes and ketones in good yield. Primary and secondary aliphatic alcohols also are smoothly oxidized to aldehydes and ketones, respectively, under the same conditions.

A new ruthenium-catalyzed cyclopropanation of alkenes using propargylic acetates as a precursor of vinylcarbenoids

Abstract [RuCl 2 (CO) 3 ] 2 catalyzes intermolecular cyclopropanation of various alkenes with propargylic acetates to give vinylcycloropanes in good yields. The key intermediate of this reaction is a vinylcarbene complex generated by nucleophilic attack of the carbonyl oxygen of the acetate to an internal carbon of alkyne activated by the ruthenium complex.

Palladium-catalyzed asymmetric intermolecular arylation of cyclic or acyclic alkenes using phosphinite-oxazoline ligands derived from d-glucosamine

Abstract Chiral phosphinite-oxazolines, 2-alkyl- or 2-aryl-4,5-(4,6-O-benzylidene-3-O-(diphenylphosphino)-1,2-di-deoxy-α- d -glucopyranosyl)-[2,1-d]-2-oxazolines 1a–f derived from d -glucosamine hydrochloride, are revealed to work as effective P,N-bidentate ligands in the palladium-catalyzed enantioselective arylation of 2,3-dihydrofuran to give 2-aryl-2,5-dihydrofuran selectively in high yield with up to 96% ee. The first asymmetric phenylation reaction of trans- and cis-crotyl alcohols as acyclic alkenes with iodobenzene is also carried out to afford 3-phenylbutanal in moderate chemical yield with up to 17% ee. The complex [PdCl2(1b)] is newly prepared and its structure is characterized by X-ray crystallography. Structures of the new complex [(p-MeO2CC6H4)PdI(1a)] (8) and its cationic complex [(p-MeO2CC6H4)Pd(1a)]+OTf− (9) are also elucidated on the basis of 1H-, 13C-, and 31P-NMR spectra, p-MeO2CC6H4 moiety on the palladium being located trans to the nitrogen of 1a. This configuration might be responsible for an enantiofacial discrimination of 2,3-dihydrofuran to produce (R) isomer predominantly. The stoichiometric reaction of [PhPd(1f)]+OTf− (11) with 2,3-dihydrofuran has provided the mechanistic aspect for the arylation using P,N-ligands, in which the base-promoted deprotonation at β-position leading to an alkene(2-aryl-2,5-dihydrofuran)–palladium(0) complex has been shown to be an important step for the selective formation of the product.

Palladium(II)-catalyzed phenylation of unsaturated compounds using phenylantimony chlorides under air ☆

Abstract Diphenylantimony chloride and phenylantimony dichloride, mainly the former, react smoothly with alkenes in acetonitrile at r.t. in the presence of a catalytic amount of Pd(OAc) 2 under air to afford the corresponding phenylated alkenes (Heck-type reaction). The addition of AgOAc as reoxidant is not necessary for this reaction in sharp contrast to similar reactions using triarylstibines. The oxygen absorption is confirmed in this catalytic reaction and the reaction does not proceed catalytically in palladium(II) under inert gases, such as nitrogen or argon. Even under air the addition of a radical scavenger stopped the reaction. The regeneration of PhPdOAc species from Ph 2 SbCl, HPdOAc species and oxygen is proposed as a key step in the catalytic cycle where oxygen-containing radical species might be present as intermediates.

Synthesis and structure of novel chiral oxazolinylferrocenes and oxazolinylferrocenylphosphines, and their rhodium(I)-complexes

A variety of chiral oxazolinylferrocenes are prepared from either ferrocenecarboxylic acid or cyanoferrocene and chiral β -amino alcohols. Highly diastereoselective ortho -lithiation (84 ≈ 99% de) of the oxazolinylferrocenes is accomplished with sec -butyllithium and the treatment of the lithiated compounds with an electrophile such as Mel, Ph 2 PCI or (PhSe) 2 gives the corresponding ortho -substituted oxazolinylferrocenes. The molecular structure of ( S , S )[2-(4′-isopropyloxazolin-2′-yl)ferrocenyl]diphenylphosphine ( 10 ), ( S , S )-2-phenyl-seleno-1-(4′-isopropyloxazolinyl)ferrecene ( 17 ), ( S , R )-3-methyl-1-diphenylphosphino-2-(4′-isopropyloxazolinyl)ferrocene ( 18 ), and ( S,S,S )-[2-(4′5′-diphenyloxazolin-2′-yl)ferrocenyl]diphenylphosphine (( S,S,S )-DIPOF; 21 ) has been fully characterized by X-ray crystal-lography. In connection with their usefulness as chiral ligands for Rh(I)-catalyzed asymmetric hydrosilylation of ketones, the square planar transition metal complexes having oxazolinylferrocenylphosphines, such as [Rh(COD)(P-N)]BF 4 and Rh(CO)(P-N)Cl (P-N = 10 or 21 ), are prepared by treatment of [Rh(COD) 2 ]BF 4 and [Rh(CO) 2 Cl] 2 with 10 and 21 , respectively, and all structures have been characterized spectroscopically and further confirmed by X-ray crystallography.

Highly fluorescent BODIPY dyes modulated with spirofluorene moieties.

A new type of structurally rigid BODIPY dye having spirofluorene moieties has been synthesized. These structurally constrained BODIPY dyes with spirofluorene moieties exhibit an intense bathochromic fluorescence. The solvent dependence of fluorescence ON/OFF switching of a BODIPY dye having an amino moiety was observed.

Ring-opening metathesis polymerization-based synthesis of polymeric nanoparticles for enhanced tumor imaging in vivo: Synergistic effect of folate-receptor targeting and PEGylation.

We have synthesized amphiphilic copolymers using ring-opening metathesis polymerization (ROMP), a copper-catalyzed dipolar click reaction, and osmium-catalyzed dihydroxylation. The resulting copolymers were easily conjugated with folate and dye (indocyanine green) moieties, using a transamidation method. The copolymers exhibited high water solubility and formed nanometer-sized self-assemblies in aqueous medium. The amphiphilic copolymers modified by dihydroxylation of the polymer backbone exhibited much lower cmc values than the non dihydroxylated copolymer. Copolymers conjugated with folate moieties reduced the fluorescence intensity of aqueous polymer solutions both in vitro and in vivo, but their self-assemblies efficiently accumulated at tumor sites because of folate-receptor recognition at tumor tissue. The PEGylation of copolymers improved the stability of the self-assemblies in aqueous medium as well as the tumor site selectivity in vivo. Furthermore, the fluorescent nanoparticles consisting of PEG- and folate-conjugated ROMP-based copolymers accumulated in tumor tissue selectively and efficiently, whereas accumulation in all other normal organs was reduced. The PEGylation and folate conjugation can synergistically improve the in vivo tumor site selectivity of ROMP-based copolymers.

Synthesis of 2-pyranylidene or (2-furyl)carbene–chromium complexes from conjugated enyne carbonyl compounds with Cr(CO)5(THF)

Abstract The reaction of β-ethynyl α,β-unsaturated esters or amides with Cr(CO) 5 (L) (L=Et 2 O, THF), derived from chromium hexacarbonyl, gives 2-pyranylidene–chromium complexes in good yields. The conjugated ene-carbonyl-vinylidene complex is a key intermediate to these Fischer-type oxacarbene complexes. In contrast, β-ethynyl α,β-unsaturated ketones react with Cr(CO) 5 (THF) to give (2-furyl)carbene complexes via nucleophilic attack of the carbonyl oxygen atom to the intermediate π-alkyne–chromium complexes. Some chemical transformation, such as [4+2] type cyclization of 2-pyranylidene complexes with alkynes and aldehyde formation from (2-furyl)carbene complexes, has also been described.

Practical synthesis of aromatic nitriles via gallium-catalysed electrophilic cyanation of aromatic C-H bonds.

A gallium-catalysed, direct cyanation reaction of aromatic and heteroaromatic C-H bonds with cyanogen bromide was developed as a practical synthetic method for the preparation of aromatic nitriles.

High‐Contrast Fluorescence Imaging of Tumors In Vivo Using Nanoparticles of Amphiphilic Brush‐Like Copolymers Produced by ROMP

Optical imaging techniques used to detect malignant tumors by endoscopy or at surgery require near-infrared fluorescence (NIRF) probes containing dyes with high signal-to-noise (S/ N) ratios. Along with a high S/N ratio in the near-infrared spectral region, these probes must accumulate specifically in the targeted tumor tissues. Spherical amphiphilic assemblies with diameters of 50–200 nm, such as liposomes, liposomelike assemblies, and micelles or vesicles of polymer conjugates, have been investigated with the expectation that they accumulate in solid tumors because of their enhanced permeability and retention (EPR) effect. Optical tumor imaging faces two problems. The first problem is the stability of the self-assembled amphiphilic copolymers. The disassembly of amphiphiles under diluted conditions, especially in blood vessels, reduces both their S/N ratio and specificity as probes for tumors. The second problem concerns the fluorescence intensities. Hydrophobic dyes attached to copolymers are prone to aggregate in aqueous solution, and self-quenching therefore reduces the quantum yields. To address the first problem, we focused our attention on the cross-linked assemblies of copolymers with hydrophobic and hydrophilic polymeric side chains (Figure 1). Because the polymer backbone bearing hydro-