Efficient h/d exchange reactions of alkyl-substituted benzene derivatives by means of the Pd/C-H(2)-D(2)O system

A method for efficient and extensive H/D exchange of substituted benzene derivatives which is catalyzed by heterogeneous Pd/C in D(2)O as a deuterium source under hydrogen atmosphere is described. Multi-deuterium incorporation into unactivated linear or branched alkyl chains that bear a carboxyl, hydroxyl, ether, ester, or amide moiety and are connected with a benzene ring was achieved by using the Pd/C-H(2)-D(2)O system. The present method does not require expensive deuterium gas or any special equipment.     

Effect of associating polymer on the viscosity behavior of suspensions consisting of particles with different surface properties

Associating polymers which consist of water-soluble long-chain molecules containing a small fraction of hydrophobic groups (hydrophobes) behave as flocculants in aqueous suspensions. The effects of associating polymers on the rheological behavior are studied for single suspensions of particles with hydrophilic and hydrophobic surfaces, and their mixtures. For particles with hydrophilic surfaces, the suspensions are highly flocculated by a bridging mechanism, because the water-soluble chains adsorb onto hydrophilic surfaces. On the other hand, the particles with hydrophobic surfaces cannot be dispersed in water without polymer and the additions of a small amount of polymer are required for preparation of homogeneous suspensions. The associating polymer acts as a dispersant at low concentrations. However, further additions of polymer lead to a drastic increase in viscosity. Since the hydrophobes on one end of molecules adsorb onto hydrophobic surfaces and other hydrophobes tending from the particles can form micelles, the particles are connected by linkage of interchain associations. By mixing two suspensions of particles with hydrophilic and hydrophobic surfaces, the viscosity is substantially reduced and the flow becomes nearly Newtonian. The associating polymer in complex suspensions acts as a binder between the hydrophilic and hydrophobic surfaces. The hetero-flocculation which leads to the formation of composite particles may be responsible for the viscosity reduction of complex suspensions.     

Stereo‐ and Regioselective Direct Multi‐Deuterium‐Labeling Methods for Sugars

Deuterium‐labeled sugars can be utilized as powerful tools for the architectural analyses of high‐sugar‐containing molecules represented by the nucleic acids and glycoproteins, and chiral building blocks for the syntheses of new drug candidates (heavy drugs) due to their potential characteristics, such as simplifying the ¹H NMR spectra and the stability of C? D bonds compared with C? H bonds. We have established a direct and efficient synthetic method of deuterated sugars from non‐labeled sugars by using the heterogeneous Ru/C‐catalyzed H–D exchange reaction in D₂O under a hydrogen atmosphere with perfect chemo‐ and stereoselectivities. The direct H–D exchange reaction can selectively proceed on carbons adjacent to the free hydroxyl groups, and the deuterium labeling of various pyranosides (such as glucose and disaccharides), as well as furanosides, represented by ribose and deoxyribose was realized. Furthermore, the desired number of deuterium atoms can be freely incorporated into selected positions by the site‐selective protection of the hydroxyl groups using acetal‐type protective groups because the deuterium exchange reaction never proceeds on positions adjacent to the protected hydroxyl groups.     

One-pot aromatic amination based on carbon–nitrogen coupling reaction between aryl halides and azido compounds

An efficient copper-mediated C–N coupling reaction between various aryl halides and azido compounds to produce the corresponding aromatic primary amines was established. The present amination is apparently involved in both the reduction of an azido functionality to the corresponding primary amino group and its cross-coupling reaction with aryl halides in a one-pot manner. The present amination could be applied to the synthesis of procaine, a local anesthetic drug. A mechanistic study indicated that 2-aminoethanol could work as a major hydrogen donor and the reaction would proceed without the formation of the intermediary aryl azide.     

Absolute structure of shoreaketone: a rotational isomeric resveratrol tetramer in Dipterocarpaceaeous plants

A rotational isomeric shoreaketone (1), identified as a skeletal member of resveratrol tetramers, was isolated from three species of Dipterocarpaceaeous plants: Shorea uliginosa, Shorea hemsleyana, and Vateria indica. The structure was elucidated by spectroscopic analysis including NMR experiments and their absolute configurations determined based on circular dichroism data. Shoreaketone has 10 asymmetric carbons and a framework of fused heptacyclic ring system including a spiro ring and an α,β-unsaturated carbonyl group that has not been reported in any other natural product. NMR experiments using shoreaketone indicate the presence of two conformers due to restricted rotation of a C–C bond in solution. The complex stereochemistry is due to its skeleton, 10 asymmetric carbons, and a chiral axis. The conformations of rotational isomeric stilbenoid were studied by variable-temperature NMR, ROESY, a skeletal conversion. The coexistence of two conformers for shoreaketone (1) was confirmed to be 1a and 1b, in which the diaryl-dihydrobenzofuran moiety (unit 1B) is extended below or above the plane of the cyclopentane ring (unit 1A), respectively.     

Aromatic ring favorable and efficient H-D exchange reaction catalyzed by Pt/C

An effective and applicable Pt/C-catalyzed deuteration method of aromatic rings using D₂O as a deuterium source under hydrogen atmosphere was developed. Five percent Pt/C would lead to quite effective H-D exchange results on the aromatic ring systems. The reaction is general for a variety of aromatic compounds including biologically active compounds.     

The structure of paraherquamide,a toxic metabolite from penicilliumparaherquei

A new toxic metabolite was isolated from $\text{Penicillium}$$\text{paraherquei}$ and the structure was determined by X-ray diffraction analysis. The metabolite was designated as paraherquamide.     

Rearrangement of allylic azide and phenylthio groups of 3′-azido- or 3′-phenylthio-4′,5′-didehydro-5′-deoxyarabinofuranosyluridines

The reversible intramolecular [3,3]-sigmatropic rearrangement between 1-(3-azido-3,5-dideoxy-β-d-threo-pent-4-enofuranosyl)uracil (3) and 1-(5-azido-3,5-dideoxy-β-d-glycero-pent-4-enofuranosyl)uracil (4) and irreversible radical rearrangement of 1-(3,5-dideoxy-3-phenylthio-β-d-threo-pent-4-enofuranosyl)uracil (5) and 1-[3,5-dideoxy-3-(4-tolyl)thio-β-d-threo-pent-4-enofuranosyl]uracil (7) into 1-(3,5-dideoxy-5-phenylthio-β-l-glycero-pent-4-enofuranosyl)uracil (6) and 1-[3,5-dideoxy-5-(4-tolyl)thio-β-l-glycero-pent-3-enofuranosyl]uracil (8) were attained at room temperature.     

Continuous‐Flow Suzuki‐Miyaura and Mizoroki‐Heck Reactions under Microwave Heating Conditions

Microwave‐assisted continuous‐flow reactions have attracted significant interest from synthetic organic chemists, especially process chemists from practical points of view, due to a less complicated shift to large‐scale synthesis based on simple and continuous access to products with low energy requirements. In this personal account, we focused on the Suzuki‐Miyaura and Mizoroki‐Heck reactions, both of which are significantly important cross‐coupling reactions for the synthesis of various functional materials. Microwave power is effective for heating. Typical homogeneous palladium catalysts, such as PdCl₂(PPh₃)₂, Pd(PPh₃)₄, and Pd(OAc)₂, as well as heterogeneous palladium catalysts, such as Pd‐film, Pd/Al₂O₃, Pd/SiO₂, and Pd supported on polymers, can be used for these reactions.     

Pd/C(en) catalyzed chemoselective hydrogenation in the presence of aryl nitriles

Aromatic nitriles are not only important components of natural products, pharmaceuticals, herbicides and agrochemicals but also a synthetic equivalent of various functionalities. The development of synthetic methods of aromatic nitriles have been increasing in terms of its usefulness. Since aromatic nitriles are susceptible to the hydrogenation, it has been desired for the development of chemoselective hydrogenation method with retention of nitrile groups. Pd/C is one of the most popular catalysts for hydrogenation and many of reducible functional groups such as multiple bonds, benzyl ethers, N-Cbzs, nitro groups and so on could be easily reduced under the conditions. Therefore, it is very difficult to achieve the chemoselective hydrogenation of substrates containing two or more reducible functional groups. We have found that a Pd/C catalyst formed an isolable complex with ethylenediamine (en) employed as catalytic poison, and the complex [Pd/C(en)] catalyzed chemoselective hydrogenation of a variety of reducible functionalities distinguishing O-benzyl, N-Cbz and O-TBDMS protective groups, benzyl alcohols and epoxides. In the course of these investigations, we found the aryl nitriles could survive under the Pd/C(en)-catalyzed hydrogenation conditions in THF whose choice is important for the effective suppression. This methodology could be applied to the selective hydrogenation of alkene and alkyne functionalities in the presence of aromatic nitrile.