Naoyuki Hoshiya

Sulfur Modification of Au via Treatment with Piranha Solution Provides Low-Pd Releasing and Recyclable Pd Material, SAPd

We have found in the SR-HXPS measurement of Piranha-treated Au(111)/mica that the gold surface underwent sulfur modification during this treatment, which was believed to have only removed impurities from the gold surface. We also successfully developed a practical Pd material, SAPd, whose Pd was immobilized on sulfur-modified Au. With the lowest Pd-releasing levels and high recyclability, this is one of the best Pd materials thus far developed. Because it leaches extremely low levels of Pd into reaction mixtures, removal of the residual Pd is unnecessary using SAPd, even in syntheses involving pharmaceutical ingredients.

Palladium-Catalyzed Arylation of Cyclopropanes via Directing Group-Mediated C(sp3)–H Bond Activation To Construct Quaternary Carbon Centers: Synthesis of cis- and trans-1,1,2-Trisubstituted Chiral Cyclopropanes

Pd(II)-catalyzed tertiary C(sp(3))-H arylation of cyclopropanes via directing group-mediated C-H activation for the construction of a chiral quaternary carbon center on cyclopropanes using aryl iodides as a coupling partner is reported. The arylation had a wide substrate scope and good functional group tolerance, including heteroaryl iodides, to provide various chiral arylcyclopropanes with the cis- and trans-1,1,2-trisubstituted structures.

Palladium-Nanoparticle-Catalyzed 1,7-Palladium Migration Involving C–H Activation, Followed by Intramolecular Amination: Regioselective Synthesis of N1-Arylbenzotriazoles and an Evaluation of Their Inhibitory Activity toward Indoleamine 2,3-Dioxygenase

A sulfur-modified gold-supported palladium material (SAPd) has been developed bearing palladium nanoparticles on its surface. Herein, we report for the first time the use of SAPd to affect a Pd-nanoparticle-catalyzed 1,7-Pd migration reaction for the synthesis of benzotriazoles via C-H bond activation. The resulting benzotriazoles were evaluated in terms of their inhibitory activity toward indoleamine 2,3-dioxygenase.

Pd(II)-Catalyzed Alkylation of Tertiary Carbon via Directing-Group-Mediated C(sp3)–H Activation: Synthesis of Chiral 1,1,2-Trialkyl Substituted Cyclopropanes

A Pd(OAc)2-catalyzed alkylation reaction of the tertiary carbon of chiral cyclopropane substrates with alkyl iodides and bromides via C(sp(3))-H activation has been developed. This is an elusive example of a C-H activation-mediated alkylation of tertiary carbon to effectively construct a quaternary carbon center. The alkylation proceeded with various alkyl halides, including those of functional groups, to provide a variety of chiral cis- and trans-1,1,2,-trialkyl substituted cyclopropanes of medicinal chemical importance.

Suzuki–Miyaura cross-coupling reactions using a low-leaching and highly recyclable gold-supported palladium material and two types of microwave equipments

We designed Suzuki–Miyaura cross-coupling reactions in conjunction with sulfur-modified Au-supported Pd material (SAPd) and two types of microwaves, single-mode and multi-mode. The entire microwave-facilitated process provided advantages over conventional heating in that reactivity of the less reactive arylbromides was induced and the reaction time was reduced.

Development of a Recyclable and Low-Leaching Palladium Catalyst Supported on Sulfur-Modified Gallium Arsenide (001) for Use in Suzuki–Miyaura Coupling

A newly developed, environmentally benign palladium catalyst supported on gallium arsenide, {Pd}‐S‐GaAs(001), has both the lowest recorded leaching and high recyclability for Suzuki–Miyaura coupling. Measurements of the catalyst surface by synchrotron radiation X‐ray photoelectron spectroscopy show a relationship between the surface and the activity of the catalyst. Since {Pd}‐S‐GaAs(001) makes efficient use of the rare metal Pd, it is a useful palladium catalyst from an atom‐ economical perspective. Two heterogeneity tests clarify that the presence of immobilized palladium on SGaAs is important for higher catalytic activity.

Double carbonylation of aryl iodides with amines under an atmospheric pressure of carbon monoxide using sulfur-modified Au-supported palladium

A double carbonylation of aryl iodides with amines proceeded smoothly under an atmospheric pressure of carbon monoxide by using palladium nanoparticles (Pd NPs) leached from a sulfur-modified Au-supported palladium material (SAPd), producing α-ketoamides in good to excellent yields.

Construction of Iterative Tetrahydrofuran Ring Units and Total Synthesis of (+)-Goniocin

Cytotoxic acetogenin (+)-goniocin has been synthesized in 17 steps from (R)-O-tritylglycidol. The core structure of the contiguous C22-C10 threo-trans-threo-trans-threo-trans-tris-tetrahydrofuran (THF) ring involving an iterative THF-ring unit was synthesized. An iterative THF ring unit was constructed from an alkenyl-substituted THF ring in four steps including a Pd(II)-catalyzed ring-closing reaction and cross-metathesis. This method is general and allows the preparation of both trans-threo-trans- and trans-threo-cis-THF ring units flexibly.

Hard x-ray photoemission spectroscopic investigation of palladium catalysts immobilized on a GaAs(001) surface

We present studies on the structure and chemical states of a catalyst developed by immobilizing palladium on S-terminated GaAs(001). Hard x-ray photoelectron spectroscopy (HX-PES) of core-level and valence band photoemission consistently indicates that the organopalladium molecules are reduced on the surface yielding Pd nanoparticles with a metallic nature. This finding is supported by high-resolution observations using scanning electron microscopy and backscattered electron image. HX-PES results also reveal that a portion of S atoms forming the S-termination is oxidized during the formation of Pd nanoparticles.

Formation of self-assembled multi-layer stable palladium nanoparticles for ligand-free coupling reactions

The structure of a recently developed Pd catalyst, named sulfur-modified gold-supported palladium (SAPd), has been determined to be composed of multi-layered Pd nanoparticles. SAPd is easily prepared by self-assembly on a sulfur-modified gold surface, and near-edge X-ray absorption fine structure (NEXAFS) analysis at the Pd K-edge determined that the Pd in SAPd is zero-valence analogous to metallic Pd. However, transmission electron microscopy (TEM) analyses and extended X-ray absorption fine structure (EXAFS) analysis clarified that SAPd has approximately 10 layers and consists of nanoparticles with a diameter less than 5 nm. High-density Pd nanoparticles were embedded without condensation. NEXAFS analysis at the S and C K-edge revealed that the organic matter containing sulfate and xylene as a major ingredient is distributed between Pd nanoparticles, and it seems to prevent condensation. These findings suggest that a highly efficient cross-coupling reaction, which was reported in earlier works, has been achieved by the high-density Pd nanoparticles.