Yuki Yabe

Rhodium-on-carbon catalyzed hydrogen scavenger- and oxidant-free dehydrogenation of alcohols in aqueous media

The efficient and catalytic dehydrogenation of alcohols is a clean approach for preparing carbonyl compounds accompanied only by the generation of hydrogen gas. We have accomplished the heterogeneous rhodium-on-carbon catalyzed dehydrogenation of secondary, as well as primary, alcohols to the corresponding ketones and carboxylic acids in water under basic conditions.

New aspect of chemoselective hydrogenation utilizing heterogeneous palladium catalysts supported by nitrogen- and oxygen-containing macromolecules

Heterogeneous palladium catalysts supported on nitrogen-containing macromolecules, such as fibroin (Fib), polyethyleneimine (PEI), boron nitride (BN), and molecular sieves (MS), oxygen-containing macromolecules were developed. The Pd/Fib, Pd/PEI, Pd/BN, Pd/MS3A and Pd/MS5A were used for the novel chemoselective hydrogenation of the reducible functionalities. These catalysts were easy to handle and easily prepared by stirring a macromolecule-suspended palladium diacetate solution in methanol at room temperature. The absorption effect of the Pd species to the macromolecules and the catalyst activity were partially controlled by the lone pairs of the nitrogen atoms in the macromolecule. Pd/Fib, Pd/MS or Pd/BN mainly enabled the chemoselective hydrogenation of azide, alkene and alkyne in the presence of other reducible functionalities. Furthermore, the chemoselective semi-hydrogenation of alkynes to alkenes could be achieved using Pd/PEI or Pd/BN with a nitrogen-containing base catalyst.

Iron-Catalyzed Chemoselective Azidation of Benzylic Silyl Ethers

Azidation: siloxy groups derived from secondary and tertiary benzyl alcohols can be transformed into azide groups at room temperature using TMSN(3) in the presence of an iron catalyst (TMS=trimethylsilyl). Secondary and tertiary benzylic silyl ethers can be transformed in the presence of primary silyl ethers, and other reactive functional groups, such as alkyl chlorides, α,β-unsaturated esters, and aldehydes, are stable under the reaction conditions.

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 (1)H 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 D(2)O 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.

Easily‐Controlled Chemoselective Hydrogenation by using Palladium on Boron Nitride

The hydrogenation catalyzed heterogeneously by palladium on boron nitride (Pd/BN) in methanol realized the chemoselective hydrogenation of only azides, alkenes, and alkynes in the presence of other reducible functionalities such as benzyl ethers, aryl halides, aryl ketones, and nitro groups. Furthermore, the totally chemoselective semihydrogenation of alkynes could also be achieved without the reduction of other coexisting reducible functionalities, which include azides and alkenes, by using Pd/BN in pyridine as a solvent.

Chemoselective hydrogenation reaction of unsaturated bonds in the presence of an o-nitrobenzenesulfonyl group.

Chemoselective hydrogenation of unsaturated compounds bearing an o-nitrobenzenesulfonyl (Ns)-amide moiety, affording the corresponding saturated compounds, was accomplished efficiently without loss of the nitro group by using the Pd/MS3A catalyst and a H2 balloon. Partial hydrogenation of alkynes bearing an Ns group to corresponding cis alkenes was achieved with the combination of the Pd/BN catalyst and an additive (diethylenetriamine or acetic acid).

DIBAL-mediated reductive transformation of trans-dimethyl tartrate acetonide into ε-hydroxy α,β-unsaturated ester and its derivatives.

Stepwise, selective DIBAL reduction of the acetonide diester derived from tartaric acid followed by the Horner-Emmons reaction effectively provided desymmetrized hydroxy mono-olefination products in a one-pot operation.

Stainless‐Steel Ball‐Milling Method for Hydro‐/Deutero‐genation using H2O/D2O as a Hydrogen/Deuterium Source

A one-pot continuous-flow method for hydrogen (deuterium) generation and subsequent hydrogenation (deuterogenation) was developed using a stainless-steel (SUS304)-mediated ball-milling approach. SUS304, especially zero-valent Cr and Ni as constituents of the SUS304, and mechanochemical processing played crucial roles in the development of the reactions.

Gold-Catalyzed Benzylic Azidation of Phthalans and Isochromans and Subsequent FeCl3-Catalyzed Nucleophilic Substitutions

The benzylic positions of the phthalan and isochroman derivatives (1) as benzene-fused cyclic ethers effectively underwent gold-catalyzed direct azidation using trimethylsilylazide (TMSN3) to give the corresponding 1-azidated products (2) possessing the N,O-acetal partial structure. The azido group of the N,O-acetal behaved as a leaving group in the presence of catalytic iron(III) chloride, and 1-aryl or allyl phthalan and isochroman derivatives were obtained by nucleophilic arylation or allylation, respectively. Meanwhile, a double nucleophilic substitution toward the 1-azidated products (2) occurred at the 1-position using indole derivatives as a nucleophile accompanied by elimination of the azido group and subsequent ring opening of the cyclic ether nucleus produced the bisindolylarylmethane derivatives.