Yoshinari Sawama

Concise asymmetric synthesis of a model compound, (4S,5S,6S)-6-(2,2-dimethoxy)ethyl-4,5-epoxy-6-hydroxy-2-cyclohexenone, for the cyclohexenone core of scyphostatin

Abstract The optically pure cyclohexenone core of scyphostatin ( 1 ) has been synthesized from cyclohexadiene acetal 5 . The crucial aspects of our synthesis include the intramolecular bromoetherification of 5 , the SeO 2 oxidation of 7 , and the enone formation of 13 to 4 in the final step.

Carbon–Carbon Bond Formation by Ligand‐free Cross‐Coupling Reaction Using Palladium Catalyst Supported on Synthetic Adsorbent

A palladium catalyst supported on a commercial synthetic adsorbent, DIAION HP20, could be employed for the crosscoupling reactions of aryl halides with organoboronic acids (Suzuki–Miyaura reaction), alkenes (Mizoroki–Heck reaction), and alkynes (Sonogashira reaction) in a ligand‐free manner. 10 % Pd/HP20 was highly active as the catalyst at approximately the same level as 10 % palladium on carbon (10 % Pd/C) for many of the reactions, and was especially effective for the Suzuki–Miyaura reaction using bromoaniline derivatives without the N‐protection and Sonogashira reaction of the heteroaryl iodides. As a stable supply and certain quality of HP20 are available as an industrial product, 10 % Pd/HP20 would be in practical use for a variety of cross‐coupling reactions and hydrogenation as the substitute for 10 % Pd/C, which is dependent on charcoal as a natural product.

Method for regio-, chemo- and stereoselective deuterium labeling of sugars based on ruthenium-catalyzed C-H bond activation.

An efficient and facile deuterium labeling of sugars has been achieved in a completely regio-, chemo- and stereoselective manner using the Ru/C-H(2)-D(2)O combination via C-H bond activation assisted by the coordination of Ru to the oxygen atom of the sugar-hydroxyl groups.

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.

Highly Regioselective Gold-Catalyzed Ring-Opening Allylation and Azidation of Dihydrofurans

The ring-opening allylation and azidation of 2,5-dihydrofurans has been accomplished with allyltrimethylsilane or Me(3)SiN(3) in the presence of catalytic amounts of HAuCl(4) x 3 H(2)O. Whereas the allylation proceeds regioselectively in the 2-position to afford 2,6-dien-1-ols, the azidation takes place in the 4-position exclusively.

Solvent-free Huisgen cyclization using heterogeneous copper catalysts supported on chelate resins

Copper catalysts supported on chelate resins bearing iminodiacetate moieties (DIAION CR11) or polyamine moieties (DIAION CR20) as chelating functional groups (12% Cu/CR11 and 7% Cu/CR20, respectively) were developed. 12% Cu/CR11 effectively catalyzed the Huisgen cycloaddition of mono-substituted alkynes to azides in the presence of triethylamine under totally solvent-free conditions to afford the corresponding 1,4-disubstituted 1,2,3-triazoles in excellent yields and in a completely regioselective manner. Furthermore, the Huisgen cycloaddition was found to effectively proceed without addition of triethylamine by the use of 7% Pd/CR20 as a catalyst.

Iron-catalyzed Friedel-Crafts benzylation with benzyl TMS ethers at room temperature.

Friedel-Crafts benzylations between unactivated arenes and benzyl alcohol derivatives are clean and straightforward processes to construct biologically useful di- and tri-arylmethanes. We have established an efficient iron-catalyzed Friedel-Crafts benzylation method at room temperature that uses benzyl TMS ethers as substrates, which are poorly reactive under common nucleophilic substitution conditions. The reaction seems to progress through iron-catalyzed self-condensation of the benzyl TMS ether to the corresponding dibenzylic ether. The use of excess arene relative to benzyl TMS ether produced mono-benzylated arene (di- and tri-arylmethane products), whereas the use of excess benzyl TMS ether versus arene provided bis-benzylated arene (polyarylated products) in high yields and regioselectivities. In previous methods, the latter double Friedel-Crafts benzylations hardly proceed.

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.