Tomohiro Maegawa

Efficient and Practical Arene Hydrogenation by Heterogeneous Catalysts under Mild Conditions

An efficient and practical arene hydrogenation procedure based on the use of heterogeneous platinum group catalysts has been developed. Rh/C is the most effective catalyst for the hydrogenation of the aromatic ring, which can be conducted in iPrOH under neutral conditions and at ordinary to medium H(2) pressures (<10 atm). A variety of arenes such as alkylbenzenes, benzoic acids, pyridines, furans, are hydrogenated to the corresponding cyclohexyl and heterocyclic compounds in good to excellent yields. The use of Ru/C, less expensive than Rh/C, affords an effective and practical method for the hydrogenation of arenes including phenols. Both catalysts can be reused several times after simple filtration without any significant loss of catalytic activity.

Facile and Clean Oxidation of Alcohols in Water Using Hypervalent Iodine(III) Reagents

The facile and efficient oxidation of various alcohols such as benzylic alcohols, primary alcohols, secondary alcohols, and diols in water using the hypervalent iodine(III) reagent, iodosobenzene (PhI=O), with KBr is described. Electrospray ionization (ESI) mass spectrometric studies on the behavior of PhI=O-KBr in aqueous solution suggested that these reactions are induced by the formation of highly reactive iodine species [PhI(Br)nO –]. Further development to recyclable polymer-supported iodine(III) reagent extends the utility of this reaction to afford an environmentally benign method.

Ligand‐Free Sonogashira Coupling Reactions with Heterogeneous Pd/C as the Catalyst

A variety of aryl iodides were coupled with aromatic and aliphatic terminal alkynes to give the corresponding 1,2-disubstituted aromatic alkynes in good yields by using only 0.4 mol % of the heterogeneous 10 % Pd/C as the catalyst without a ligand, copper salt, or amine in an aqueous medium.

Mild and Efficient H/D Exchange of Alkanes Based on CH Activation Catalyzed by Rhodium on Charcoal

The C H bond activation of organic compounds is one of the most useful synthetic methods for the fuctionalization of simple molecules. The activation of unsaturated compounds can be achieved using transition-metal catalysts, and the coordination of a metal center to the p bond plays an important role in the reaction process. On the other hand, alkanes (saturated organic compounds) are known to be much less reactive towards C H bond activation than unsaturated compounds because alkanes possess no coordination sites for metals. Therefore only a few processes, such as oxidation, H/D exchange, dehydrogenation, and radical reactions, have been reported as being C H activationinduced, even though extensive efforts to activate alkanes have been made. The H/D exchange reaction is a basic transformation of alkanes. Deuterated products have received attention not only as useful tools for the investigation of human metabolism or reaction mechanisms, but also as functional materials like deuterated polymers as components of optical fibers for high-speed telecommunications systems. Deuterated pesticides and pharmaceuticals are also effective for quantitative analyses and bioanalytical investigations as internal standards, while deuterated alkanes are expected to be applied as marker molecules to prevent the distribution of illegally mixed light diesel oil. Owing to this increasing interest, it is important to develop an efficient and facile H/D exchange method for alkanes. Since the first H/D exchange of alkanes was reported by Shilov and co-workers, other H/D exchange reactions of alkanes have been developed. Recently, Bergman and co-workers reported an efficient H/D exchange method for various substrates, including alkanes, by using a homogeneous cationic Ir hydride complex under mild conditions. The H/D exchange reaction with deuterium oxide catalyzed by Pd/C under hydrothermal conditions has also been reported. We have recently established a method for deuterium incorporation into organic molecules by using a combination of Pd/C (or Pt/C) in D2O under H2, which has led to efficient H/D exchange for a variety of organic molecules such as aromatic compounds, ketones, and alcohols (Scheme 1). As part of an ongoing program for the development of H/D exchange reactions induced by heterogeneous catalysts, we have discovered a unique protocol for the C H

A simple and efficient oxidation of alcohols with ruthenium on carbon

A simple, efficient, and environmentally-friendly heterogeneous Ru/C-catalyzed oxidation of secondary and primary alcohols without additives under an atmosphere of oxygen has been established.

Novel and efficient oxidative biaryl coupling reaction of alkylarenes using a hypervalent iodine(III) reagent

Abstract First facile and efficient oxidative coupling reaction of alkylarenes leading to alkylbiaryls using a combination of hypervalent iodine(III) reagent, phenyliodine(III) bis(trifluoroacetate) (PIFA), and BF 3 ·Et 2 O has been developed.

Facile and Convenient Method of Deuterium Gas Generation Using a Pd/C‐Catalyzed H2–D2 Exchange Reaction and Its Application to Synthesis of Deuterium‐Labeled Compounds

The Pd/C-catalyzed H(2)-D(2) exchange reaction using a H(2)-D(2)O combination provided a general, efficient and environmentally friendly route for the preparation of deuterium gas (D(2)). H(2) sealed in a reaction flask was converted into nearly pure D(2), which could be used for the Pd/C-catalyzed one-pot reductive deuteration of various reducible functionalities and the chemoselective one-pot deuterogenation of olefin and acetylene. Additionally, we established the capturing method of the generated D(2) in a balloon, which was successfully applied to the Pd/C-catalyzed reductive mono-N-alkylation of a primary amine using nitrile as the alkylating reagent.

A Highly Active Heterogeneous Palladium Catalyst Supported on a Synthetic Adsorbent

Yasunari Monguchi, Yuki Fujita, Koichi Endo, Shinobu Takao, Masatoshi Yoshimura, Yukio Takagi, Tomohiro Maegawa, and Hironao Sajiki* Laboratory of Organic Chemistry, Gifu Pharmaceutical University 5-6-1 Mitahora-higashi, Gifu 502-8585, Japan N.E. Chemcat Corporation, 678 Ipponmatsu, Numazu, Shizuoka 410-0314, Japan Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamada-oka, Suita, Osaka, Japan e-mail: monguchi@gifu-pu.ac.jp, sajiki@gifu-pu.ac.jp

[Cu(OH)(TMEDA)]2Cl2-Catalyzed Regioselective 2-Arylation of 5-Substituted Tetrazoles with Boronic Acids under Mild Conditions

A mild and regioselective 2-arylation of 5-substituted tetrazoles is described. The reaction proceeds regioselectively with a variety of arylboronic acids in the presence of [Cu(OH)(TMEDA)]2Cl2 to afford 2,5-disubstituted tetrazoles. This is the first report of highly regioselective arylation of 5-alkyltetrazoles.

Reversing the Reactivity of Carbonyl Functions with Phosphonium Salts: Enantioselective Total Synthesis of (+)‐Centrolobine

The control of chemoselective transformations irrespective of the individual reactivity of functional groups still remains a largely unanswered challenge. Carbonyl groups, such as aldehydes and ketones, are without doubt the most important functional groups in organic chemistry and their reactions are well known. The order of the reactivity of carbonyl groups toward nucleophiles is generally aldehyde> ketone> ester. Therefore, it is easy to react an aldehyde in the presence of ketones and esters. In contrast, it is difficult to react a ketone prior to an aldehyde. Therefore, protective groups have to be employed for such transformations, which thus become intrusive three-step operations that involve the protection of the aldehyde, transformation of the ketone, and deprotection of the aldehyde. The reversal of the reactivity of functional groups is a challenging theme in chemistry and there are few reports on such transformations. Luche and Gemal reported pioneering and representative work, in which a ketone was selectively reduced in the presence of an aliphatic aldehyde. The conversion of the aldehyde into an acetal, the subsequent reduction of the ketone with NaBH4, and the deacetalization were carried out in one pot by using the CeCl3–MeOH–NaBH4 system. However, this reaction was limited to reductions and is difficult to apply to other reactions. Other methods, such as the use of metal amides, a bulky Lewis acid, and a copper catalyst with a bulky phosphine ligand, were reported. However, these methods have drawbacks, such as lower generality, the need to prepare special reagents, and strict control of stoichiometry because of the use of highly reactive reagents. Therefore, more practical and facile methods for the selective transformation of carbonyl groups are required. Herein we report the convenient and versatile selective one-pot transformation of less-reactive carbonyl groups in the presence of aldehydes (or ketones) by using the combination of PPh3 (or PEt3) and TMSOTf to selectively mask the aldehyde prior to the addition of the nucleophile (Scheme 1). The asymmetric transformation of a less-reactive carbonyl group in the presence of a more-reactive carbonyl group was also accomplished, and was applied to the short asymmetric total synthesis of (+)-centrolobine.