Reuse of chiral ruthenium catalyst in catalytic asymmetric transfer hydrogenation (CATH) has attracted attention from economic and environmental viewpoints, and reactions using ionic liquids (ILs) as solvent are recognized as one of the most useful methods for reuse of the catalyst. We synthesized (1S,2S)-N-(p-toluenesulfonyl)-1,2-diphenylethylenediamine (TsDPEN) derivatives with various ionic moieties, and investigated the effect of their structure with respect to catalytic ability and recyclability in CATH with ILs. Ligand 3a having an imidazolium group showed the best results, and significant differences were observed depending on the structure of the ionic moiety or the length of the alkyl chain connecting the ligand site and the ionic moiety. Among various prochiral ketones used as substrates at various cycles, 3a showed a relatively good result.Key words ionic liquid; recyclable catalytic asymmetric hydrogenation; task-specific ligand; imidazolium salt Catalytic asymmetric transfer hydrogenation (CATH) is a very useful method for obtaining optically active secondary alcohols from prochiral ketones and for serving as an alternative to catalytic asymmetric hydrogenation with molecular hydrogen. CATH has many advantages in terms of safety and convenience over conventional hydrogenation because it uses 2-propanol or formic acid as a hydrogen source.1,2) Similar to catalytic asymmetric hydrogenation, CATH can also proceed with high catalytic efficiency and enantioselectivity by using a chiral transition metal complex. Especially well known as a catalyst is the ruthenium complex (1 and 2) with chiral N-(p-toluenesulfonyl)-1,2-diphenylethylenediamine (TsDPEN) reported by Noyori and colleagues.3-5) CATH with the ruthenium catalyst has a high degree of applicability for synthetic chemistry in the laboratory as well as in industry. Several attempts to use CATH with recyclable catalysts have been reported with the aim of industrial application. The reuse of expensive transition metals such as ruthenium and the reduction of waste from reactions is advantageous from economic and environmental viewpoints. Indeed, transfer hydrogenation using polymer-or dendritic-supported TsDPEN ligand under heterogeneous conditions has been reported. [6][7][8][9][10][11][12][13] Serving as a new type of solvent for green technology are ionic liquids (ILs), which consist of ions such as quaternary ammonium or phosphonium ions and are liquids at room temperature.14-18) Although the toxicity and biodegradability of ILs have not been sufficiently explored, they are known to be non-volatile and non-flammable.14-19) Therefore, the use of ILs offers safety and environmental protection, as well as eliminates the problem of volatilization loss, which occurs with conventional organic solvents. In addition, ILs have the ability to dissolve organic and inorganic compounds, while being immiscible with less polar solvent and water. Organometallic complexes can work as homogeneous catalysts in ILs, and a simple extraction procedure can separate the p...

The oxidation of (Z)-1,2-bis(arylseleno)-1-alkenes is known to afford alkynyl selenoxides via a unique selenoxide anti-elimination mechanism; however, to date, there have been no mechanistic studies of this reaction. During our studies of this transformation, monoselenoxides 6 and 7 were unexpectedly isolated as stable reaction intermediates. In addition, (77)Se NMR studies of the reaction mixture revealed the presence of an intramolecular Se···O interaction and the formation of alkynyl selenoxides. Meanwhile, even at higher temperatures, the reaction of a (Z)-1,2-bis(arylsulfinyl)-1-alkene, the sulfur analog of (Z)-1,2-bis(arylseleninyl)-1-alkenes, did not proceed via sulfoxide elimination but proceeded via isomerization and disproportionation. Therefore, the intramolecular Se···O interaction can be concluded to play a pivotal role in the anti-elimination reaction.

We synthesize optically active (R)-terbutaline 2, which is an anti-asthmatic drug, through recyclable catalytic asymmetric transfer hydrogenation (RCATH). Various chloroketones 4 were prepared and RCATH was performed on them. The products exhibit moderate to high enantioselectivity. In particular, the hydrogenation of acyl substituted substrates 4c yields chiral secondary alcohols 5c in good yield and enantioselectivity. Furthermore, (R)-terbutaline 2 can be synthesized in one step from the resulting secondary alcohol 5 without racemization.Key words chiral ligand; ionic liquid; recyclable catalytic asymmetric transfer hydrogenation; terbutaline Ionic liquids are ionic compounds that have the liquid form at temperatures below 100°C, or even at room temperature. They are non-volatile and non-flammable. Moreover, they exhibit (1) stability for reaction reagents such as acids or bases; (2) solubility for organic, inorganic, and metal compounds; and (3) recyclability after a work-up process. Ionic liquids have been attracting attention recently as environmentally friendly solvents.1-4) For example, an asymmetric acylation of an allylic alcohol using an enzymatic reaction in an ionic liquid has been reported 5) as well as a reaction system in which the ion liquid can be repeatedly used as a catalyst container, with high catalyst activity, and as a reaction solvent. 6)Catalytic transfer hydrogenation (CTH) is a reduction reaction involving the exchange of hydrogen atoms between organic compounds such as 2-propanol or formic acid in the presence of catalysis agents. [7][8][9] It has several advantages such as (1) the absence of an explosive or flammable hydrogen source, (2) mild reaction conditions, and (3) avoidance of harmful by-products. Catalytic asymmetric transfer hydrogenation (CATH), in particular, is a very useful method for obtaining optically active secondary alcohols from prochiral ketones. CATH has many advantages in terms of safety and convenience over conventional hydrogenation because it uses 2-propanol or formic acid as a hydrogen source. 10,11) In previous work, we showed that recyclable CATH (RCATH) can be performed in an ionic liquid [bmim] [PF 6 ] using an ionic chiral ligand and the Ru(II) catalyst. We prepared several types of ionic ligands, including pyridinium, benzimidazolium, or imidazolium derivatives. Furthermore, by examining the length of the carbon chains and an imidazolium part, we developed chiral ligand 1, which was most suitable for RCATH 12,13) (Fig. 1). Because they can recycle a catalyst and a reaction solvent in RCATH, optically active organic compounds and pharmaceutical products can be synthesized by this method that is inexpensive and environmentally benign.The β-agonist, which is used as a catecholamine-related pharmaceutical drug for asthma treatment, is generally used in the racemic form, although its pharmacologically active compounds are (R)-isomers in many cases (for example, terbutaline 2 and salbutamol 3). 14-18) Terbutaline 2 is used in the racemic form in clinical p...

A highly regio-and stereoselective selenoxide elimination of 1,2-bis [4-(trimethylsilyl)phenylseleno]alkanes to give (E)-alkenyl selenoxides and its mechanistic studyThe elimination of a 2-substituted selenoxide is known to provide a variety of different products, which are largely dependent on the nature of the substrate and its substituents. Oxidation of (Z)-1,2-bisarylseleno-1-alkenes lead to formation of bisselenoxide intermediate, which gives the corresponding alkynyl selenide by anti-elimination and subsequent reduction by the ArSeOH byproduct. In this study, the selective elimination of selenoxide from 1,2-bis[4-(trimethylsilyl)phenylseleno]alkanes resulted in the exclusive formation of (E)-alkenyl selenoxides via a 1,2-bisselenoxide intermediate. The oxidation of 1,2-bis[4-(trimethylsilyl)phenylseleno]alkanes with one equivalent of metachloroperoxybenzoic acid resulted in the non-selective formation of several arylseleno alkene derivatives, and it was subsequently shown that the elimination of the corresponding 1,2bisselenoxide proceeds with high regio-and stereoselectivity. Mechanistic investigations for this unique elimination have been performed with 77 Se NMR experiments and computational studies.the corresponding allylic product. [3][4][5] The failure of this strategy for the synthesis of enol derivatives from 2-oxygen-substituted selenides has already been reported. This phenomenon was at- [a] A.