A New Class of Tunable Dendritic Diphosphine Ligands: Synthesis and Applications in the Ru-Catalyzed Asymmetric Hydrogenation of Functionalized Ketones

Cinchona-Alkaloid-Derived NNP Ligand for Iridium-Catalyzed Asymmetric Hydrogenation of β-Keto Ester

The Ir-catalyzed asymmetric hydrogenation of β-keto esters with Cinchona-alkaloid-derived NNP ligands has been developed. β-Hydroxy esters of opposite configuration were afforded smoothly with 91.5-99.1 and 81.6-99.3% ee, respectively, using NNP L2 and L7 derived from quinidine and quinine separately even on the gram scale. The protocol for the preparation of β-hydroxy esters of opposite configuration by the simple conversion of ligand configurations offered further opportunities for the synthesis of biologically active molecules and drugs.

Fluorine-Assisted Rearrangement of Geminal Azidofluorides to Imidoyl Fluorides

Organoazide rearrangement constitutes versatile synthetic strategies but typically requires an extremely strong acid and/or a high reaction temperature. Our group recently discovered the remarkable accelerating effect of the geminal fluorine substituent that enables the facile rearrangement of azides into imidoyl fluorides without the aid of acid under much milder reaction conditions. The role of geminal fluorine was elucidated by both experimental and computational investigations. This new reactivity led to the development of a practical one-step tandem preparative method for potentially useful and bench-stable imidoyl fluorides from a wide range of structurally diverse geminal chlorofluorides. Our additional efforts to expand the reaction scope regarding the migrating group, halogen, and carbonyl function are described, and the synthetic utility of the imidoyl fluoride products was demonstrated in hopes of promoting the use of this under-appreciated functional group in the synthetic organic community.

Visible-light enabled photochemical reduction of 1,2-dicarbonyl compounds by Hünig's base

A visible-light enabled, chemoselective photoreduction of 1,2-dicarbonyl compounds by using Hünig's base as reductant is reported.

Asymmetric Transfer Hydrogenation of α-Keto Amides; Highly Enantioselective Formation of Malic Acid Diamides and α-Hydroxyamides

The asymmetric transfer hydrogenation (ATH) of α-keto-1,4-diamides using a tethered Ru/TsDPEN catalyst was achieved in high ee. Studies on derivatives identified the structural elements which lead to the highest enantioselectivities in the products. The α-keto-amide reduction products have been converted to a range of synthetically valuable derivatives.

Ni(II)-Catalyzed Enantioselective Synthesis of β-Hydroxy Esters with Carboxylate Assistance

A Ni-oxazoline complex-catalyzed asymmetric decarboxylative aldol reaction between malonic acid half-oxyesters and various carbonyls with carboxylate assistance was developed, affording structurally diverse β-hydroxy esters with good yields and enantioselectivities under mild conditions. Importantly, the broad substrate scope of this methodology enabled rapid accesses to several natural products and their analogues as exemplified by phenylpropanoid, phaitanthrin B, and phthalide.

Highly enantioselective Ir/f-amphox-catalyzed hydrogenation of ketoamides: efficient access to chiral hydroxy amides

Asymmetric synthesis of chiral hydroxy amides has been successfully accomplished by asymmetric hydrogenation of prochiral α-, β-, γ-, δ-keto amides catalyzed by Ir/f-amphox with up to >99% conversion and >99% ee.

Iridium/f-ampha-catalyzed asymmetric hydrogenation of aromatic α-keto esters

We herein report an iridium/f-ampha catalytic system for the asymmetric hydrogenation of aromatic α-keto esters.

Chiral catalysts immobilized on achiral polymers: effect of the polymer support on the performance of the catalyst

Achiral polymeric supports can have important positive effects on the activity, stability and selectivity of supported chiral catalysts.

Recent developments in functionalization of acyclic α-keto amides

This review describes the synthetic utility of α-keto amides to synthesize various important molecules via mono, dual and triple functionalization reactions.

Synthetic methodologies and spatial organization of metal chelate dendrimers and star and hyperbranched polymers

The synthetic methodologies, physico-chemical peculiarities, properties, and structure of metal chelate dendrimers and star and hyperbranched polymers are considered.

Ir-catalyzed asymmetric hydrogenation of β-keto esters with chiral ferrocenyl P,N,N-ligands

The Ir-catalyzed asymmetric hydrogenation of β-keto esters with chiral ferrocenyl P,N,N-ligands has been developed, providing the corresponding β-hydroxy esters in good to excellent enantioselectivities.

Axially Chiral Dimeric Naphthalene and Naphthoquinone Metabolites, from Root Cultures of the West African Liana Triphyophyllum peltatum

Root cultures of the West African liana Triphyophyllum peltatum were initiated from stem explants of in vitro cultivated shoots. From these organ cultures, three new binaphthalenes, one binaphthoquinone, and two (bi)naphthalene glucosides were isolated, with substitution patterns related to those of the naphthylisoquinoline alkaloids, which are the "normal" main metabolites of T. peltatum. The structures of the diglucoside dioncoquinoside A (1) and of the axially chiral biaryls triphyoquinols A1 (3), A2 (4), and B (5), triphyoquinoside A (6), and triphyoquinone A (7) were elucidated by spectroscopic analysis (HRESIMS, 1D and 2D NMR) and by application of electronic circular dichroism (ECD) spectroscopy in combination with the exciton chirality method and quantum-chemical ECD calculations. The root cultures likewise produced the known alkaloids dioncophylline A (8), 5'-O-demethyldioncophylline A (9), dioncopeltine A (10), habropetaline A (11), and 5'-O-methyldioncophylline D (12a/b), the naphthalene glucoside plumbaside A (2), and the naphthoquinones plumbagin (13), droserone (14), and 8-hydroxydroserone (15).

Synthesis of Dendrimers with a Bidentate Phosphine Core Ligand Having Carboxy Groups at the Peripheral Layer and Their Application to Aqueous Media Cross-Coupling Reactions

We prepared a series of dendrimers with a bidentate phosphine core ligand having carboxy groups at the peripheral layer. By employing the corresponding water-soluble dendritic phosphine-palladium complex as a catalyst, the aqueous media Suzuki-Miyaura reaction and Tsuji-Trost reaction proceeded to provide the corresponding cross-coupling product.

Enantioselective gold-catalyzed intermolecular [2 + 2]-cycloadditions of 3-styrylindoles with N-allenyl oxazolidinone

A series of novel chiral monophosphine ligands Xiang-Phoses were designed and have been applied to the enantioselective gold-catalyzed intermolecular [2 + 2]-cycloaddition of 3-styrylindoles 1 with N-allenyl oxazolidinone 2.

Asymmetric hydrogenation in the core of dendrimers

The transition metal complexes containing chiral phosphorus ligands are the most widely and successfully used catalysts in asymmetric hydrogenation of unsaturated compounds. However, a major problem associated with these homogeneous catalytic systems is the separation and recycling of the often expensive and easily oxidized chiral catalysts. In addition, many hydrogenation reactions still lack efficient chiral catalysts, and the stereoselectivities in many hydrogenation reactions are substrate-dependent. Therefore, the development of highly effective and recyclable chiral phosphorus catalysts is highly desirable. Over the past few decades, a number of chiral catalysts have been successfully anchored onto different supports, such as cross-linked polymeric resins and inorganic materials. However, most of the classical supported chiral catalysts suffered from inferior catalytic properties to their homogeneous counterparts due to poor accessibility, random anchoring, and disturbed geometry of the active sites in the solid matrix. To overcome this drawback, dendrimers, which have well-defined and globular macromolecular architectures serve as a promising type of soluble catalyst support. The catalytic sites are generally located at the core or on the periphery of the dendrimer, and the resulting dendritic catalysts are designable. Incorporation of a chiral catalyst into a sterically demanding dendrimer will create a specific microenvironment around the catalytic site and thus influence the catalytic performance of the metal center, like an enzyme does. In this Account, we survey the development of core-functionalized chiral dendritic phosphorus ligands for asymmetric hydrogenation mainly by our research group. Several series of chiral dendritic phosphorus ligands, including diphosphines, monodentate phosphoramidites, and P,N-ligands, have been synthesized by attaching the corresponding chiral phosphorus units into the core or the focal point of Fréchet-type dendrons. Their transition metal (Ru, Rh, or Ir) complexes have been applied in the asymmetric hydrogenation of prochiral olefins and ketones, as well as some challenging imine-type substrates. All reactions were carried out in a homogeneous manner, and the structure-property relationships in some cases were established. The sterically demanding dendritic wedges were found to play important roles in catalytic properties, and better catalytic activities or enantioselectivities or both than those obtained from the corresponding monomeric catalysts were achieved in most cases. In addition, the dendritic catalysts could be readily recycled by means of solvent precipitation, water- or temperature-induced two-phase separation. Our study has thus demonstrated that dendrimer catalysis could combine the advantages of both classical heterogeneous and homogeneous catalysis.