A Theoretically-Guided Optimization of a New Family of Modular P,S-Ligands for Iridium-Catalyzed Hydrogenation of Minimally Functionalized Olefins

The Effect of Conformational Freedom vs Restriction on the Rate in Asymmetric Hydrogenation: Iridium-Catalyzed Regio- and Enantioselective Monohydrogenation of Dienones

Transition metal-catalyzed asymmetric hydrogenation constitutes an efficient strategy for the preparation of chiral molecules. When dienes are subjected to hydrogenation, control over regioselectivity still presents a large challenge and the fully saturated alkane is often yielded. A few successful monohydrogenations of dienes have been reported, but hitherto these are only efficient for dienes comprised of two distinctly different olefins. Herein, the reactivity of a conjugated carbonyl compound as a function of their conformational freedom is studied, based on a combined experimental and theoretical approach. It was found that alkenes in the (s)-cis conformation experience a large rate acceleration while (s)-trans restrained alkenes undergo hydrogenation slowly. Ultimately, this reactivity aspect was exploited in a novel method for the monohydrogenation of dienes based on conformational restriction ((s)-cis vs (s)-trans). This mode of discrimination conceptually differs from existing monohydrogenations and dienones constructed of two olefins similar in nature could efficiently be hydrogenated to the chiral alkene (up to 99 % ee). The extent of regioselection is even powerful enough to overcome the conventional reactivity order of substituted olefins (di>tri>tetra). This high yielding and atom-economical protocol provides an interesting opportunity to instal a stereogenic center on a carbocycle, while leaving a synthetically useful alkene untouched.

Evolution of phosphorus-thioether ligands for asymmetric catalysis

In the early 1990s chiral P-thiother ligands emerged as promising ligands in the field of asymmetric catalysis, with the development of many P-thioether ligand families. However, only a few of them have shown a broad reaction and substrate scope. So, compared with other heterodonor ligands such as the widely studied P-N ligands, their impact in asymmetric catalysis was not realised until recently. This has been mainly attributed to the difficulty of controlling the configuration at the sulfur atom when coordinated to the metal. More recently, it has been found that this problem could be solved by a rigorous choice of the ligand scaffold, a process usually aided by mechanistic studies. This allowed the recent discovery of new P-thioether ligand families with a broader versatility, both in reactions and in substrate/reagent scope. This feature article aims to highlight those new P-thioether ligand libraries and the relationship between the structure and catalytic performance.

Rh-Catalyzed Asymmetric Hydrogenation of α,β- and β,β-Disubstituted Unsaturated Boronate Esters

A highly enantioselective hydrogenation of α,β-unsaturated boronate esters catalyzed by Rh-(S)-DTBM-Segphos complex has been developed. Both (Z)-α,β- and β,β-disubstituted substrates can be successfully hydrogenated to afford chiral boronates with excellent enantioselectivities, up to 98 % ee. Furthermore, the obtained chiral boronate esters, as important versatile synthetic intermediates are successfully transformed to the corresponding chiral alcohols, amines and other important derivatives with maintained enantioselectivities.

Ir–Biaryl phosphite–oxazoline catalyst libraries: a breakthrough in the asymmetric hydrogenation of challenging olefins

This work describes our progress in the successful development of phosphite/phosphinite–oxazoline ligands for the Ir-catalyzed asymmetric hydrogenation of challenging olefins.

Chemo- and Enantioselective Catalytic Hydrogenation of α,β-Unsaturated Ketones and Aldehydes as a Tool to Introduce Chiral Centers at α- or β-Positions of Ketones

Catalytic enantioselective hydrogenations of acyclic and cyclic α,β-unsaturated ketones and aldehydes are useful protocols for introduction of chiral centers at α- and/or β-positions of ketones especially in process scale reactions, which are reviewed in addition to conjugate and organocatalytic transfer reductions from the literatures since 2000.

Adaptable P-X Biaryl Phosphite/Phosphoroamidite-Containing Ligands for Asymmetric Hydrogenation and C-X Bond-Forming Reactions: Ligand Libraries with Exceptionally Wide Substrate Scope

In this personal review, we present our efforts in the design of ligand libraries for the discovery of suitable metal catalysts for asymmetric hydrogenation and C-X bond-forming reactions.

Development of Chiral Spiro P-N-S Ligands for Iridium-Catalyzed Asymmetric Hydrogenation of β-Alkyl-β-Ketoesters

The chiral tridentate spiro P-N-S ligands (SpiroSAP) were developed, and their iridium complexes were prepared. Introduction of a 1,3-dithiane moiety into the ligand resulted in a highly efficient chiral iridium catalyst for asymmetric hydrogenation of β-alkyl-β-ketoesters, producing chiral β-alkyl-β-hydroxyesters with excellent enantioselectivities (95-99.9% ee) and turnover numbers of up to 355,000.