Probing the Effects of Heterocyclic Functionality in [(Benzene)Ru(TsDPENR)Cl] Catalysts for Asymmetric Transfer Hydrogenation

Manganese(I)-Catalyzed Enantioselective Formal Anti-Markovnikov Hydroalkoxylation of Racemic Allylic Alcohols: A Borrowing Hydrogen Access

An enantioselective manganese(I)-catalyzed formal anti-Markovnikov hydroalkoxylation of racemic allylic alcohols has been developed using a chiral N6-type macrocyclic ligand, affording a wide range of chiral γ-alkoxypropyl alcohols in high isolated yields with excellent enantioselectivities. The synthetic utility of this protocol was further proven by gram-scale synthesis of chiral γ-alkoxypropanol 3n and derivatization of chiral γ-alkoxypropanol 3a to a drug molecule, (S)-dapoxetine, for the treatment of premature ejaculation and erectile dysfunction. Mechanistic studies support that the reaction proceeds via a hydrogen-borrowing cascade reaction pathway.

The Ir-Catalyzed Asymmetric Hydrogenation of α-Halogenated Ketones Utilizing Cinchona-Alkaloid-Derived NNP Ligand to Produce (R)- and (S)-Halohydrins

The asymmetric hydrogenation of α-halogenated ketones with iridium catalyst was developed, utilizing easily accessed cinchona-alkaloid-based NNP ligands. Various α-chloroacetophenones, heterocyclic thienyl and furanyl substrates, and even bromoketones were completely converted to the desired chiral halohydrins by this protocol. Both (R)- and (S)-chiral halohydrins can be prepared by changing the configurations of the chiral ligand NNP with up to 99.6% ee (enantiomeric excess) and 98.8% ee, respectively. Also, a gram-scale experiment was carried out efficiently.

TiCl4-Catalyzed Hydroboration of Ketones with Ammonia Borane

Investigation of a variety of Lewis acids for the hydroboration-hydrolysis (reduction) of ketones with amine-boranes has revealed that catalytic (10 mol %) titanium tetrachloride (TiCl₄) in diethyl ether at room temperature immensely accelerates the reaction of ammonia borane. The product alcohols are produced in good to excellent yields within 30 min, even with ketones which typically requires 24 h or longer to reduce under uncatalyzed conditions. Several potentially reactive functionalities are tolerated, and substituted cycloalkanones are reduced diastereoselectively to the thermodynamic product. A deuterium labeling study and ¹¹B NMR analysis of the reaction have been performed to verify the proposed hydroboration mechanism.

Heterocycle-containing Noyori-Ikariya catalysts for asymmetric transfer hydrogenation of ketones

The synthesis of a range of N-(heterocyclesulfonyl)-functionalised Noyori-Ikariya catalysts is described. The complexes were prepared through a short sequence from C2-symmetric 1,2-diphenylethylene-1,2-diamine (DPEN) and were characterised by a range of methods including X-ray crystallography. The complexes were active catalysts for the asymmetric transfer hydrogenation (ATH) of a range of acetophenone derivatives, giving products of high ee in most cases, with notably good results for ortho-substituted acetophenones.

Rh(iii)-Catalyzed diastereoselective transfer hydrogenation: an efficient entry to key intermediates of HIV protease inhibitors

A highly efficient diastereoselective transfer hydrogenation of α-aminoalkyl α′-chloromethyl ketones catalyzed by a tethered rhodium complex was developed and successfully utilized in the synthesis of the key intermediates of HIV protease inhibitors.