Organosilanes in Metal-Catalyzed, Enantioselective Reductions

Rhodium-catalyzed synthesis of Si-stereogenic alkoxysilanes and silyl enol ethers via hydrosilylation of carbonyl compounds

A highly efficient rhodium-catalyzed asymmetric hydrosilylation of aldehydes, ketones, and α,β-unsaturated ketones with dihydrosilanes is developed, that allows the rapid assembly of a variety of Si-stereogenic alkoxysilanes and silyl enol ethers in good yields and enantioselectivities under mild conditions. The applicability of this methodology was demonstrated by a series of stereospecific transformations to construct diverse Si-stereogenic derivatives.

The role of silicon in drug discovery: a review

This review aims to highlight the role of silicon in drug discovery. Silicon and carbon are often regarded as being similar with silicon located directly beneath carbon in the same group in the periodic table. That being noted, in many instances a clear dichotomy also exists between silicon and carbon, and these differences often lead to vastly different physiochemical and biological properties. As a result, the utility of silicon in drug discovery has attracted significant attention and has grown rapidly over the past decade. This review showcases some recent advances in synthetic organosilicon chemistry and examples of the ways in which silicon has been employed in the drug-discovery field.

One-pot transfer hydrogenation and reductive amination of polyenals

The efficient preparation of long-chain amines via a one-step transfer-hydrogenation/reductive-amination reaction (THRA) of polyenals has been achieved. This strategy, which combines transfer hydrogenation and reductive amination, significantly enhances the synthetic efficiency of amino compounds. Additionally, this protocol offers a practical method for carbon-chain elongation/amination to construct long-chain amino compounds. The reaction system exhibits remarkable versatility in substrate scope using a non-noble ruthenium catalyst with formate and isopropanol as hydrogen sources, making it an appealing method for drug synthesis and molecular modification.

Axial Ligand Enables Synthesis of Allenylsilane through Dirhodium(II) Catalysis

Described herein is a dirhodium(II)-catalyzed silylation of propargyl esters with hydrosilanes, using tertiary amines as axial ligands. By adopting this strategy, a range of versatile and useful allenylsilanes can be achieved with good yields. This reaction not only represents a SN2'-type silylation of the propargyl derivatives bearing a terminal alkyne moiety to synthesize allenylsilanes from simple hydrosilanes, but also represents a new application of dirhodium(II) complexes in catalytic transformation of carbon-carbon triple bond. The highly functionalized allenylsilanes that are produced can be transformed into a series of synthetically useful organic molecules. In this reaction, an intriguing ON-OFF effect of the amine ligand was observed. The reaction almost did not occur (OFF) without addition of Lewis base amine ligand. However, the reaction took place smoothly (ON) after addition of only catalytic amount of amine ligand. Detailed mechanistic studies and density functional theory (DFT) calculations indicate that the reactivity can be delicately improved by the use of tertiary amine. The fine-tuning effect of the tertiary amine is crucial in the formation of the Rh-Si species via a concerted metalation deprotonation (CMD) mechanism and facilitating β-oxygen elimination.

Nickel-Catalyzed Double Deoxygenative C-N Coupling of Acyloxyamines

A double deoxygenative C-N coupling protocol has been developed by employing acyloxyamines through N-O bond activation. The C-N bond formation under mild reaction conditions, employing NiCl2 as the catalyst and cataCXiumA as a ligand, results in the production of a diverse array of alkylated secondary or tertiary amines, including heterocyclic amines. This method introduces a novel catalytic strategy that emphasizes the versatility of nickel-catalyzed reactions, extending beyond traditional synthetic boundaries.

Enantioselective Transformations in the Synthesis of Therapeutic Agents

The proportion of approved chiral drugs and drug candidates under medical studies has surged dramatically over the past two decades. As a consequence, the efficient synthesis of enantiopure pharmaceuticals or their synthetic intermediates poses a profound challenge to medicinal and process chemists. The significant advancement in asymmetric catalysis has provided an effective and reliable solution to this challenge. The successful application of transition metal catalysis, organocatalysis, and biocatalysis to the medicinal and pharmaceutical industries has promoted drug discovery by efficient and precise preparation of enantio-enriched therapeutic agents, and facilitated the industrial production of active pharmaceutical ingredient in an economic and environmentally friendly fashion. The present review summarizes the most recent applications (2008-2022) of asymmetric catalysis in the pharmaceutical industry ranging from process scales to pilot and industrial levels. It also showcases the latest achievements and trends in the asymmetric synthesis of therapeutic agents with state of the art technologies of asymmetric catalysis.

Synthesis and catalytic performance of nickel phosphinite pincer complexes in deoxygenative hydroboration of amides

A series of imino-POCN^R, amino-POCN^R2, and bis(phosphinite) POCOP pincer complexes of Ni(II) were prepared and tested in catalytic deoxygenative hydroboration of amides with HBPin to the corresponding amines. In contrast to the deoxygenative hydrosilylation approach, primarily developed for tertiary amides, superior reactivity in Ni-catalyzed deoxygenative hydroboration was demonstrated for secondary carboxamides. The bis(phosphinite) hydride complex (POCOP)NiH proved the most active in these reactions, tolerating potentially reducible functionalities such as internal alkenes, esters, nitriles, heteroaromatic compounds, and tertiary amides. Preferable hydroboration of secondary amides was also demonstrated in the presence of primary amide functionalities. The reactions were conducted at 60-80 °C, representing a rare example of a base-metal catalytic system for selective deoxygenation of secondary amides to the corresponding amines under mild conditions. In contrast to secondary amides, deoxygenative hydroboration of primary amides was demonstrated using an iminophosphinite pre-catalyst (POCN^Dmp)Ni(CH₂TMS) (Dmp = 2,6-Me₂C₆H₃). Deoxygenation reactions were suggested to proceed via a direct C-O bond cleavage mechanism, which is triggered by dehydrogenative N-borylation to access more electrophilic N-borylamides amenable to the addition of HBPin to the carbonyl group.

Catalytic Asymmetric Conjugate Reduction

Enantioselective reduction reactions are privileged transformations for the construction of trisubstituted stereogenic centers. While these include established synthetic strategies, such as asymmetric hydrogenation, methods based on the enantioselective addition of hydridic reagents to electrophilic prochiral substrates have also gained importance. In this context, the asymmetric conjugate reduction (ACR) of α,β-unsaturated compounds has become a convenient approach for the synthesis of chiral compounds with trisubstituted stereocenters in α-, β-, or γ-position to electron-withdrawing functional groups. Because such activating groups are diverse and amenable of further derivatizations, ACRs provide a general and powerful synthetic entry towards a variety of valuable chiral building blocks. This Review provides a comprehensive collection of catalytic ACR methods involving transition-metal, organic, and enzymatic catalysis since its first versions dating back to the late 1970s.

Fe-catalyzed denitrative cyanoalkylation of nitroalkenes with cycloketone oxime esters via reductive C–C bond formation

An iron catalyzed reductive denitrative cyanoalkylation of nitroalkenes with cycloketone oxime esters using Zn as the reductant has been successfully established in which the NO2 of nitroalkenes eventually acts as a leaving group.

Layered Double Hydroxides as Reusable Catalysts for Cyclocondensation of Amidines and Aminoalcohols: Access to Multi-functionalized Oxazolines

An efficient catalytic protocol based on reusable MgAl-layered double hydroxides has been developed for the synthesis of multi-functionalized oxazolines via the cyclocondensation of amidines and aminoalcohols. The developed method has a broad substrate scope and excellent functional group tolerance and uses a reusable catalyst. The catalyst can be conveniently recycled by filtration and reused for at least five times without obvious deactivation. Additionally, the selective ortho C-H silylation of oxazolines was performed using Ru(II) as the catalyst and triethyl silane as the silylating reagent, which proved to be a convenient and practical method for the synthesis of versatile organosilyl-functionalized oxazolines with advantageous biological and physical properties.