Enantioselective merged gold/organocatalysis

Gold complexes, because of their unique carbophilic nature, have evolved as efficient catalysts for catalyzing various functionalization reactions of C-C multiple bonds. However, the realization of enantioselective transformations via gold catalysis remains challenging due to the geometrical constraints and coordination behaviors of gold complexes. In this context, merged gold/organocatalysis has emerged as one of the intriguing strategies to achieve enantioselective transformations which could not be possible by using a single catalytic system. Historically, in 2009, this field started with the merging of gold with axially chiral Brønsted acids and chiral amines to achieve enantioselective transformations. Since then, based on the unique reactivity profiles offered by each catalyst, several reports utilizing gold in conjunction with various chiral organocatalysts such as amines, Brønsted acids, N-heterocyclic carbenes, hydrogen-bonding and phosphine catalysts have been documented in the literature. This article demonstrates an up-to-date development in this field, especially focusing on the mechanistic interplay of gold catalysts with chiral organocatalysts.

2-Oxindole and related heterocycles: synthetic methodologies for their natural products and related derivatives

Natural goods, medications, and pharmaceutically active substances all contain substituted oxindoles. Generally, the C-3 stereocenter of the substituents of oxindoles and their absolute arrangement have a substantial impact on the bioactivity of these substances. In this case, the desire for contemporary probe and drug-discovery programs for the synthesis of chiral compounds using desirable scaffolds with high structural diversity further drives research in this field. Also, the new synthetic techniques are generally simple to apply for the synthesis of other similar scaffolds. Herein, we review the distinct approaches for the synthesis of diverse useful oxindole scaffolds. Specifically, the research findings on the naturally existing 2-oxindole core and a variety of synthetic compounds having a 2-oxindole core are discussed. We present an overview of the construction of oxindole-based synthetic and natural products. In addition, the chemical reactivity of 2-oxindole and its related derivatives in the presence of chiral and achiral catalysts are thoroughly discussed. The data compiled herein provides broad information related to the bioactive product design, development, and applications of 2-oxindoles and the reported techniques will be helpful for the investigation of novel reactions in the future.

Forming All-Carbon Quaternary Centers by Geminal Difunctionalization of Diazo Compounds with N,N-Disubstituted Anilines and Allylic Carbonates

A novel three-component reaction of N,N-disubstituted anilines, diazo compounds, and allylic carbonates has been developed by using a rhodium-palladium dual catalysis, providing an effective protocol for the construction of tetrasubstituted esters bearing an all-carbon quaternary center as well as an allylic moiety in one pot.

Au-Catalyzed Formal Allylation of Diazo(thio)oxindoles: Application to Tandem Asymmetric Synthesis of Quaternary Stereocenters

We report an efficient Au(I)-catalyzed formal allylation of diazo(thio)oxindoles using allyltrimethylsilane to give 3-allyl (thio)oxindoles, which are difficult to access by using traditional alkylation methods under basic conditions. The approach enables a highly stereoselective synthesis of quaternary (thio)oxindoles via a formal allylation-asymmetric Michael addition sequence. These adducts are versatile synthons for spirocyclic (thio)oxindoles. Initial biological studies reveal that chiral thiooxindoles show promising antiproliferation activity that is better than that of the corresponding oxindoles.

Catalytic Enantioselective Transfer Hydrogenation-Carboxylative Cyclization to 4-Fluoroalkyl 2-Oxazolidinone with CO2 as the C1 Synthon

We report a sequential catalytic asymmetric transfer hydrogenation-carboxylative cyclization for the facile construction of chiral 4-fluoroalkyl 2-oxazolidinones with high enantioselectivity. The resulting 2-oxazolidinones can be easily elaborated to synthetic useful chiral β-fluoroalkyl β-amino alcohols. This research also represents a rare example of catalytic asymmetric sequential reactions using CO₂ as a C1 synthon as well as carboxylative cyclization of α-fluoroalkyl propargylamines.

An uncoordinated tertiary nitrogen based tricarboxylate calcium network with Lewis acid-base dual catalytic sites for cyanosilylation of aldehydes

The design and utilization of dual sites for synergistic catalysts has been recognised as an efficient method towards high-efficiency catalysis in the cyanosilylation of aldehydes, which gives key intermediates for the synthesis of a number of valuable natural and pharmaceutical compounds. However, most of the reported dual-site catalysts for this reaction were homogeneous, accompanied by potential deactivation through internal complexation of the dual sites. Herein, by the rational selection of an uncoordinated tertiary nitrogen based tricarboxylic ligand (tris[(4-carboxyl)-phenylduryl]amine, H3TCBPA), a new three-dimensional calcium-based metal-organic framework (MOF), Ca3(TCBPA)2(DMA)2(H2O)2 (1, where TCBPA = ionized tris[(4-carboxyl)-phenylduryl]amine and DMA = N,N-dimethylacetamide), possessing accessible dual catalytic sites, Lewis-basic N and Lewis-acidic Ca, has been designed and constructed by a one-pot solvothermal reaction. As expected, 1 is capable of dually and heterogeneously catalysing the cyanosilylation of aldehydes at room temperature, and can be reused for at least 6 runs with a maximum turnover number (TON) of 1301, which is superior to most reported cases. Additionally, 1 shows CO2 adsorption ability and conversion with epoxides, which is beneficial for the establishment of a sustainable society.

Gold Catalysis and Furans: A Powerful Match for Synthetic Connections

This review summarizes the advances made on the synthesis and functionalization of furans via gold catalysis during the period between 2016 and 2020. A separate section is dedicated to the tandem gold-catalyzed synthesis and functionalization of furans.

1 Introduction

2 Gold-Catalyzed Synthesis of Furans

2.1 Cycloisomerizations of Alkynyl and Cumulenyl Alcohols

2.2 Cycloisomerizations of Alkynyl and Allenyl Ketones

2.3 Reactions with External Oxidants

2.4 Miscellaneous

3 Gold-Catalyzed Functionalization of Furans

3.1 Cycloadditions

3.2 Furan Ring Decorations

3.3 Reactions Involving Furan Ring Opening

4 Gold-Catalyzed Tandem Synthesis and Functionalization of Furans­

4.1 Cycloisomerizations Followed by Gold-Catalyzed Cycloaddition

4.2 Cycloisomerizations to a Gold 1,3- or 1,4-Dipole and Intermolecular Annulation

4.3 Cycloisomerizations to a Gold Carbene and Intermolecular Trapping

5 Conclusion

Hydrosilane-Assisted Synthesis of Urea Derivatives from CO2 and Amines

A methodology employing CO₂, amines, and phenylsilane was discussed to access aryl- or alkyl-substituted urea derivatives. This procedure was characterized by adopting hydrosilane to promote the formation of ureas directly, without the need to prepare silylamines in advance. Control reactions suggested that FeCl₃ was a favorable additive for the generation of ureas, and this 1,5,7-triazabicyclo[4.4.0]dec-5-ene-catalyzed reaction might proceed through nucleophilic addition, silicon migration, and the subsequent formal substitution of silylcarbamate.

Synthesis of fused-tetrahydropyrimidines: one-pot methylenation–cyclization utilizing two molecules of CO2

A methylenation–cyclization reaction employing cyclic enaminones with primary aromatic amines and two molecules of CO₂ to furnish fused-tetrahydropyrimidines has been developed.

Catalytic selective mono- and difluoroalkylation using fluorinated silyl enol ethers

This feature article highlights our recent achievements in catalytic selective mono- and difluoroalkylation using fluorinated silyl enol ethers (FSEEs).

Development of Synthetic Methodologies via Catalytic Enantioselective Synthesis of 3,3-Disubstituted Oxindoles

3,3-Disubstituted oxindoles are widely distributed in natural products, drugs, and pharmaceutically active compounds. The absolute configuration and the substituents on the fully substituted C3 stereocenter of the oxindole often significantly influence the biological activity. Therefore, tremendous efforts have made to develop catalytic enantioselective syntheses of this prominent structural motif. Research in this area is further fueled by the ever-increasing demand for modern probe- and drug-discovery programs for synthetic libraries of chiral compounds that are derived from privileged scaffolds with high structural diversity. Notably, the efficient construction of fully substituted C3 stereocenters of oxindole, tetrasubstituted or all-carbon quaternary, spirocyclic or not, also becomes a test ground for new synthetic methodologies. We have been engaged in developing efficient methods for diversity-oriented synthesis of chiral 3,3-disubstituted oxindoles from readily available starting materials. We have systematically developed catalytic enantioselective methods to prepare 3-substituted 3-hydroxyoxindoles, 3-aminooxindoles, and 3-thiooxindoles, quaternary oxindoles, and spirocyclic oxindoles. These protocols can be classified into six approaches: (1) enantioselective addition of nucleophiles to isatins or isatin ketimines; (2) unprotected 3-substituted oxindoles as nucleophiles; (3) functionalization of oxindole-derived tetrasubstituted alkenes; (4) desymmetrization of oxindole-based diynes; (5) spirocyclopropyl oxindoles as donor-acceptor (D-A) cyclopropanes; and (6) elaboration of diazooxindoles. By the use of these methods, chiral oxindoles with rich structural diversity are readily accessed with high to excellent enantioselectivity. Some methods have been used for the enantioselective formal or total synthesis of natural products, bioactive compounds, or their analogues. On the basis of these studies, we developed synthetic methodologies that have potential application. We designed phosphoramide-based bifunctional catalysts for the efficient construction of quaternary oxindoles: a cinchona-alkaloid-derived phosphoramide for the Michael addition of unprotected 3-substituted oxindoles to nitroolefins with broad substrate scope and a chiral 1,2-cyclohexanediamine-derived bifunctional phosphoramide for the activation of fluorinated enol silyl ethers for the addition to isatylidene malononitrile. The phosphoramide-based catalysts achieved better enantiofacial control than the analogous H-bond-donor-derived catalysts in these reactions, suggesting the potential of the former in new chiral catalyst development. We identified chiral Au(I) and Hg(II) catalysts for olefin cyclopropanation of diazooxindoles. We further disclosed the effective activation of spirocyclopropyl oxindoles by using electron-withdrawing N-protecting groups for enantioselective [3 + 3] cycloaddition, offering the promise of constructing a diverse range of spirocyclic oxindoles by the use of such monoactivated D-A cyclopropanes. We developed tandem sequences that allow the facile synthesis of 3,3-disubstituted oxindoles from simple starting materials in a one-pot operation, including a tandem Morita-Baylis-Hillman/bromination/[3 + 2] annulation sequence, a hydrogenation/ketimine formation/asymmetric 6π electrocyclization sequence, a C-H functionalization/Michael addition or amination sequence, and an aza-Wittig/Strecker sequence. We designed oxindole-based diynes to realize a highly enantioselective Cu-catalyzed alkyne-azide cycloaddition (CuAAC), outlining the desymmetrization of prochiral diynes as an effective strategy to exploit asymmetric CuAAC. This Account focuses on the synthetic methodologies developed in our group for the catalytic enantioselective synthesis of 3,3-disubstituted oxindoles and provides an overview of our research on the design, development, and applications of these methods that will provide useful insights for the exploration of new reactions.

Two metal–organic frameworks based on pyridyl–tricarboxylate ligands as size-selective catalysts for solvent-free cyanosilylation reaction

Two novel 3D metal–organic frameworks based on multifunctional pyridyl–tricarboxylate ligands as size-selective heterogeneous catalysts for the cyanosilylation of acetaldehydes.

Stereoselective Synthesis of 3-(1,3-Diarylallylidene)oxindoles via a Palladium-Catalyzed Tandem Reaction

We have developed an efficient three-component tandem reaction for the synthesis of 3-(1,3-diarylallylidene)oxindoles combining three palladium-catalyzed reactions: the Sonogashira, Heck, and Suzuki-Miyaura reactions. This method allows a stereoselective approach to each (E)- and (Z)-isomer by ligand change and controlling the reaction temperature.

Highly Stereoselective Gold-Catalyzed Coupling of Diazo Reagents and Fluorinated Enol Silyl Ethers to Tetrasubstituted Alkenes

We report a highly stereoselective synthesis of all-carbon or fluorinated tetrasubstituted alkenes from diazo reagents and fluorinated enol silyl ethers, using C-F bond as a synthetic handle. Cationic Au^I catalysis plays a key role in this reaction. Remarkable fluorine effects on the reactivity and selectivity was also observed.

Triple zirconocene/brønsted acid/CuO cooperative and relay catalysis system for tandem Mannich addition/C–C formative cyclization/oxidation

Triple zirconocene/brønsted acid/CuO cooperative and relay catalysis system for tandem Mannich addition/C–C formative cyclization/oxidation.

Gold/silver-catalyzed controllable regioselective vinylcarbene insertion into O–H bonds

The controllable regioselective vinylcarbene insertion into O–H bonds of 2-pyridones/benzyl alcohols has been realized.

Gold-catalyzed highly regio- and enantioselective vinylcarbene insertion into O–H bonds of 2-pyridones

The first gold-catalyzed enantioselective carbene insertion into O–H bonds has been achieved.

Diastereo- and enantioselective construction of cyclohexanone-fused spirospyrazolones containing four consecutive stereocenters through asymmetric sequential reactions

The diastereo- and enantioselective synthesis of cyclohexanone-fused spirospyrazolones through an asymmetric Michael/Michael/aldol cascade reaction catalyzed by squaramide and diphenylprolinol silyl ether, followed by a sequential oxidation was developed.