Gold-Catalysed Intramolecular Reaction of Alkynes with Sulfoximines Acting as N- and O-Transfer Reagents

Among the nucleophilic oxidants employed in the gold-catalysed oxidation of alkynes, sulphur-based reagents have played a substantial role since the beginning, granting access to the respective gold carbene intermediates. Herein, we describe the first example of the substance class of sulfoximines being used as atom transfer reagents to alkynes in gold catalysis. Based on the transformation of N-(2-alkynylphenyl) sulfoximines to 3H-indol-3-ones, it is demonstrated that the sulfoximine functionality is capable of selectively transferring first its nitrogen moiety to the alkyne, forming the α-imino gold carbene, which is then oxidised by the released sulfoxide moiety in a second step via a pseudo-intramolecular mechanism-a distinctive feature that differentiates this work mechanistically from earlier studies. A combination of extensive experimental and theoretical studies provides evidence for this mechanistic rationale. As no external reagents for the 1,2-difunctionalisation of the alkyne unit are required, a wide variety of functional groups are tolerated in the transformation, affording the desired 3H-indol-3-ones in mostly good yields. It was further also showcased that it is possible to combine our methodology with additional transformations of the 3H-indol-3-one core in one-pot procedures, allowing facile access to C2-quaternary indolin-3-one structures.

One-Pot Synthesis of N-Fused Quinolone-4 Tetracyclic Scaffolds from 2,2-Disubstituted Indolin-3-ones

A cascade transformation of C2-quaternary indoxyls leading to an efficient assembly of complex (dihydro)indolo[1,2-a]quinolin-5-one ring systems is reported. The method involves the gram-scale preparation of 2-(2-aryl-3-oxoindolin-2-yl)-2-phenylacetonitriles which are then converted with methyl ketones to the corresponding 2-(2-oxo-2-aryl(alkyl)ethyl)-2-phenylindolin-3-ones. The latter can either be isolated with good yields (75-96%) or, in the case of o-nitroacetophenone, used in situ for further base-assisted intramolecular SNAr cyclization resulting in indoxyl-fused quinolone-4 hybrids (up to 95%).

Enantioselective de novo construction of 3‑oxindoles via organocatalyzed formal [3 + 2] annulation from simple arylamines

The de novo construction of enantioenriched 3-hydroxyindolenines and 3-oxindoles from easily available starting materials has been highly desired. Herein, an enantioselectively intermolecular direct [3 + 2] annulation of aryl amine with 2,3-diketoesters to construct 3-hydroxyindolenines with a chiral tertiary alcohol has been disclosed. The results of control experiments and DFT calculation revealed that π - π interaction plays a pivotal role in the enantioselectivity-determining process of [3 + 2] annulation. The following unusual concerted [1,2]-ester migration provides a family of chiral 3-oxindoles in good to excellent yields with excellent enantioselectivity.

Gold/Chiral Amine Relay Catalysis Enables Asymmetric Synthesis of C2-Quaternary Indolin-3-ones

A mild and effective strategy for the asymmetric synthesis of C2-quaternary indolin-3-ones from 2-alkynyl arylazides and ketones by gold/chiral amine relay catalysis is described. In this reaction, 2-alkynyl arylazides undergo gold-catalyzed cyclization, nucleophilic attack, and oxidation to form intermediate 2-phenyl-3H-indol-3-ones, followed by an l-proline-catalyzed asymmetric Mannich reaction with ketones, to afford corresponding products in satisfactory yields with excellent enantio- and diastereoselectivities.

Pd-Catalyzed Asymmetric Allylation Reaction of 2-Aryl-3H-indol-3-ones with Allyltrimethylsilane

An efficient method for the first ene-reaction of 2-aryl-3H-indol-3-ones with allyltrimethylsilane has been developed for the first time. The reaction proceeded under the catalysis of Pd(OAc)2 and chiral phosphoric ligand L11 in the presence of Cu(CF3COO)2·XH2O, PivOH, and 5 Å molecular sieves in DMSO at 60 °C. The present methodology can avoid the impact of amine products generated by the reaction on the catalyst, and at the same time, the high catalytic activity of classical palladium catalysts still has catalytic ability for low electrophilic keto-imines. The desired products were furnished in excellent yields with good enantioselectivity.

Enantioselective Alkynylation of 2-Aryl-3H-indol-3-ones via Cooperative Catalysis of Copper/Chiral Phosphoric Acid

A facile enantioselective alkynylation of cyclic ketimines attached to a neutral functional group utilizing the dual Cu(I)-CPA catalysis is described. The strategy of the alkynylation of 2-aryl-3H-indol-3-one directly to chiral propargylic amines containing indolin-3-one moiety in good yields and enantioselectivities. Moreover, gram-scale synthesis of chiral propargylamines based C2-quaternary indolin-3-ones was performed. The synthetic applications were confirmed by transformations of the products with no decrease in the yield and enantioselectivity.

B(C6F5)3-catalyzed β-C(sp3)-H alkylation of tertiary amines with 2-aryl-3H-indol-3-ones

The β-C-H functionalization of amines is one of the most powerful tools for the synthesis of saturated nitrogen-containing heterocycles in organic synthesis. However, the β-C-H functionalization of amines via redox-neutral addition with cyclic-ketimines is still unprecedented. Herein, the β-C-H functionalization of tertiary amines is described, providing the corresponding 1,3-diamines containing the indolin-3-one moiety in high yields via the B(C₆F₅)₃-catalyzed borrowing hydrogen strategy. According to the experimental results, a possible catalytic cycle has been proposed to rationalize the process of this reaction. Notably, the β-C-H alkylation of amines is external oxidant- and transition-metal-free, which makes a significant contribution to promoting economical chemical synthesis.

Organocatalyzed Enantioselective Aza-Morita-Baylis-Hillman Reaction of Cyclic Ketimine with α,β-Unsaturated γ-Butyrolactam

The enantioselective aza-MBH reaction is an efficient strategy for constructing novel carbon-carbon bonds, providing access to multitudinous chiral densely functionalized MBH products. However, the enantioselective aza-MBH reaction of cyclic-ketimines that would generate a versatile synthon is still missing and challenging. Herein, we developed a challenging direct organocatalytic asymmetric aza-MBH reaction involving cyclic ketimines attached to a neutral functional group. Moreover, the α,β-unsaturated γ-butyrolactam was utilized as a rare nucleophile alkene in this work. The reactions provide enantiomerically enriched 2-alkenyl-2-phenyl-1,2-dihydro-3H-indol-3-ones, bearing with a tetra-substituted stereogenic center. Moreover, this reaction features high α-selectivities, high enantioselectivities (up to 99% ee), and good yields (up to 80%).

PPh3-Mediated Cascade Reaction of 2-Alkynylnitrobenzenes and Thioureas for the Construction of Imidazo[4,5-b]indole-2-thiones

A simple method for the preparation of imidazo[4,5-b]indole-2-thiones from 2-alkynylnitrobenzenes and thioureas is described. In the reaction, a Wittig-like process was triggered by PPh₃ and followed by a cyclization step. The products were afforded in yields of 70-98% under mild conditions. Additionally, the 2-alkynylnitrobenzenes were stable and could be prepared via a simple coupling step.

Chiral phosphoric acid-catalyzed enantioselective aza-Friedel-Crafts reaction of naphthols and electron-rich phenols with 2-aryl-3H-indol-3-ones

The enantioselective aza-Friedel-Crafts reaction is one of the most straightforward and efficient strategies for constructing a new carbon-carbon bond bearing quaternary stereocenter in organic synthesis, but the catalytic asymmetric aza-Friedel-Crafts reaction of naphthols/phenols with cyclic-ketimines attached to a neutral functional group remains still relatively unexplored. Herein, a highly enantioselective aza-Friedel-Crafts reaction of cyclic-ketimines and naphthols/phenols has been realized using a chiral phosphoric acid catalyst. A variety of chiral aminonaphthols (chiral indolin-3-ones) containing a quaternary stereocenter at the C2 position were obtained with excellent outcomes (up to 97% yield, 98% ee). Moreover, the synthetic utility of the enantiomerically enriched chiral aminonaphthols was demonstrated in some efficient transformations. According to the experimental results, a possible transition state model has been proposed to rationalize the origin of asymmetric induction.

Diastereoselective Access to Triazolo[1,2-a]indolines via a Bio-Inspired Oxidative Cyclization of NH-Indoles

Establishing three-dimensional chemicals by using the C₂-C₃ π bond of indoles has always been a research hotspot in organic synthesis; however, employing the oxidative C₂-C₃ π bond of indoles to generate imine which would lead to the N₁-C₂ π bond cyclization under metal-free conditions is still rare. Here, we report a bio-inspired synthesis of triazolo[1,2-a]indolines by the oxidative cyclization between NH-indoles and azomethine imines with 3,3-dimethyldioxirane as the sole oxidant under metal-free and mild conditions. This finding represents an elegant instance of tri-functionalization of NH-indoles, which provides rapid access to a broad range of triazolo[1,2-a]indolines with tetrahydroisoquinolines in one single step. Up to 86% yield and above 20:1 dr value are observed. The radical mechanism and proton migration process have been speculated.

Gold-catalyzed redox cycloisomerization/nucleophilic addition/reduction: direct access to 2-phosphoryl indolin-3-ones

An efficient gold(I)-catalyzed redox cycloisomerization/nucleophilic addition/reduction reaction of o-nitroalkynes with various H-phosphorus oxides is established. Through the intramolecular redox cyclization of o-nitroalkynes and subsequent intermolecular nucleophilic addition/reduction with no external reactant, a variety of arylphosphoryl and alkylphosphoryl indolin-3-ones with high functional-group compatibility are obtained in moderate to good yields. Mechanistic studies suggest that phosphorus nucleophiles mediate the cleavage of the N-O bond as a reductant.

Indoles Oxidative Ring-Opening/Cyclization Cascade with the 1,2-Diaminoarenes: Direct Synthesis of 2-Aryl-3-(2-aminoaryl)quinoxalines

A mild oxidative sequential tandem reaction was developed to rapidly generate 2-aryl-3-(2-aminoaryl) quinoxalines. This method exploited 2-substituted indoles as substrate to form quinoxalines in a one-pot reaction. The key to this tandem reaction was the formation of 3-iodoindoles, which underwent Kornblum-type oxidation with DMSO to generate active imine 2-substitued 3H-indol-3-ones. The active imines were captured in situ by 1,2-diaminobenzenes to construct diverse quinoxalines. The transformation can be accomplished at room temperature with excellent functional group tolerance.

A solid-supported organocatalyst for asymmetric Mannich reaction to construct C2-quaternary indolin-3-ones

A simple and novel solid-supported organocatalyst from a 2-chlorotrityl chloride resin-immobilized 4-hydroxyproline was developed, and this organocatalyst has been used for the asymmetric Mannich reaction of 2-aryl-3H-indol-3-ones and aldehydes/ketones. A series of C2-quaternary indolin-3-ones were prepared in good yields (up to 83%) and with excellent diastereoselectivities (up to 20 : 1) and enantioselectivities (up to 99% ee). In addition, the organocatalyst can be recovered by simple filtration and also be reused for the asymmetric Mannich reaction without significant loss of catalytic efficiency.

A simple and novel solid-supported organocatalyst from a 2-chlorotrityl chloride resin-immobilized 4-hydroxyproline was developed, which has been used for the asymmetric Mannich reaction of 2-aryl-3H-indol-3-ones and aldehydes/ketones.

An overview of the applications of chiral phosphoric acid organocatalysts in enantioselective additions to CO and CN bonds

Since 2004, chiral phosphoric acids (CPAs) have emerged as highyl efficient organocatalysts, providing excellent results in a wide reaction scope. In this review, the applications of CPA for enantioselective additions to CO and CN bonds are covered.

Dieckmann Condensation of Ugi N-Acylamino Amide Product: Facile Access to Functionalized 2,2-Disubstituted Indolin-3-ones

Structurally unique 2,2-disubstituted indolin-3-ones with a quaternary carbon center have been constructed through a novel C-C bond formation at the C3 position of Ugi N-acylamino amide adducts employing an organic base-mediated Dieckmann condensation. This facile, flexible protocol can be fine-tuned to construct drug-like pyrazino[1,2-a]indole fragments with the same quaternary carbon center only through the variation of the acid part in Ugi input. This novel and expeditious methodology has a broad scope and can rapidly generate the drug-like indolin-3-one core.

Regioselective Cross-Coupling of Isatogens with Boronic Acids to Construct 2,2-Disubstituted Indolin-3-one Derivatives

Herein we present a transition-metal-free cross-coupling reaction of isatogens with boronic acids through a 1,4-metalate shift of a boron "ate" complex. This coupling reaction provides a feasible method to deliver valuable 2,2-disubstituted indolin-3-one derivatives with excellent regioselectivity, which exhibit operational simplicity, good functional group tolerance, and a broad substrate scope.

Acid-catalyzed cleavage of C-C bonds enables atropaldehyde acetals as masked C2 electrophiles for organic synthesis

Acid-catalyzed tandem reactions of atropaldehyde acetals were established for the synthesis of three important molecules, 2,2-disubstituted indolin-3-ones, naphthofurans and stilbenes. The synthesis was realized using novel reaction cascades, which involved the same two initial steps: (i) S_N2' substitution, in which the atropaldehyde acted as an electrophile; and (ii) oxidative cleavage of the carbon-carbon bond of the generated phenylacetaldehyde-type products. Compared with literature methods, the present protocol not only avoided the use of expensive noble metal catalysts, but also enabled a simple operation.

Recent Advances in Selected Asymmetric Reactions Promoted by Chiral Catalysts: Cyclopropanations, Friedel–Crafts, Mannich, Michael and Other Zinc-Mediated Processes—An Update

The main purpose of this review article is to present selected asymmetric synthesis reactions in which chemical and stereochemical outcomes are dependent on the use of an appropriate chiral catalyst. Optically pure or enantiomerically enriched products of such transformations may find further applications in various fields. Among an extremely wide variety of asymmetric reactions catalyzed by chiral systems, we are interested in: asymmetric cyclopropanation, Friedel–Crafts reaction, Mannich and Michael reaction, and other stereoselective processes conducted in the presence of zinc ions. This paper describes the achievements of the above-mentioned asymmetric transformations in the last three years. The choice of reactions is related to the research that has been carried out in our laboratory for many years.

Photomediated ring contraction of saturated heterocycles

Saturated heterocycles are found in numerous therapeutics and bioactive natural products and are abundant in many medicinal and agrochemical compound libraries. To access new chemical space and function, many methods for functionalization on the periphery of these structures have been developed. Comparatively fewer methods are known for restructuring their core framework. Herein, we describe a visible light-mediated ring contraction of α-acylated saturated heterocycles. This unconventional transformation is orthogonal to traditional ring contractions, challenging the paradigm for diversification of heterocycles including piperidine, morpholine, thiane, tetrahydropyran, and tetrahydroisoquinoline derivatives. The success of this Norrish type II variant rests on reactivity differences between photoreactive ketone groups in specific chemical environments. This strategy was applied to late-stage remodeling of pharmaceutical derivatives, peptides, and sugars.

Palladium-Catalyzed One-Pot Synthesis of Pyrroloindolines from 2-Alkynyl Arylazides and Thioacetamides

A novel and efficient synthetic method for the preparation of various pyrroloindolines from 2-alkynyl arylazides and thioacetamides was developed. The reaction was carried out in a one-pot process under mild reaction conditions to afford the products in moderate to good yields, which has the potential to be used in organic synthesis.

Organocatalytic asymmetric synthesis of arylindolyl indolin-3-ones with both axial and central chirality

An efficient method for chiral phosphoric acid-catalyzed asymmetric synthesis of arylindolyl indolin-3-ones with both axial and central chirality has been developed via the reaction of 3-arylindoles with 2-aryl-3H-indol-3-ones, and the target products were obtained in high yields with excellent enantioselectivity and diastereoselectivity.

Regiodivergent Synthesis of Penta-Substituted Pyrroles through a Cascade [3 + 2] Cyclization of C-Acylimines with Activated Alkynes and Aromatic Nucleophiles

Highly robust one-pot, four-component cascade cyclization reaction of α-keto aldehydes, anilines, activated alkynes, and aromatic nucleophiles is developed to synthesize a diverse range of pharmaceutically important penta-substituted pyrroles. The reaction proceeds through the cascade cyclization of acylimines (in situ formed) with activated alkynes and aromatic nucleophiles such as indoles, pyrroles, and naphthols at room temperature under calcium(II) catalysis with high yields and broad substrate diversity.

Palladium-catalyzed α-arylation of indolin-3-ones

A method for the catalytic α-arylation of indolin-3-ones was developed. The catalytic system comprising Pd(dba)₂ and PAd₃ was found to be optimal for the transformation. The protocol features broad functional group compatibility in that a range of arylated indoxyl derivatives bearing a fully substituted carbon center was synthesized with high efficiency. A preliminary bioassay study revealed that the selected indole-substituted indolin-3-ones exhibit favorable cytotoxic activities against HCT-116 cancer cell line.

B(C6 F5 )3 /Chiral Phosphoric Acid Catalyzed Ketimine-Ene Reaction of 2-Aryl-3H-indol-3-ones and α-Methylstyrenes

The enantioselective ketimine-ene reaction is one of the most challenging stereocontrolled reaction types in organic synthesis. In this work, catalytic enantioselective ketimine-ene reactions of 2-aryl-3H-indol-3-ones with α-methylstyrenes were achieved by utilizing a B(C₆ F₅ )₃ /chiral phosphoric acid (CPA) catalyst. These ketimine-ene reactions proceed well with low catalyst loading (B(C₆ F₅ )₃ /CPA=2 mol %/2 mol %) under mild conditions, providing rapid and facile access to a series of functionalized 2-allyl-indolin-3-ones with very good reactivity (up to 99 % yield) and excellent enantioselectivity (up to 99 % ee). Theoretical calculations reveal that enhancement of the acidity of the chiral phosphoric acid by B(C₆ F₅ )₃ significantly reduces the activation free energy barrier. Furthermore, collective favorable hydrogen-bonding interactions, especially the enhanced N-H⋅⋅⋅O hydrogen-bonding interaction, differentiates the free energy of the transition states of CPA and B(C₆ F₅ )₃ /CPA, thereby inducing the improvement of stereoselectivity.

One-pot synthesis of 3-hydroxy-2-oxindoles via acyloin rearrangements of 2-hydroxy-indolin-3-ones generated in situ from 2-alkynyl arylazides

A novel one-pot method to prepare 3-hydroxy-2-oxindoles via acyloin rearrangements of 2-hydroxy-indolin-3-ones generated in situ from 2-alkynyl arylazides has been described.

Palladium-catalyzed one-pot cycloaddition reactions of thioureas with 3H-indol-3-ones generated in situ from 2-alkynyl arylazides: rapid and efficient access to imidazoloindolines

An efficient palladium-catalyzed one-pot synthesis of imidazoloindolines from 2-alkynyl arylazides under mild reaction conditions has been described.

Highly enantioselective electrosynthesis of C2-quaternary indolin-3-ones

An asymmetric electrosynthesis is developed by combining anodic oxidation and proline-catalysis to realize enantioselective synthesis of C2-quaternary indolin-3-ones from 2-arylindoles.

Synthesis of C2-tetrasubstituted indolin-3-ones via Cu-catalyzed oxidative dimerization of 2-aryl indoles and cross-addition with indoles

An efficient protocol for the synthesis of 2,2-disubstituted indolin-3-ones under mild conditions has been developed. This reaction involves the copper-catalyzed in situ oxidative de-aromatization of 2-arylindoles to indol-3-one, followed by self-dimerization as well as cross-addition with indoles under mild conditions. The result generates a wide variety of C2-tetrasubstituted indolin-3-ones with good to high yields (62–82%).

A general protocol for the synthesis of 2,2-disubstituted indolin-3-ones has been developed through self-dimerization of 2-aryl indoles and cross-addition with indoles under mild Cu-catalyzed oxidative conditions with good to high yields.

Synthesis of tetracyclic indolin-3-ones through Pd-catalyzed intramolecular deacetylative dearomatization of 3-acetoxy-indoles

An efficient palladium-catalyzed intramolecular deacetylative dearomatization reaction of 3-acetoxyindoles has been developed. A range of tetracyclic indolin-3-ones bearing C2-quaternary stereocenters are achieved in good yields, showing a wide substrate scope for this reaction. A preliminary enantioselective reaction is established to furnish the product in 63% ee by using (R,R,R)-phosphoramide-PE as a chiral ligand.

An efficient palladium-catalyzed intramolecular deacetylative dearomatization reaction of 3-acetoxyindoles is disclosed, affording tetracyclic indolin-3-ones bearing C2-quaternary stereocenters in good yields.

Concurrent Asymmetric Reactions Combining Photocatalysis and Enzyme Catalysis: Direct Enantioselective Synthesis of 2,2-Disubstituted Indol-3-ones from 2-Arylindoles

The combination of photoredox and enzymatic catalysis for the direct asymmetric one-pot synthesis of 2,2-disubstituted indol-3-ones from 2-arylindoles through concurrent oxidization and alkylation reactions is described. 2-Arylindoles can be photocatalytically oxidized to 2-arylindol-3-one with subsequent enantioselective alkylation with ketones catalyzed by wheat germ lipase (WGL). The chiral quaternary carbon center at C2 of the indoles was directly constructed. This mode of concurrent photobiocatalysis provides a mild and powerful strategy for one-pot enantioselective synthesis of complex compounds. The experiments proved that other lipases containing structurally analogous catalytic triad in the active site also can catalyze the reaction in the same way. This reaction is the first example of combining the non-natural catalytic activity of hydrolases with visible-light catalysis for enantioselective organic synthesis and it does not require any cofactors.