Catalytic Asymmetric Cyclizative Rearrangement of Anilines and Vicinal Diketones to Access 2,2-Disubstituted Indolin-3-ones

The efficient synthesis of chiral 2,2-disubstituted indolin-3-ones is of great importance due to its significant synthetic and biological applications. However, catalytic enantioselective methods for de novo synthesis of such heterocycles remain scarce. Herein, a novel cyclizative rearrangement of readily available anilines and vicinal diketones for the one-step construction of enantioenriched 2,2-disubstituted indolin-3-ones is presented. The reaction proceeds through a self-sorted [3+2] heteroannulation/regioselective dehydration/1,2-ester shift process. Only chiral phosphoric acid is employed to promote the entire sequence and simplify the manipulation of this protocol. Various common aniline derivatives are successfully applied to asymmetric synthesis as 1,3-binuclephiles for the first time. Remarkably, the observed stereoselectivity is proposed to originate from an amine-directed regio- and enantioselective ortho-Csp2-H addition of the anilines to the ketones. A range of synthetic transformations of the resulting products are demonstrated as well.

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.

Construction of Enantioenriched Quaternary C-Cl Oxindoles through Palladium-Catalyzed Asymmetric Allylic Substitution with Chloroenolates

A palladium-catalyzed asymmetric chloroenolate allylation with vinyl benzoxazinanones under mild reaction conditions has been developed, affording a series of optically active 3,3-disubstituted oxindoles exhibiting a chloro-group and a linear aryl amino side chain in good yields with up to 96% ee. Versatile functional group tolerance on the benzene ring has been demonstrated, and the utility of this method was probed by a scale-up synthesis and highlighted by product derivatizations.

Brønsted Base-Catalyzed Enantioselective α-Functionalization of Carbonyl Compounds Involving π-Extended Enolates

Chiral Brønsted base (BB) catalyzed asymmetric transformations constitute an important tool for synthesis. A meaningful fraction of these transformations proceeds through transiently generated enolate intermediates, which display quite versatile reactivity against a variety of electrophiles. Some years ago, our group became interested in developing BB-catalyzed asymmetric reactions of enolizable carbonyl substrates that involve π-extended enolates in which, besides control of reaction diastereo and enantioselectivity, the site-selectivity control is an additional issue in most cases. In the examples covered in this account the opportunities deployed, and the challenges posed, by these methods are illustrated, with a focus on the generation of quaternary carbon stereocenters. In the way, new bifunctional BB catalysts as well as achiral templates were developed that may find further applications.

Synthesis of Tetrahydro-indolones through Rh(III)-Catalyzed [3 + 2] Annulation of Enaminones with Iodonium Ylides

An unprecedented protocol for a Rh(III)-catalyzed [3 + 2] annulation from simple and readily available enaminones and iodonium ylides has been developed. The novel strategy allows for access to a new class of structurally diverse tetrahydro-indolones with high efficiency and a broad substrate scope. In addition, this transformation represents the first example of the selective Rh(III)-catalyzed alkenyl C-H bond functionalization and annulation of enaminones. Finally, the potential applications of this protocol are demonstrated through gram-scale reaction and late-stage modification.

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.

Catalyst-Assisted Selective Vinylation and Methylallylation of a Quaternary Carbon Center Using tert-Butyl Acetate

The In(OTf)₃-catalyzed α-vinylation of various hydroxy-functionalized quaternary carbon centers using in situ generated isobutylene from tert-butyl acetate is presented as a novel synthetic methodology. Moreover, tert-butyl acetate is a nonflammable feed stock and is a readily available source for the in situ production of vinyl substituents, as demonstrated by the vinylation reaction with quaternary hydroxy/methoxy compounds. Moreover, an excellent selectivity for methylallylation over vinylation was obtained with Ni(OTf)₂ as a catalyst. In the case of peroxyoxindole, methylallyl-functionalized 1,4-benzoxazin-3-one derivatives were formed through the sequential rearrangement of peroxyoxindole followed by the nucleophilic attack by isobutylene. The detailed mechanism for this reaction and rationalization for the selectivity are provided using kinetics and density functional theory studies.

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.

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.

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%).

N-Heterocyclic carbene catalyzed desymmetrization of diols: access to enantioenriched oxindoles having a C3-quaternary stereocenter

Herein, we describe an effective strategy for enantioselective synthesis of oxindoles having a C3-quaternary stereocenter via N-heterocyclic carbene (NHC) catalyzed desymmetrization of diols. The process is based on the catalytic asymmetric transfer acylation of primary alcohols using readily available aldehydes as an acylation agent. The reaction enables easy access to diversely functionalized C3-quaternary oxindoles with excellent enantioselectivity. The synthetic potential of the process is further demonstrated via the preparation of the key intermediate for (-)-esermethole and (-)-physostigmine.

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.

Enantioselective Synthesis of Quaternary Oxindoles: Desymmetrizing Staudinger-Aza-Wittig Reaction Enabled by a Bespoke HypPhos Oxide Catalyst

This paper describes a catalytic asymmetric Staudinger-aza-Wittig reaction of (o-azidoaryl)malonates, allowing access to chiral quaternary oxindoles through phosphine oxide catalysis. We designed a novel HypPhos oxide catalyst to enable the desymmetrizing Staudinger-aza-Wittig reaction through the PIII/PV═O redox cycle in the presence of a silane reductant and an IrI-based Lewis acid. The reaction occurs under mild conditions, with good functional group tolerance, a wide substrate scope, and excellent enantioselectivity. Density functional theory revealed that the enantioselectivity in the desymmetrizing reaction arose from the cooperative effects of the IrI species and the HypPhos catalyst. The utility of this methodology is demonstrated by the (formal) syntheses of seven alkaloid targets: (-)-gliocladin C, (-)-coerulescine, (-)-horsfiline, (+)-deoxyeseroline, (+)-esermethole, (+)-physostigmine, and (+)-physovenine.

β-C-Glycosylation with 2-Oxindole Acceptors via Palladium-Catalyzed Decarboxylative Reactions

This report describes a highly efficient β-selective C-glycosylation of bicyclic galactals with 2-oxindoles through a palladium-catalyzed decarboxylative pathway. A variety of substrates representing both glycosyl donors and acceptors could be transformed in greater than 90% yields under mild reaction conditions. The decarboxylation intermediate of galactal could serve as an efficient base to deprotonate the enol tautomer of 2-oxindole and enhance its nucleophilicity. The β-selective nucleophilic addition at the anomeric center originates from the steric hindrance imposed by the palladium and bulky ligand.

N-Heterocyclic Carbene-Catalyzed [3 + 2] Annulation of 3,3'-Bisoxindoles with α-Bromoenals: Enantioselective Construction of Contiguous Quaternary Stereocenters

An NHC-catalyzed enantio- and diastereoselective [3 + 2] annulation of α-bromoenals with bisoxindoles is developed, affording efficient access to various spirocyclic bisoxindole alkaloids. This protocol tolerates a broad substrates scope, with various spirocyclic bisoxindoles obtained in generally excellent enantioselectivities. More importantly, two contiguous sterically congested all-carbon quaternary stereocenters are successfully created during this process.

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.

Stereoselective synthesis of C3-tetrasubstituted oxindoles via copper catalyzed asymmetric propargylation

Herein, a copper catalyzed asymmetric propargylation of 2-oxindole-3-carboxylate esters with terminal propargylic esters is described. This strategy successfully provides a direct approach to constructing a broad range of chiral C3-tetrasubstituted oxindoles with contiguous tertiary and quaternary carbon stereocenters in high yields and excellent enantioselectivities (16 examples, up to 99% yield and 98% ee). Moreover, the diastereoisomers of the two newly formed stereocenters can be separated by silica gel chromatography, thereby providing a valuable stereoselective access to all four possible stereoisomers of C3-tetrasubstituted oxindoles.

Herein, a copper catalyzed asymmetric propargylation of 2-oxindole-3-carboxylate esters with terminal propargylic esters is described.

Copper-Catalyzed Cyclization/Dimerization of Tryptamines with O2/Air as the Sole Oxidant: Direct Access to Complex Bispyrrolidino[2,3-b]indoline

The first transition metal catalytic one-step synthesis of the 3a, 3a'-bispyrrolidino [2,3-b] indoline scaffold via tandem cyclization/dimerization of tryptamines has been realized with the environmentally friendly O₂/air as the sole oxidant. Different from the traditional direct oxidation of indole "N-H" group by excess amount of metal salts, a copper-catalyzed oxidative cyclization reaction is developed for the formation of the radical pyrrolidinoindoline intermediate in the current strategy. The robustness and practicality of this methodology is demonstrated by the step-economic, divergent total synthesis of natural products (±)-folicanthine and meso-folicanthine.

Construction of sterically congested oxindole derivatives via visible-light-induced radical-coupling

The oxindole scaffold represents an important structural feature in many natural products and pharmaceutically relevant molecules. Herein, we report a visible-light-induced modular methodology for the synthesis of complex 3,3'-disubstituted oxindole derivatives. A library of valuable fluoroalkyl-containing highly sterically congested oxindole derivatives can be synthesized by a catalytic three-component radical coupling reaction under mild conditions (metal & photocatalyst free, >80 examples). This strategy shows high functional group tolerance and broad substrate compatibility (including a wide variety of terminal or non-terminal alkenes, conjugated dienes and enynes, and a broad array of polyfluoroalkyl iodide and oxindoles), which enables modular modification of complex drug-like compounds in one chemical step. The success of solar-driven transformation, large-scale synthesis, and the late-stage functionalization of bioactive molecules, as well as promising tumor-suppressing biological activities, highlights the potential for practical applications of this strategy. Mechanistic investigations, including a series of control experiments, UV-vis spectroscopy and DFT calculations, suggest that the reaction underwent a sequential two-step radical-coupling process and the photosensitive perfluoroalkyl benzyl iodides are key intermediates in the transformation.

A general approach to 2,2-disubstituted indoxyls: total synthesis of brevianamide A and trigonoliimine C

The indoxyl unit is a common structural motif in alkaloid natural products and bioactive compounds. Here, we report a general method that transforms readily available 2-substituted indoles into 2,2-disubstituted indoxyls via nucleophile coupling with a 2-alkoxyindoxyl intermediate and showcase its utility in short total syntheses of the alkaloids brevianamide A (7 steps) and trigonoliimine C (6 steps). The developed method is operationally simple and demonstrates broad scope in terms of nucleophile identity and indole substitution, tolerating 2-alkyl substituents and free indole N-H groups, elements beyond the scope of most prior approaches. Spirocyclic indoxyl products are also accessible via intramolecular nucleophilic trapping.

Base-free enantioselective SN2 alkylation of 2-oxindoles via bifunctional phase-transfer catalysis

N-Protected oxindole derivatives of unprecedented malleability bearing ester moieties at C-3 have been shown to participate in enantioselective phase-transfer-catalysed alkylations promoted by ad-hoc designed quaternary ammonium salts derived from quinine bearing hydrogen-bond donating substituents. For the first time in such phase-transfer-catalysed enolate alkylations, the reactions were carried out under base-free conditions. It was found that urea-based catalysts outperformed squaramide derivatives, and that the installation of a chlorine atom adjacent to the catalyst’s quinoline moiety aided in avoiding selectivity-reducing complications related to the production of HBr in these processes. The influence of steric and electronic factors from both the perspective of the nucleophile and electrophile were investigated and levels of enantiocontrol up to 90% ee obtained. The synthetic utility of the methodology was demonstrated via the concise enantioselective synthesis of a potent CRTH2 receptor antagonist.

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.

Donor-Acceptor Complex Enables Cascade Radical Cyclization of N-Arylacrylamides with Katritzky Salts

Cascade radical cyclization of N-arylacrylamides is an attractive method to prepare 3,3-disubstituted oxindoles. As the reported methods often require additives and/or photocatalysts, we herein report an additive- and photocatalyst-free deaminative strategy for their synthesis under mild conditions, enabled by photoactivation of an electron donor-acceptor (EDA) complex. DFT studies indicated that the involvement of an explicit xylene solvent molecule can greatly enhance the photoactivity of the EDA complex between N-arylacrylamides and Katritzky salts.

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.

I2-Mediated Cross-Dehydrogenative Coupling and Amidation of 3-Aryl Benzofuranones with Aryl Amines for the Synthesis of 3,3-Diaryl Indolin-2-ones

We have developed a protocol for efficient synthesis of indolin-2-ones from benzofuranones and aryl amines using iodine as a mediator. A diverse range of benzofuranones and aryl amines undergo cross-dehydrogenative coupling and amidation of 3-aryl benzofuranones for the cascade reaction to generate products in 24-93% yields. This reaction can be easily scaled-up to give an indolin-2-one in a gram scale. Further chemical manipulation of the products enabled useful transformations of the phenol ring including alkylation, arylation, etc.

Recent advances in cyclization reactions of isatins or thioisatins via C–N or C–S bond cleavage

This review summarizes recent developments on cyclization reactions induced by the C–N or C–S bond cleavage of isatins or thioisatins in the last 5 years, which produce fused products instead of spiro compounds.

Catalytic asymmetric preparation of pyrroloindolines: strategies and applications to total synthesis

Pyrroloindolines are widely present in natural products. In this review, we summarize state-of-the-art of catalytic asymmetric synthesis of pyrroloindolines, as well as related applications to natural products total synthesis.

Ni-Catalyzed asymmetric hetero-Diels–Alder reactions of conjugated vinyl azides: synthesis of chiral azido polycycles

We report herein an efficient Ni(ii)/Feng ligand-catalyzed asymmetric hetero-Diels–Alder reaction between conjugated vinyl azides with carbonyl groups, providing a synthesis of complicated chiral azido polycycles in high yields and excellent enantioselectivities.

Stereoselective synthesis and applications of spirocyclic oxindoles

This review summaries recent synthetic developments towards spirocyclic oxindoles and applications as valuable medicinal and synthetic targets.

Photochemically Induced Ring Opening of Spirocyclopropyl Oxindoles: Evidence for a Triplet 1,3-Diradical Intermediate and Deracemization by a Chiral Sensitizer

The photochemical deracemization of spiro[cyclopropane‐1,3′‐indolin]‐2′‐ones (spirocyclopropyl oxindoles) was studied. The corresponding 2,2‐dichloro compound is configurationally labile upon direct irradiation at λ=350 nm and upon irradiation at λ=405 nm in the presence of achiral thioxanthen‐9‐one as the sensitizer. The triplet 1,3‐diradical intermediate generated in the latter reaction was detected by transient absorption spectroscopy and its lifetime determined (τ=22 μs). Using a chiral thioxanthone or xanthone, with a lactam hydrogen bonding site as a photosensitizer, allowed the deracemization of differently substituted chiral spirocyclopropyl oxindoles with yields of 65–98 % and in 50–85 % ee (17 examples). Three mechanistic contributions were identified to co‐act favorably for high enantioselectivity: the difference in binding constants to the chiral thioxanthone, the smaller molecular distance in the complex of the minor enantiomer, and the lifetime of the intermediate 1,3‐diradical.

Rational drug design, synthesis, and biological evaluation of novel chiral tetrahydronaphthalene-fused spirooxindole as MDM2-CDK4 dual inhibitor against glioblastoma

Simultaneous inhibition of MDM2 and CDK4 may be an effective treatment against glioblastoma. A collection of chiral spirocyclic tetrahydronaphthalene (THN)-oxindole hybrids for this purpose have been developed. Appropriate stereochemistry in THN-fused spirooxindole compounds is key to their inhibitory activity: selectivity differed by over 40-fold between the least and most potent stereoisomers in time-resolved FRET and KINOMEscan® in vitro assays. Studies in glioblastoma cell lines showed that the most active compound ent-4g induced apoptosis and cell cycle arrest by interfering with MDM2 -P53 interaction and CDK4 activation. Cells treated with ent-4g showed up-regulation of proteins involved in P53 and cell cycle pathways. The compound showed good anti-tumor efficacy against glioblastoma xenografts in mice. These results suggested that rational design, asymmetric synthesis and biological evaluation of novel tetrahydronaphthalene fused spirooxindoles could generate promising MDM2-CDK4 dual inhibitors in glioblastoma therapy.

Catalytic enantioselective construction of vicinal quaternary carbon stereocenters

This review summarizes the advances in the catalytic enantioselective construction of vicinal quaternary carbon stereocenters, introduces major synthetic strategies and discusses their advantages and limitations, highlights the application of known protocols in the total synthesis of natural products, and outlines the synthetic opportunities.

This review summarizes the advances in catalytic enantioselective construction of vicinal quaternary carbon stereocenters, introduces major synthetic strategies and discusses their advantages and limitations, and outlines the synthetic opportunities.

Visible-Light-Induced Palladium-Catalyzed Generation of Aryl Radicals from Aryl Triflates

A mild visible-light-induced Pd-catalyzed intramolecular C-H arylation of amides is reported. The method operates by cleavage of a C(sp2 )-O bond, leading to hybrid aryl Pd-radical intermediates. The following 1,5-hydrogen atom translocation, intramolecular cyclization, and rearomatization steps lead to valuable oxindole and isoindoline-1-one motifs. Notably, this method provides access to products with readily enolizable functional groups that are incompatible with traditional Pd-catalyzed conditions.

Light-Triggered Catalytic Asymmetric Allylic Benzylation with Photogenerated C-Nucleophiles

Herein is reported the asymmetric allylic benzylation of Morita–Baylis–Hillman (MBH) carbonates with 2-methylbenzophenone (MBP) derivatives as nonstabilized photogenerated C-nucleophiles. The dual activation of both reaction partners, chiral Lewis-base activation of the electrophile and light activation of the nucleophile, enables the stereoselective installation of benzyl groups at the allylic position to forge tertiary and quaternary carbon centers.

Oxidative cyanation of 2-oxindoles: formal total synthesis of (±)-gliocladin C

Efficient oxidative direct cyanations of 3-alkyl/aryl 2-oxindoles using Cyano-1,2-BenziodoXol-3(1H)-one (CBX) (2a) have been reported under 'transition metal-free' conditions to synthesize a wide variety of 3-cyano 3-alkyl/aryl 2-oxindoles sharing an all-carbon quaternary center under additive-free conditions. The application of this process is shown by the formal total synthesis of (±)-gliocladin C (11c) in a few steps.

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.