Total Synthesis of (±)-Grandilodine B

B(C6F5)3/CPA-Catalyzed Aza-Diels-Alder Reaction of 3,3-Difluoro-2-Aryl-3H-indoles and Unactivated Dienes

Here we report B(C6F5)3/CPA-catalyzed enantioselective aza-Diels-Alder reaction of 3,3-difluoro-2-Aryl-3H-indoles with unactivated dienes to access chiral 10,10-difluoro-tetrahydropyrido[1,2-a]indoles. This protocol allows the formation of pyrazole-based C2-quaternary indolin-3-ones with high enantioselectivities and regioselectivities. Moreover, gram-scale synthesis of the 10,10-difluoro-tetrahydropyrido[1,2-a]indole skeleton was successfully achieved without any reduction in both yield and enantioselectivity.

Oxidative Transformation of 2-Furylanilines into Indolin-3-ones

Oxidation of 2-furylaninlies with m-CPBA followed by treatment with a base provides access to functionalized indolin-3-ones. The designed oxidative transformation utilizes an underassessed chemical behavior of furyl-containing amines to form a C-N bond via engaging a β-carbon atom of the furan core upon a ring-forming step, thereby providing an alternative disconnection toward nitrogen-containing heterocycles.

Isatogenols as Precursors for the Synthesis of Fully Substituted Indolines through Regio- and Stereoselective [3 + 2] Cycloaddition Using Various Olefins

Here, we describe a unique reactivity of isatogen derivatives bearing a hydroxy group at the C3-position (isatogenol) and their synthetic application to highly regio- and stereoselective [3 + 2] cycloaddition reactions. This method provides facile access to polyfused and highly functionalized heterocycles including consecutive stereocenters. Furthermore, DFT calculations revealed that hydrogen bonding is a key to controlling the regio- and stereoselectivity in the cycloaddition using acrylates.

Enantioselective Synthesis of C2-Quaternary Indolin-3-ones by Pt-Catalyzed Alkynylation of 2-Aryl-3H-indol-3-one with Alkynylsilanes

An efficient method for the synthesis of five-membered chiral propargylic amines from 2-aryl-3H-indol-3-one and alkynylsilanes has been developed. The reaction proceeded under the catalytic system of PtCl4, oxazoline-based ligand L11, Zn(CF3COO)2, and AcOH in DCE at 95 °C via in situ desilylation of TMS-alkynes. This methodology also highlights a new protocol for the in situ desilylation of alkynylsilanes. The reaction showed a broad substrate scope with good yields and enantioselectivity.

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.

Catalyst-Free gem-Difluorination/Spirocyclization of Indole-2-carboxamides: Synthesis of C2-Spiroindoline Derivatives

A catalyst-free gem-difluorination/spirocyclization reaction has been successfully developed for the synthesis of gem-difluorinated C2-spiroindoline derivatives from indole-2-carboxamides. The resulting gem-difluorinated C2-spiroindolines can be easily converted into 2-spiropseudoindoxyls through hydrolysis. This method offers the benefits of simple operation, convenient access to raw materials, and mild conditions. Dual function of Selectfluor in this reaction is noteworthy as it can serve as both a fluorinating agent and an alkaline accelerator precursor.

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.

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%).

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.

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.

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.

Synthesis of Hydroxysuccinimide Substituted Indolin-3-ones via One-Pot Cascade Reaction of o-Alkynylnitrobenzenes with Maleimides under Au(III)-Cu(II) Relay/Synergetic Catalysis

Presented herein is a one-pot cascade reaction of o-alkynylnitrobenzenes with maleimides leading to the formation of hydroxysuccinimide substituted indolin-3-ones under Au(III)-Cu(II) relay/synergetic catalysis. Mechanistically, the formation of the title products involves an unprecedented cascade process including (1) nitro-alkyne cycloisomerization of o-alkynylnitrobenzene to give isatogen; (2) [3 + 2] dipolar cycloaddition of isatogen with maleimide; and (3) ring opening of the in situ formed isoxazolidine moiety under neutral conditions. Notably, a wide range of substrates bearing various functional groups are compatible with the reaction conditions to give a series of highly valuable hybrid compounds in good efficiency with excellent atom economy. In addition, the products thus obtained could be easily transformed into the corresponding maleimide substituted indolin-3-ones. Importantly, some products demonstrated significant antiproliferative activity in human cancer cell lines.

Lewis acid mediated cyclization: synthesis of 2 spirocyclohexylindolines

Herein, we report the synthesis of 2-spirocyclohexylindolines based on a Lewis acid mediated cyclization. This diastereoselective procedure provides the target structures in a straightforward way via dual activation.

Synthesis of indoline-fused eight-membered azaheterocycles through Zn-catalyzed dearomatization of indoles and subsequent base-promoted C-C activation

A cascade reaction involving the Zn-catalyzed dearomatization of indoles, base-promoted ring-expansion and intramolecular S_NAr reaction has been developed. This process realized a novel, atom economical and efficient synthesis of indoline-fused eight-membered azaheterocycles in a one pot manner.

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.

Oxidative Dearomative Cross-Dehydrogenative Coupling of Indoles with Diverse C-H Nucleophiles: Efficient Approach to 2,2-Disubstituted Indolin-3-ones

The oxidative, dearomative cross-dehydrogenative coupling of indoles with various C-H nucleophiles is developed. This process features a broad substrate scope with respect to both indoles and nucleophiles, affording structurally diverse 2,2-disubstituted indolin-3-ones in high yields (up to 99%). The oxidative dimerization and trimerization of indoles has also been demonstrated under the same conditions.

Intramolecular trapping of ammonium ylides with N-benzoylbenzotriazoles in aqueous medium: direct access to the pseudoindoxyl scaffold

The present work documents an operationally simple, clean and practical method for accessing the 2,2-disubstituted indolin-3-one (pseudoindoxyl) scaffold. The rhodium carbenoid mediated reaction between N-o-alkylamino benzoylbenzotriazoles and aryl diazoacetates occurs smoothly in water and exploits the leaving group ability of the benzotriazole moiety to install the carbonyl function in the product. Other highlights of the methodology are a wide substrate scope and experimental practicality given the re-use of the benzotriazole byproduct for starting material preparation.

Direct oxidative dearomatization of indoles: access to structurally diverse 2,2-disubstituted indolin-3-ones

Described is an efficient oxidative dearomatization of indoles with TEMPO oxoammonium salt and a broad range of nucleophiles.

Recent advances in the synthesis of C2-spiropseudoindoxyls

This review summarizes the recent development of novel approaches to construct structurally unique oxindoles featuring a spirocycle at the C2 position.

Synthesis of 1 H-Pyrrol-3(2 H)-ones via Three-Component Reactions of 2,3-Diketo Esters, Amines, and Ketones

An efficient one-pot, three-component reaction of 2,3-diketo esters with amines and ketones has been developed for the synthesis of 1 H-pyrrol-3(2 H)-ones. By using trifluoroacetic acid (TFA) as the additive and acetonitrile (MeCN) as the solvent, this convenient method provides a library of 1 H-pyrrol-3(2 H)-ones in moderate to good yields. The simple protocol features readily available starting materials, a straightforward process, good functional group tolerance, and broad substrate scope.

Organocatalytic Asymmetric Cascade Aerobic Oxidation and Semipinacol Rearrangement Reaction: A Visible Light-Induced Approach to Access Chiral 2,2-Disubstituted Indolin-3-ones

An enantioselective cascade aerobic oxidation and semipinacol rearrangement reaction of 2-aryl-3-alkyl-substituted indoles via visible-light-driven cooperative organophotoredox and H-bonding catalysis is reported. The current method provides an expedient and sustainable approach to furnish a variety of valuable chiral 2-aryl-2-alkyl-substituted indolin-3-ones in 64-90 % yield with 58-94 % ee. Preliminary control experiments present important insights into the stereochemistry.

Unified Total Synthesis of Pyrroloazocine Indole Alkaloids Sheds Light on Their Biosynthetic Relationship

The total synthesis of seven members of the lapidilectine and grandilodine family of alkaloids has been accomplished in racemic and enantiopure form without protection/deprotection of functional groups. The two key steps, an 8- endo-dig hydroarylation and a 6- exo-trig photoredox cyclization, were catalyzed using gold. A rationale for the formation of the cyclopropane ring of the lundurines is also provided.

Total syntheses of pyrroloazocine indole alkaloids: challenges and reaction discovery

Total syntheses of pyrroloazocine indole alkaloids (lapidilectines, grandilodines, lundurines and tenuisines) are discussed in terms of existing retrosynthetic solutions and novel reaction discoveries.

Chiral phosphoric acid-catalyzed direct asymmetric mannich reaction of cyclicC-acylimines with simple ketones: facile access to C2-quaternary indolin-3-ones

A chiral Brønsted acid-catalyzed direct asymmetric Mannich reaction of simple ketones with cyclicC-acylimines has been established for the synthesis of C2-quaternary indolin-3-ones.

Palladium-catalyzed direct C(sp3)–H arylation of indole-3-ones with aryl halides: a novel and efficient method for the synthesis of nucleophilic 2-monoarylated indole-3-ones

A novel and efficient method for the synthesis of nucleophilic 2-monoarylated indole-3-ones via palladium-catalyzed direct C(sp³)–H arylation of indole-3-ones with aryl halides has been developed.

Facile access to 2,2-disubstituted indolin-3-ones via a cascade Fischer indolization/Claisen rearrangement reaction

From readily accessible arylhydrazines and allyloxyketones, 2,2-disubstituted indolin-3-ones could be obtained in good to excellent yields via a cascade Fischer indolization/Claisen rearrangement process.