Alpha-arylation of 3-aryloxindoles

Enantioselective construction of triaryl-substituted all-carbon quaternary stereocenters via organocatalytic arylation of oxindoles with azonaphthalenes

Azonaphthalenes have been verified as a class of effective arylation reagents in a variety of asymmetric transformations. Here a highly efficient approach to construct triaryl-substituted all-carbon quaternary stereocenters through chiral phosphoric acid-catalyzed enantioselective arylation of 3-aryl-2-oxindoles with azonaphthalenes is disclosed. This chemistry is scalable and displays excellent functional group tolerance, furnishing a series of 3,3-disubstituted 2-oxindole derivatives in good yields with excellent enantiocontrol. Preliminary mechanistic data suggest that the initially formed direct addition intermediate undergoes intramolecular annulation under acidic reaction conditions.

Iron-Catalyzed Oxidative Cross-Coupling of Phenols and Tyrosine Derivatives with 3-Alkyloxindoles

In this study, a novel iron-catalyzed oxidative cross-coupling reaction between phenols and 3-alkyloxindole derivatives is reported. The efficient method, which is based on the FeCl₃ catalyst and the t-BuOOt-Bu oxidant in 1,2-dichloroethane at 70 °C, affords 3-alkyl-3-(hydroxyaryl)oxindole compounds with a high degree of selectivity. The generality of the conditions was proven by reacting various substituted phenols, naphthols, and tyrosine derivatives with 3-alkyloxindoles. To apply the chemistry for the conjugation of tyrosine-containing short peptides with oxindolylalanine (Oia) derivatives, the reaction conditions were modified [Fe(O₂CCF₃)₃ catalyst, t-BuOOt-Bu, HFIP, 70 °C], and amino acids with acid-stable N-protecting groups were used.

Silyl Cyanopalladate-Catalyzed Friedel–Crafts-Type Cyclization Affording 3-Aryloxindole Derivatives

3-Aryloxindole derivatives were synthesized through a Friedel–Crafts-type cyclization. The reaction was catalyzed by a trimethylsilyl tricyanopalladate complex generated in situ from trimethylsilyl cyanide and Pd(OAc)2. Wide varieties of diethyl phosphates derived from N-arylmandelamides were converted almost quantitatively into oxindoles. When N,N-dibenzylamide was used instead of an anilide substrate, a benzo-fused δ-lactam was obtained. An oxindole product was subjected to substitution reactions to afford 3,3-diaryloxindoles with two different aryl groups.

Palladium-Catalyzed Construction of Quaternary Stereocenters by Enantioselective Arylation of γ-Lactams with Aryl Chlorides and Bromides

Herein, we report the first Pd-catalyzed enantioselective arylation of α-substituted γ-lactams. Two sets of conditions were developed for this transformation, allowing for the use of either aryl chlorides or bromides as electrophiles. Utilizing a highly electron-rich dialkylphosphine ligand we have been able to construct α-quaternary centers in good yields (up to 91 % yield) and high enantioselectivities (up to 97 % ee).

Transition-metal-free α-arylation of oxindoles via visible-light-promoted electron transfer

An operationally simple photochemical strategy for the direct arylation of oxindoles with (hetero)aryl halides in the absence of both transition metals and photoredox catalysts has been developed. The reaction provides an efficient way to construct various 3-aryloxindole building blocks of pharmaceutical interest at ambient temperature by using household compact fluorescent light (CFL) bulbs as the light source. Preliminarily, mechanistic studies revealed that the intermolecular electron transfer relied on the formation of photon-absorbing electron-donor-acceptor (EDA) complexes between electron-rich oxindole enolates and electron-deficient (hetero)aryl halides, and a radical chain mechanism was operative.

Palladium(II)/N-Heterocyclic Carbene Catalyzed One-Pot Sequential α-Arylation/Alkylation: Access to 3,3-Disubstituted Oxindoles

Rationally designed fluorene-based mono- and bimetallic Pd-PEPPSI complexes were synthesized and demonstrated to be effective for the one-pot sequential α-arylation/alkylation of oxindoles. This streamlined approach offers efficient access to functionalized 3,3-disubstituted oxindoles in excellent yields (up to 89%) under mild reaction conditions.

A Palladium-Catalyzed α-Arylation of Oxindoles with Aryl Tosylates

A palladium-catalyzed monoselective C3 arylation of 2-oxindoles with aryl tosylates is described. With the Pd/CM-phos catalyst system, the corresponding 3-arylated oxindoles can be obtained in good to excellent yields (≤97%). The reaction conditions are mild (using 0.5 mol % Pd in general and KF as a base), and functional groups such as methyl ester, NH amido, and enolizable keto moieties are found to be compatible.

Transition-metal-free Chemoselective Oxidative C-C Coupling of the sp3 C-H Bond of Oxindoles with Arenes and Addition to Alkene: Synthesis of 3-Aryl Oxindoles, and Benzofuro- and Indoloindoles

A transition-metal (TM)-free and halogen-free NaOtBu-mediated oxidative cross-coupling between the sp³ C-H bond of oxindoles and sp² C-H bond of nitroarenes has been developed to access 3-aryl substituted and 3,3-aryldisubstituted oxindoles in DMSO at room temperature in a short time. Interestingly, the sp³ C-H bond of oxindoles could also react with styrene under TM-free conditions for the practical synthesis of quaternary 3,3-disubstituted oxindoles. The synthesized 3-oxindoles have also been further transformed into advanced heterocycles, that is, benzofuroindoles, indoloindoles, and substituted indoles. Mechanistic experiments of the reaction suggests the formation of an anion intermediate from the sp³ C-H bond of oxindole by tert-butoxide base in DMSO. The addition of nitrobenzene to the in-situ generated carbanion leads to the 3-(nitrophenyl)oxindolyl carbanion in DMSO which is subsequently oxidized to 3-(nitro-aryl) oxindole by DMSO.

An efficient Friedel–Crafts alkylation for the synthesis of 3-indolyl-3-hydroxy oxindoles and unsymmetrical 3,3-diaryl oxindoles catalyzed by Dabco-based ionic liquids in water

An efficient, green and reusable catalytic system for controlled 3-indolylation of isatins.

Regioselective synthesis of 3-anthracenyloxindoles and 3-carbazolyloxindoles by indium(iii)-catalyzed direct arylation and their fluorescent chemosensor properties

An efficient protocol for diverse 3-anthracenyloxindoles and 3-carbazolyloxindoles has been developed by In(OTf)₃-catalyzed direct arylation of 3-diazooxindoles with anthracenes or carbazoles.

Efficient synthesis of 3H-indoles enabled by the lead-mediated α-arylation of β-ketoesters or γ-lactams using aryl azides

The development of a lead-mediated α-arylation reaction between aryl azides and β-ketoesters or γ-lactams that facilitates the formation of 3H-indoles is disclosed. Twenty-five examples are included which demonstrate the generality of this reaction to access aryl azides bearing tetrasubstituted o-alkyl substituents. When paired with a Staudinger reduction, this reaction streamlines the synthesis of functionalized 3H-indoles.

Preparation of Aryl-Susbstituted 2-Oxyindoles by Superelectrophilic Chemistry

A series of pyridyl-substituted 3-hydroxy-2-oxyindoles have been prepared and reacted with arenes in superacid promoted Friedel-Crafts reactions. The product aryl-substituted 2-oxyindoles are formed in generally good yields. With substituted arenes such as toluene, bromobenzene, or ethyl salicylate, the Friedel-Crafts reactions occur with excellent regioselectivity. A mechanism is proposed involving dicationic, superelectrophilic species leading to the electrophilic aromatic substitution chemistry.

Organocatalytic asymmetric Michael addition of unprotected 3-substituted oxindoles to 1,4-naphthoquinone

We reported the first example of organocatalytic Michael addition of unprotected 3-prochiral oxindoles 1 to 1,4-naphthoquinone. Quinidine derivative (DHQD)₂PYR was found to be able to catalyze this reaction in up to 83% ee, with moderate to excellent yields. This method could be used for the synthesis of enantioenriched 3,3-diaryloxindoles, and the catalytic synthesis of which was unprecedented.