Facile and General Synthesis of Quaternary 3-Aminooxindoles

Synthesis of ɑ-Aryl-oxindoles via Grignard Reaction with Isatin in the Presence of Diphenyl Phosphite

A protocol has been developed for the synthesis of α-aryl-oxindoles from isatin and Grignard reagents in the presence of diphenyl phosphite for the first time. This reaction was conveniently carried out under mild conditions in a one-pot fashion with moderate to excellent yields.

A highly efficient method to access unprotected C-3 bifunctional quaternary 3-allyl-3-(amino)oxindoles

A highly efficient Rh(II) catalyzed non-radical protocol to access NH-free C-3 bifunctional oxindoles, which possess 3-allyl and 3-amino simultaneously, was first achieved by employing an intermolecular [2,3]-sigmatropic rearrangement reaction between diazooxindoles and tertiary allylic amines. Utilizing readily available allylamines as the nitrogen and allyl source concurrently, a wide range of bio-active 3-allyl-3-(amino)oxindoles were obtained in excellent yields under very mild reaction conditions; meanwhile, the TON can be up to 90 000. Our study addresses a gap in the literature by investigating intermolecular rearrangements of ammonium ylides with diazoamides, which have been relatively understudied.

Enantioselective Benzylation and Allylation of a Crucial Synthon of 3-Amino Oxindole Schiff Base Promoted by a Cinchonidinium Phase Transfer Catalyst to Enable the Effective Preparation of Chiral Quaternary 3-Amino Oxindoles

3-Amino oxindole Schiff base has been used as an efficient and crucial synthon for highly enantioselective benzylation and allylation with benzyl bromides and allyl bromides in the presence of a 1,3-bis[O(9)-allylcinchonidinium-N-methyl]-2-fluorobenzene dibromide phase transfer catalyst under mild reaction conditions. A broad series of chiral quaternary 3-amino oxindoles were smoothly obtained in good to excellent yields with excellent enantioselectivities (up to 98% ee) with broad substrate generality. A typical scale-up preparation and subsequent Ullman coupling reaction were also smoothly performed, and a special and important chiral spirooxindole benzofuzed pyrrol scaffold with potential pharmaceutical and organocatalytic activities was successfully obtained.

Transition-metal-free oxindole synthesis: quinone-K2CO3 catalyzed intramolecular radical cyclization

A novel and highly efficient transition-metal-free approach for the conversion of α-bromoanilides to 3,3-disubstituted oxindoles is described. This transformation is promoted by catalytic amount of 9,10-phenanthrenequinone (PQ) together with K2CO3,...

N-Heterocyclic carbene complexes enabling the α-arylation of carbonyl compounds

The considerable importance of α-arylated carbonyl compounds, which are widely used as final products or as key intermediates in the pharmaceutical industry, has prompted numerous research groups to develop efficient synthetic strategies for their preparation in recent decades. In this context, the α-arylation of carbonyl compounds catalyzed by transition-metal complexes have been particularly helpful in constructing this motif. As illustrated in this contribution, tremendous advances have taken place using palladium- and nickel-NHC (NHC = N-heterocyclic carbene) complexes as pre-catalysts for the arylation of a wide range of ketones, aldehydes, esters and amides with electron-rich, electron-neutral, electron-poor, and sterically hindered aryl halides or pseudo-halides. Despite significant progress, especially in asymmetric α-arylations promoted by chiral NHC ligands, there are numerous challenges which have and continue to encourage further studies on this topic. Some of these are presented in this report.

Thermal-mediated catalyst-free heterolytic cleavage of 3-halooxindoles: rapid access to 3-functionalized-2-oxindoles

Herein a previously unreported catalyst-free S_N1 reaction of the 3-halooxindoles to build 3-functionalized-2-oxindoles is described.

CBr4-mediated cross-coupling reactions of α-amino carbonyl compounds with alcohols and thiols to build C–O and C–S bonds, respectively

The direct C(sp³)–H bond functionalization of α-amino carbonyl compounds with CBr₄ to construct C–O and C–S bonds.

Alcohols as Substrates and Solvents for the Construction of 3-Alkoxylated-2-Oxindoles by Direct Alkoxylation of 3-Halooxindoles

Described herein is an environmentally benign method for the synthesis of multisubstituted 3-alkoxylated-2-oxindoles 3 via direct alkoxylation of 3-halooxindoles 1. A wide variety of such multisubstituted 3-alkoxylated-2-oxindole scaffolds were smoothly obtained in good yields (up to 94%) by heating in an oil bath at 35 °C for 24 h. A particularly valuable feature of this method was the development of environment-friendly chemistry using alcohols 2 as both the substrates and solvents in the presence of a catalytic amount of base.

Synthesis of oxindole from acetanilide via Ir(iii)-catalyzed C–H carbenoid functionalization

The Ir(iii)-catalyzed intermolecular C–H annulations of acetanilide with diazotized Meldrum's acid furnished the oxindole derivative. Brief synthetic applications of the synthesized oxindole were also demonstrated.

Highly efficient synthesis of chiral quaternary 3-aminooxindoles promoted by zinc(ii) chloride via Et2Zn-catalysed addition of Grignard reagents to isaltin-derived N-tert-butanesulfinyl ketimines

An approach to chiral quaternary 3-aminooxindoles via Et₂Zn catalyzed diastereoselective addition of various Grignard reagents to broad isaltin-derived N-tert-butanesulfinyl ketimines promoted by zinc(ii) chloride.

Iron-catalyzed direct α-arylation of α-amino carbonyl compounds with indoles

A mild and general α-arylation of α-amino carbonyls with indoles catalyzed by Fe(ClO4)3 has been developed. C-H activation is smoothly fulfilled by using TBHP as the oxidant with good yields. Two hydrogen dissociations make this transformation more environmentally benign because of high atom efficiency.

A convergent, umpoled synthesis of 2-(1-amidoalkyl)pyridines

A convenient, one-pot, two-component synthesis of 2-(1-amidoalkyl)pyridines is reported, based upon the substitution of suitably-activated pyridine N-oxides by azlactone nucleophiles, followed by decarboxylative azlactone ring-opening. The synthesis obviates the need for precious metal catalysts to achieve a formal enolate arylation reaction, and constitutes a formally ‘umpoled’ approach to this valuable class of bioactive structures.

3-Alkyl-3-(alkylamino)indolin-2-ones via Base-Mediated C-Arylation of 2-Nitrobenzenesulfonamides

Resin-bound intermediates prepared from polymer-supported amino acid esters, 2-nitrobenezenesulfonyl chlorides, and alcohols were used to synthesize 3-alkyl-3-(alkylamino) indolin-2-ones. The key step of the reaction sequence was the formation of a quaternary carbon via the base-mediated C-arylation of 2-nitrobenzenesulfonamides. The cleavage of the acyclic precursors from the resin and subsequent reduction of the nitro group by Zn in acetic acid triggered the spontaneous cyclization of the arylated compounds to indolinones. The synthesis was carried out using simple commercially available building blocks under mild conditions and provided the 3,3-disubstituted indolinone derivatives with good overall yields however, the arylation reaction resulted in the epimerization of the quaternary carbon.

TBHP mediated oxidation of N-2-alkynylphenyl α-amino carbonyl compounds to oxalic amides using visible light photoredox catalysis and their application in the synthesis of 2-aryl indoles

Visible light promoted the oxidation of compounds 1 to amides 2 which were easily transferred to compounds 12.

Assembly of 3-allyl-3-ethynyl-oxindole motifs via palladium(ii)-catalyzed quaternary allylation of 3-ethynyl-3-OBoc-oxindoles

A simple and efficient strategy for the synthesis of 3-allyl-3-ethynyl-oxindoles using Pd(ii) catalyst has been developed. Applications of these intermediates were realized by synthesizing structurally diverse carbocyclic spirooxindoles.

Copper-catalyzed oxidative oxyalkylation of enol ethers with α-amino carbonyl compounds and hydroperoxides

The first example of alkene oxyalkylation through C(sp³)–H functionalization is described for the synthesis of 2-amino-3,4-dioxy carbonyl compounds.

Highly enantioselective synthesis of bisoxindoles with two vicinal quaternary stereocenters via Lewis base mediated addition of oxindoles to isatin-derived ketimines

A highly efficient method provides access to the bisoxindole structure moiety with two vicinal quaternary stereogenic centers (>99 : 1 dr, >99% ee).

Rotational isomers of N-methyl-N-arylacetamides and their derived enolates: implications for asymmetric Hartwig oxindole cyclizations

The rotational preferences of N-(2-bromo-4,6-dimethylphenyl)-N-methyl 2-phenylpropanamide were studied as a model of precursors for Hartwig asymmetric oxindole cyclizations. The atropisomers of this compound were separated by flash chromatography, and then the enantiomers were resolved and the interconversions of the stereocenter and the N-Ar axis were studied. Under thermal conditions, the axis is very stable. Under the basic conditions of the Hartwig cyclization, both the stereocenter and the chiral axis equilibrate via enolate formation. The N-Ar rotation barrier of a 2-phenylacetamide analogue was reduced from 31 kcal mol(-1) in the precursor to 17 kcal mol(-1) in the enolate. Reasons for this dramatic barrier reduction and implications of both N-Ar and amide C-N rotations for Hartwig cyclizations are discussed.

Direct α-arylation of α-amino carbonyl compounds with indoles using visible light photoredox catalysis

A general and mild method for the construction of functionalized 2-(1H-indol-3-yl)-2-amino-carbonyl compounds was achieved, which represents the first example of direct α-arylation of α-amino carbonyl compounds with indoles using the visible light photoredox catalysis strategy.