Palladium-Catalyzed Intramolecular 5-exo-dig Hydroarylations of N-Arylpropiolamides: Thermodynamics-Controlled Stereoselective Synthesis of 3-Methyleneoxindoles

The Assembly of Cerium(III)-Containing Silicotungstate with Lewis Acid-Base Sites Enables the Selective C3-Alkenylation of Oxindole

A cerium(III)-containing silicotungstate, [H2N(CH3)2]10NaK[KCe(SiW11O39)2(H2O)]·18.5H2O (CeSiW), was successfully synthesized and characterized. Structure analysis reveals that CeSiW is composed of two {SiW11O39} units connected by one cerium(III) cation to form a typical 1:2 sandwich structure, which is further expanding into a 1D chain linked by K+ ions. The oxygen-enriched surfaces of {SiW11O39} units and open cerium sites provide abundant Lewis base and acid sites in CeSiW. As a result, CeSiW efficiently catalyzed the C3-alkenylation of oxindoles with aldehydes through the simultaneous activation of both reaction substrates on its crystal framework. Various 3-benzylidene-oxindoles are synthesized with excellent yields and high E-selectivity under solvent-free conditions.

Is It Possible to Obtain a Product of the Desired Configuration from a Single Knoevenagel Condensation? Isomerization vs. Stereodefined Synthesis

The biological activity of compounds directly depends on the three-dimensional arrangement of affinity fragments since a high degree of pharmacophore compliance with the binding site is required. 3-Benzylidene oxindoles are privileged structures due to their wide spectrum of biological activity, synthetic availability, and ease of modification. In particular, both kinase inhibitors and kinase activators can be found among 3-benzylidene oxindoles. In this work, we studied model compounds obtained via oxindole condensation with aldehydes and alkylphenones. These condensation products can exist in the form of E- and Z-isomers and also undergo isomerization in solutions. The factors causing isomeric transformation of these compounds were established. Comparative kinetic studies to obtain quantitative characteristics of UV-driven isomerization were first performed. The results obtained indicate dramatic differences in two subclasses, which should be considered when developing biologically active molecules.

Transient Chelating Group-Controlled Stereoselective Rh(I)-Catalyzed Silylative Aminocarbonylation of 2-Alkynylanilines: Entry to (Z)-3-(Silylmethylene)indolin-2-ones

A new, mild acryl transient chelating group-controlled stereoselective Rh(I)-catalyzed silylative aminocarbonylation of 2-alkynylanilines with CO and silanes for producing (Z)-3-(silylmethylene)indolin-2-ones is presented. By using an acryl transient chelating group 2-alkynylanilines...

Yb(OTf)3 catalyzed [1,3]-rearrangement of 3-alkenyl oxindoles

A Yb(OTf)₃ catalyzed [1,3]-rearrangement of 3-alkenyl oxindoles was achieved, affording a variety of multifunctional 3-ylideneoxindoles with good yields and Z/E selectivities (64%-89% yield, 78 : 22->99 : 1 Z/E). Importantly, an operationally simple, one-pot sequential catalytic synthesis of 3-ylideneoxindoles was also developed. Additionally, a cross [1,3]-rearrangement experiment and nonracemic transformation were also carried out, which indicated a concerted rearrangement mechanism of this methodology.

E-Z isomerization of 3-benzylidene-indolin-2-ones using a microfluidic photo-reactor

Here, we report controlled E-Z isomeric motion of the functionalized 3-benzylidene-indolin-2-ones under various solvents, temperature, light sources, and most importantly effective enhancement of light irradiance in microfluidic photoreactor conditions. Stabilization of the E-Z isomeric motion is failed in batch process, which might be due to the exponential decay of light intensity, variable irradiation, low mixing, low heat exchange, low photon flux etc. This photo-μ-flow light driven motion is further extended to the establishment of a photostationary state under solar light irradiation.

Controlling alkyne reactivity by means of a copper-catalyzed radical reaction system for the synthesis of functionalized quaternary carbons

A terminal alkyne is one of the most useful reactants for the synthesis of alkyne and alkene derivatives. Because an alkyne undergoes addition reaction at a C-C triple bond or cross-coupling at a terminal C-H bond. Combining those reaction patterns could realize a new reaction methodology to synthesize complex molecules including C-C multiple bonds. In this report, we found that the reaction of 3 equivalents of terminal alkyne 1 (aryl substituted alkyne) and an α-bromocarbonyl compound 2 (tertiary alkyl radical precursor) undergoes tandem alkyl radical addition/Sonogashira coupling to produce 1,3-enyne compound 3 possessing a quaternary carbon in the presence of a copper catalyst. Moreover, the reaction of α-bromocarbonyl compound 2 and an alkyne 4 possessing a carboxamide moiety undergoes tandem alkyl radical addition/C-H coupling to produce indolinone derivative 5.

When Ethyl Isocyanoacetate Meets Isatins: A 1,3-Dipolar/Inverse 1,3-Dipolar/Olefination Reaction for Access to 3-Ylideneoxindoles

A new CuI/1,10-phen-catalyzed reaction for the synthesis of 3-ylideneoxindoles from readily available isatins and ethyl isocyanoacetate, in which ethyl isocyanoacetate acts as a latent two-carbon donor like the Wittig reagent, is reported. A tandem procedure including 1,3-dipolar cycloaddition/inverse 1,3-dipolar ring opening/olefination allows the preparation of 3-ylideneoxindoles with broad functional group tolerance.

Palladium-catalyzed dimerization of N-aryl propargylamines for the synthesis of 3-vinylquinolines

A straightforward method for the synthesis of polyfunctionalized quinolines from readily available N-aryl propargylamines under aerobic conditions was developed. It provides convenient access to a variety of synthetically and pharmaceutically important quinolines in moderate to good yields. Control experiments suggest that the cascade reaction might proceed via the Pd-catalyzed electrophilic cyclization of N-aryl propargylamines followed by a hydroarylation process through trapping of the σ-quinolinylpalladium intermediate with a second molecule of the substrate.

Hydroarylation of 2-Aryloxybut-1-en-3-ynes via Pd/Acid-Catalyzed C-H Bond Activation: A Concise Synthesis of 2,3-Bismethylene-2,3-dihydrobenzofurans

An intramolecular exo-hydroarylation of 2-aryloxy-1,4-disilylbut-1-en-3-ynes via ortho-C-H bond activation under palladium(0) and acid catalysis was found to give 2,3-bis(silylmethylidene)-2,3-dihydrobenzofurans. The two silyl groups present probably promoted the reaction and played a key role in stabilizing the diene moiety in the product. The products readily led to functionalized condensed cycles by a Diels-Alder reaction.

A Regioselective Synthesis of 6-Alkyl- and 6-Aryluracils by Cs2CO3- or K3PO4-Promoted Dimerization of 3-Alkyl- and 3-Aryl-2-Propynamides

A regioselective synthesis of 6-alkyl- and 6-aryluracils was developed by the dimerization of 3-alkyl- and 3-aryl-2-propynamides promoted by either Cs₂CO₃ or K₃PO₄. A range of 3-aryl-2-propynamides, with both electron-deficient and electron-rich 3-aryl substituents, were successfully reacted in high yields. Cs⁺ acts as a soft Lewis acid to polarize the carbon-carbon triple bond, and solid K₃PO₄ interacts with carbonyl oxygen, promoting intermolecular nucleophilic attack by the only weakly nucleophilic amide nitrogen. Experiments were conducted to support the proposed mechanism.

Gold-Catalyzed Hydroarylation of N-Aryl Alkynamides for the Synthesis of 2-Quinolinones

A mild method for the synthesis of 2-quinolinones via hydroarylation of N-aryl alkynamides is reported. While traditional methods have relied on the use of strong Brønsted or Lewis acids, this report describes the development of mild reaction conditions that yield 2-quinolinones in good to excellent yield using a commercially available gold catalyst. Substrates bearing a variety of functional groups are presented, with N-substitution proving to be key to the reactivity of several substrates.

Domino carbometalation/coupling reactions of N-arylpropiolamides: a novel and promising synthetic strategy toward stereocontrolled preparation of highly substituted 3-methyleneindolinones

3-Methyleneindolinone derivatives are important structural motifs found in many compounds of natural occurrence and pharmacological significance.

Indium triflate catalysed 3-aza-Cope rearrangement of amino acid derived α,β-unsaturated esters to alkylidene oxindoles

The first examples of amino acid derived α,β-unsaturated esters to Z-alkylidene oxindoles via 3-aza-Cope rearrangement using In(OTf)₃ are reported.

Copper powder-catalyzed chelation-assisted cascade reaction of o-chloroarylacetic acids with amines under solvent- and ligand-free conditions: synthesis of oxindoles

Copper powder-catalyzed sequential C–Cl amination/intramolecular N-acylation under solvent- and ligand-free conditions is developed to access oxindoles.

Synthesis of Functionalized 6-Hydroxy-2-oxindole Derivatives by Phenoxide Cyclization

An apparent intramolecular cross-dehydrogenative coupling of N-(3-hydroxy)monoanilide of maleic esters comprising base promoted phenoxide cyclization and subsequent base-mediated aerobic oxidation was developed to synthesize a variety of 2-(6-hydroxy-2-oxoindolin-3-ylidene)acetate derivatives. The isolation of intermediate cyclized products during the large scale reactions and their ready dehydrogenation with 1 equiv of base support this proposed two-step path.

Highly stereoselective [4+2] and [3+2] spiroannulations of 2-(2-oxoindolin-3-ylidene)acetic esters catalyzed by bifunctional thioureas

A new Michael-Michael cascade reaction between 2-(2-oxoindolin-3-ylidene)acetic esters 1 and nitroenoates 2, catalyzed by bifunctional thioureas, is investigated. The combination of the two Michael reactions results in a novel and facile [4+2] or [3+2] spiroannulation process, which is characterized by the following features: 1) two carbon-carbon bonds and four stereocenters, including a quaternary spiro carbon, are formed under mild conditions; 2) an unprecedented and stereochemically defined substitution pattern on the spirocarbocyclic unit is obtained; 3) the double-bond configuration of the donor-acceptor nitroenoate 2 determines the absolute configuration of the spiro center, whereas the remaining stereocenters are formed under control of the catalyst. The effect on the final stereochemical outcome of structural variations of each starting material, catalyst, and experimental conditions is analyzed in detail. In particular, the use of specifically designed chiral nitroenoates enables diverse polyfunctional spirocyclohexane derivatives containing six consecutive stereogenic centers to be constructed. To our knowledge, this is the first asymmetric organocatalytic strategy enabling both five- and six-membered β-nitro spirocarbocyclic oxindoles.

Alkyne hydroarylation with Au N-heterocyclic carbene catalysts

Mono- and dinuclear gold complexes with N-heterocyclic carbene (NHC) ligands have been employed as catalysts in the intermolecular hydroarylation of alkynes with simple unfunctionalised arenes. Both mono- and dinuclear gold(III) complexes were able to catalyze the reaction; however, the best results were obtained with the mononuclear gold(I) complex IPrAuCl. This complex, activated with one equivalent of silver tetrafluoroborate, exhibited under acidic conditions at room temperature much higher catalytic activity and selectivity compared to more commonly employed palladium(II) catalysts. Moreover, the complex was active, albeit to a minor extent, even under neutral conditions, and exhibited lower activity but higher selectivity compared to the previously published complex AuCl(PPh(3)). Preliminary results on intramolecular hydroarylations using this catalytic system indicate, however, that alkyne hydration by traces of water may become a serious competing reaction.