Stereoselective Oxindole Synthesis by Palladium-Catalyzed Cyclization Reaction of 2-(Alkynyl)aryl Isocyanates with Amides

Ruthenium-catalyzed Heck coupling of 3-arylidene-oxindoles with alkenes: a facile synthesis of 3-allylidene-2(3H)-oxindoles

A simple and efficient Ru(II)-catalyzed olefination of 3-(arylbenzylidene)indolin-2-ones with alkenes is described. This is an atom and step-economical strategy with a wide substrate scope, good functional group tolerance, and suitability for gram scale synthesis. A plausible mechanism is also proposed for this synthetic transformation involving the formation of a 5-membered ruthenacycle and insertion of the alkene followed by β-hydride elimination to deliver the desired product.

Palladium-catalyzed amidation of carbazole derivatives via hydroamination of isocyanates

The first amidation of carbazoles at the N9 position via palladium-catalyzed hydroamination of isocyanates is demonstrated. This simple, general and efficient method could deliver a wide range of carbazole-N-carboxamides in up to 99% yield. The salient features of this transformation include simple conditions with no need for a strong base, high chemo- and regio-selectivities and good functional group tolerance. In particular, this work-up-free and chromatography-free protocol is time-saving, cost-effective and user-friendly.

Synthesis of Spiro[indoline-pyridine]-dicarboxylates and Substituted Alkylidene Oxindoles by Azomethine Ylides and MBH Carbonates of Isatins

We have developed an efficient protocol for the synthesis of spiro[indoline-pyridine]dicarboxylates and substituted alkylidene oxindoles through [3 + 3] cycloaddition and Michael addition individually by azomethine ylides and various MBH carbonates of isatins. The selective generation of cyclic products and chain products was achieved by changing the substituents at the 3-position of the oxindoles. The features of this method include convenient catalysts, mild reaction conditions, and broad substrate scopes.

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...

Cycloisomerization of Carbamoyl Chlorides in Hexafluoroisopropanol: Stereoselective Synthesis of Chlorinated Methylene Oxindoles and Quinolinones

Hexafluoroisopropanol (HFIP) was employed as an additive for the generation of 3-(chloromethylene)oxindoles via the chloroacylation of alkyne-tethered carbamoyl chlorides. This reaction avoids the use of a metal catalyst and accesses products in high yields and stereoselectivities. Additionally, this reaction is scalable and proved amenable to a series of product derivatizations, including the synthesis of nintedanib. The reactivity of alkene-tethered carbamoyl chlorides with hexafluoroisopropanol (HFIP) was harnessed towards the synthesis of 2-quinolinones.

Synthesis of (Z)-3-[amino(phenyl)methylidene]-1,3-dihydro-2H-indol-2-ones using an Eschenmoser coupling reaction

A highly modular method for the synthesis of (Z)-3-[amino(phenyl/methyl)methylidene]-1,3-dihydro-2H-indol-2-ones starting from easily available 3-bromooxindoles or (2-oxoindolin-3-yl)triflate and thioacetamides or thiobenzamides is described. A series of 49 compounds, several of which have previously been shown to possess significant tyrosin kinase inhibiting activity, was prepared in yields varying mostly from 70 to 97% and always surpassing those obtained by other published methods. The method includes an Eschenmoser coupling reaction, which is very feasible (even without using a thiophile except tertiary amides) and scalable. The (Z)-configuration of all products was confirmed by NMR techniques.

Stereoselective Formal Hydroamidation of Si-Substituted Arylacetylenes with DIBAL-H and Isocyanates: Synthesis of (E)- and (Z)-α-Silyl-α,β-unsaturated Amides

An efficient and stereoselective method for the synthesis of (E)- and (Z)-α-silyl-α,β-unsaturated amides and its synthetic applications are presented herein. The solvent-controlled hydroaluminations of Si-substituted alkynes with DIBAL-H generate diastereomerically enriched alkenylaluminum reagents that are directly reacted with isocyanates at ambient temperature to afford α-silyl-α,β-unsaturated amides in high yields with retained stereoselectivity. In particular, this process enables the synthesis of a broad range of (E)-α-silyl-α,β-unsaturated amides, which are the less studied isomers. The synthetic utility of this method is highlighted by its short reaction time, ease of purification, easily accessible substrates and reagents, gram-scale synthesis, and the further transformations of C-Si bonds into C-H, C-X, and C-C bonds.

Transition-Metal-Free Addition Reaction for the Synthesis of 3-(Aminobenzylidene/aminoalkylidene)indolin-2-ones and Its Synthetic Applications

A novel and efficient transition-metal-free approach for the exclusive synthesis of Z-3-(aminobenzylidene/aminoalkylidene)indolin-2-ones in high yield from 2-oxindole and aryl/alkyl nitrile in the presence of LiOtBu and 2,2'-bipyridine system is described. In addition, we disclosed a new approach towards the metal-free fluorination using selectfluor and the C═C bond cleavage using CuI and environmentally benign O₂.

Stereoselective Synthesis of Methylene Oxindoles via Palladium(II)-Catalyzed Intramolecular Cross-Coupling of Carbamoyl Chlorides

We report a highly robust, general and stereoselective method for the synthesis of 3-(chloromethylene)oxindoles from alkyne-tethered carbamoyl chlorides using PdCl₂(PhCN)₂ as the catalyst. The transformation involves a stereo- and regioselective chloropalladation of an internal alkyne to generate a nucleophilic vinyl Pd^II species, which then undergoes an intramolecular cross-coupling with a carbamoyl chloride. The reaction proceeds under mild conditions, is insensitive to the presence of moisture and air, and is readily scalable. The products obtained from this reaction are formed with >95:5 Z:E selectivity in nearly all cases and can be used to access biologically relevant oxindole cores. Through combined experimental and computational studies, we provide insight into stereo- and regioselectivity of the chloropalladation step, as well as the mechanism for the C-C bond forming process. Calculations provide support for a mechanism involving oxidative addition into the carbamoyl chloride bond to generate a high valent Pd^IV species, which then undergoes facile C-C reductive elimination to form the final product. Overall, the transformation constitutes a formal Pd^II-catalyzed intramolecular alkyne chlorocarbamoylation reaction.

Oxindole: A chemical prism carrying plethora of therapeutic benefits

Oxindole has emerged as a valuable scaffold in medicinal chemistry possessing diverse range of pharmacological activities. Its value has further been increased by its natural occurrence as alkaloids in variety of plants. It was first extracted from the cat claw's plant Uncaria tomentosa found in the Amazon rainforest and other tropical areas of South and Central America. Traditionally as well as present emerging therapeutic potential of oxindole nucleus has captured the interest of medicinal chemists to synthesize novel oxindole derivatives. In the present review the authors have integrated its chemistry and synthetic strategies developed after 1945. Also the information of naturally occurring oxindole alkaloids has been incorporated. The detailed pharmacological activities including anti-cancer, anti-HIV, antidiabetic, antibacterial, antioxidant, kinase inhibitory, AChE inhibitory, anti-leishmanial, β3 adrenergic receptor agonistic, phosphatase inhibitory, analgesic, spermicidal, vasopressin antagonists, progesterone antagonists, neuroprotection, and NMDA blocker activities of oxindole derivatives alongwith their SAR has also been discussed in detail. Additionally, information regarding the oxindole derivatives in clinical trials has been incorporated. Thus, this review will provide insights for the synthetic as well as medicinal chemist for the designing and synthesis of novel oxindole derivatives with novel improved range of pharmacological implications.

Controlling the ambiphilic nature of σ-arylpalladium intermediates in intramolecular cyclization reactions

The reactivity of main group organometallics, such as organolithium compounds (RLi) and Grignard reagents (RMgX), is quite straightforward. In these species the R group usually exhibits nucleophilic reactivity without any possibility of inducing electrophilic character. In contrast, in organopalladium complexes, researchers can switch the reactivity from electrophilic to nucleophilic relatively simply. Although σ-aryl and σ-vinylpalladium complexes are commonly used as electrophiles in C-C bond-forming reactions, recent research has demonstrated that they can also react with carbon-heteroatom multiple bonds in a nucleophilic manner. Nevertheless, researchers have completely ignored the issue of controlling the ambiphilic nature of such species. This Account describes our efforts toward selectively promoting the same starting materials toward either electrophilic α-arylation or nucleophilic addition reactions to different carbonyl groups. We could tune the properties of the σ-arylpalladium intermediates derived from amino-tethered aryl halides and carbonyl compounds to achieve chemoselective transformations. Therefore, chemists can control the ambiphilic nature of such intermediates and, consequently, the competition between the alternative reaction pathways by the adequate selection of the reaction conditions and additives (base, presence/absence of phenol, bidentate phosphines). The nature of the carbonyl group (aldehydes, ketones, esters, and amides) and the length of the tether connecting it to the aniline moiety also play an important role in the outcome of these processes. Our joint computational and experimental efforts to elucidate the reaction mechanism of these palladium-catalyzed transformations suggest that beyond the formation of the four-membered azapalladacycle, two major factors help to control the dual character of the palladium(II) intermediates derived from 2-haloanilines. First, their high nucleophilicity strongly modifies the interaction of the metal center with the carbonyl group. Second, the additive phenol exchanges the iodide ligand to give an arylpalladium(II) phenoxide complex, which has a beneficial effect on the arylation. The formation of this transient intermediate not only stabilizes the arylpalladium moiety, thus preventing the nucleophilic attack at the carbonyl group, but also assists the enolization reaction, which takes place in a more favorable intramolecular manner. The azapalladacycle intermediate is, in the words of J. R. R. Tolkien, "the one ring to bring them all and in the darkness to bind them." With this intermediate, we can easily achieve the synthesis of a variety of heterocyclic systems by selectively promoting electrophilic α-arylation or nucleophilic addition reactions from the same precursors.

Six-component reactions for the stereoselective synthesis of 3-arylidene-2-oxindoles via sequential one-pot Ugi/Heck carbocyclization/Sonogashira/nucleophilic addition

An efficient palladium-catalyzed protocol for the synthesis of 3-arylidene-2-oxindoles has been developed. In this approach, a sequential one-pot six-component reaction via Ugi/Heck carbocyclization/Sonogashira/nucleophilic addition was used for the synthesis of the desired skeleton.