Asymmetric Synthesis of Spiro-3,3'-cyclopropyl Oxindoles via Vinylogous Michael Initiated Ring Closure Reaction

A novel organocatalytic cascade approach for the synthesis of spiro-cyclopropyl oxindole derivatives has been developed. The methodology is based on asymmetric vinylogous Michael addition of 4-nitroisoxazole derivatives to N-Boc isatylidene malonates followed by intramolecular alkylation. Its remarkable stereocontrol, wide substrate scope, and scalability highlight this new developed strategy. Moreover, this work represents the first example of vinylogous Michael initiated ring closure (MIRC) reaction for the synthesis of chiral 3,3'-cyclopropyl oxindole.

Tandem 1,6-addition/cyclopropanation/rearrangement reaction of vinylogous para-quinone methides with 3-chlorooxindoles: construction of vicinal quaternary carbon centers

A novel tandem 1,6-addition/cyclopropanation/rearrangement reaction of vinylogous para-quinone methides with 3-chlorooxindoles has been developed, providing dispirooxindole–cyclopentane–cyclohexadienones with vicinal quaternary carbon centers.

Synthesis of functionalized 3,2′-pyrrolidinyl spirooxindoles via domino 1,6-addition/annulation reactions of para-quinone methides and 3-chlorooxindoles

A highly efficient diastereoselective [4 + 1] cycloaddition of ortho-tosylaminophenyl-substituted p-QMs with 3-chlorooxindoles has been developed to afford 3,2′-pyrrolidinyl spirooxindoles.

A novel methodology for the efficient synthesis of 3-monohalooxindoles by acidolysis of 3-phosphate-substituted oxindoles with haloid acids

A novel method for the synthesis of 3-monohalooxindoles by acidolysis of isatin-derived 3-phosphate-substituted oxindoles with haloid acids was developed. This synthetic strategy involved the preparation of 3-phosphate-substituted oxindole intermediates and S_N1 reactions with haloid acids. This new procedure features mild reaction conditions, simple operation, good yield, readily available and inexpensive starting materials, and gram-scalability.

Regiodivergent Organocatalytic Reactions

Organocatalysts are abundantly used for various transformations, particularly to obtain highly enantio- and diastereomeric pure products by controlling the stereochemistry. These applications of organocatalysts have been the topic of several reviews. Organocatalysts have emerged as one of the very essential areas of research due to their mild reaction conditions, cost-effective nature, non-toxicity, and environmentally benign approach that obviates the need for transition metal catalysts and other toxic reagents. Various types of organocatalysts including amine catalysts, Brønsted acids, and Lewis bases such as N-heterocyclic carbene (NHC) catalysts, cinchona alkaloids, 4-dimethylaminopyridine (DMAP), and hydrogen bond-donating catalysts, have gained renewed interest because of their regioselectivity. In this review, we present recent advances in regiodivergent reactions that are governed by organocatalysts. Additionally, we briefly discuss the reaction pathways of achieving regiodivergent products by changes in conditions such as solvents, additives, or the temperature.

A formal intermolecular [4 + 1] cycloaddition reaction of 3-chlorooxindole and o-quinone methides: a facile synthesis of spirocyclic oxindole scaffolds

Herein, we developed an efficient and straightforward method for the rapid synthesis of spirocyclic oxindole scaffolds via the [4 + 1] cyclization reaction of 3-chlorooxindole with o-quinone methides (o-QMs), which were generated under mild conditions. The products could be obtained in excellent yields with numerous types of 3-chlorooxindole. This methodology features mild reaction conditions, high atom-economy and broad substrate scope.

Herein, we developed an efficient and straightforward method for the rapid synthesis of spirocyclic oxindole scaffolds via the [4 + 1] cyclization reaction of 3-chlorooxindole with o-quinone methides (o-QMs), which were generated under mild conditions.

Organocatalytic Asymmetric Cyclopropanation of 3-Acylcoumarins with 3-Halooxindoles: Access to Spirooxindole-cyclopropa[c]coumarin Compounds

A highly diastereo- and enantioselective cyclopropanation reaction of 3-acylcoumarins with 3-halooxindoles catalyzed by an organocatalyst through a [2 + 1] Michael/intramolecular cyclization process was developed. This scenario provides a facile strategy to access spirooxindole-cyclopropa[c]coumarin compounds bearing three continuous stereocenters, including two vicinal quaternary all-carbon stereocenters with high to excellent diastereo- and enantioselectivities. The HRMS study revealed the vital importance of the ammonium ylide intermediate in the catalytic process.

Stereoselective synthesis and applications of spirocyclic oxindoles

This review summaries recent synthetic developments towards spirocyclic oxindoles and applications as valuable medicinal and synthetic targets.

Synthesis of Spiro 3,3'-Cyclopropyl Oxindoles Via N-Bromosuccinimide-Mediated Ring-Closing and Contraction Cascade

An N-bromosuccinimide-mediated cascade reaction involving the cyclization/oxygen-migration/ring-contraction process of 3-(β, β-diaryl) indolylethanol was disclosed. A variety of spiro 3,3'-cyclopropyl oxindole derivatives were efficiently synthesized in good yields under mild reaction conditions. A possible mechanism was suggested based on intermediate isolation and computational studies.