Copper-Mediated Construction of Spirocyclic Bis-oxindoles via a Double C–H, Ar–H Coupling Process

Recent Developments in Copper-Catalyzed Annulations for Synthesis of Spirooxindoles

Spirooxindoles represent a special scaffold for pharmaceuticals and natural products, and significant advancements have been achieved in their synthesis in recent years. Among these, transition metal catalysis, particularly copper catalysis, has emerged as an efficient and reliable method for the synthesis of spirooxindoles. Based on different reaction types, two distinct substrate types have been summarized and classified by us for constructing spirooxindole scaffolds via intramolecular and intermolecular annulations. This review outlines the latest advancements in copper-catalyzed cyclization reactions for synthesizing spirooxindoles and provides detailed insights into the types of annulation reactions and their possible reaction mechanisms.

Umpolung Strategy for the One-Pot Synthesis of Highly Steric Bispirooxindoles via the l-Amino Acid Ester-Promoted In Situ Reduction/Nucleophilic Addition/Cyclization Cascade Reaction

On the basis of a novel umpolung strategy, an efficient l-amino acid ester-mediated in situ reduction of 2-(2-oxoindolin-3-ylidene)malononitrile and sequential nucleophilic addition/cyclization cascade reaction is reported. Various densely substituted cyclopentene bispirooxindoles and dihydrofuran bispirooxindoles with two quaternary spirocenters were constructed in high yields (≤93%) with excellent diastereoselectivities (>20:1 dr). The method has advantages of readily available starting materials, mild reaction conditions, a one-pot process, a metal-free biomimetic reducing agent, a wide substrate scope, and operational simplicity (single filtration without column chromatography).

Palladium-Catalyzed Annulative Coupling of Spirovinylcyclopropyl Oxindoles with p-Quinone Methides

Pd-catalyzed annulative coupling of spirovinylcyclopropyl oxindoles with p-quinone methides has been accomplished via cascade carbon-carbon bond formation to afford bis-spirooxindole scaffolds. The mild reaction conditions, diastereoselectivity, functional group diversity, post-synthetic transformations, and mechanistic studies using DFT calculations are the important practical features.

Access to densely functionalized spirocyclopentenonyl oxindole frameworks via aza- and carbo-Piancatelli rearrangement

A new strategy for access to spirocyclopentenonyl oxindole frameworks is disclosed. Suitably anchored furfuryl alcohol at C3 of an oxindole was used for the aza-Piancatelli rearrangement, which furnished spirocyclic aminocyclopentenone frameworks with catalytic phosphomolybdic acid. The scope of the transformation was extended to the carbo-Piancatelli rearrangement with various indole derivatives.

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.

Cross-Dehydrogenative Cyclization-Dimerization Cascade Sequence for the Synthesis of Symmetrical 3,3'-Bisoxindoles

The synthesis of symmetrical 3,3'-bisoxindoles from simple acyclic β-oxoanilides is reported. The described method forges three new C-C bonds in a single step via a sequential Mn(OAc)₃·2H₂O mediated oxidative radical cyclization-fragmentation-dimerization process. The scope of this reaction is demonstrated in the preparation of a variety of 3,3'-bisoxindoles, as well as its application toward the formal synthesis of the Calycanthaceae alkaloid, (±)-folicanthine.

Stereoselective synthesis and applications of spirocyclic oxindoles

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

Umpolung Strategy for the Synthesis of Chiral Dispiro[2-amino-4,5-dihydrofuran-3-carbonitrile]bisoxindoles

Based on a novel umpolung strategy, an efficient and highly enantioselective cascade aldol/cyclization/tautomerization of the 2-(2-oxoindolin-3-yl)malononitrile to active carbonyl compounds with excellent diastereo- and enantioselectivity has been developed. Also, various enantio-enriched multifunctional dispiro[2-amino-4,5-dihydrofuran-3-carbonitrile]bisoxindoles with adjacent spiro-stereocenters were conveniently obtained by this novel methodology. Also, the dispiro[2-amino-4,5-dihydrofuran-3-carbonitrile]bisoxindoles were easily transformed into structurally complex molecules without any effect on the diastereo- and enantioselectivity.

Lewis acid catalyzed annulation of spirocyclic donor–acceptor cyclopropanes with exo-heterocyclic olefins: access to highly functionalized bis-spirocyclopentane oxindole frameworks

Oxindole-activated spiro-DAC is used as synthon to prepare complex bis-spirocyclopentane oxindole frameworks via ring-enlargement.

3d Transition Metals for C-H Activation

C-H activation has surfaced as an increasingly powerful tool for molecular sciences, with notable applications to material sciences, crop protection, drug discovery, and pharmaceutical industries, among others. Despite major advances, the vast majority of these C-H functionalizations required precious 4d or 5d transition metal catalysts. Given the cost-effective and sustainable nature of earth-abundant first row transition metals, the development of less toxic, inexpensive 3d metal catalysts for C-H activation has gained considerable recent momentum as a significantly more environmentally-benign and economically-attractive alternative. Herein, we provide a comprehensive overview on first row transition metal catalysts for C-H activation until summer 2018.

Low-Temperature, Transition-Metal-Free Cross-Dehydrogenative Coupling Protocol for the Synthesis of 3,3-Disubstituted Oxindoles

A new low-temperature procedure for the synthesis of 3,3-disubstituted 2-oxindoles via cross-dehydrogenative coupling (CDC) is reported. The use of a strong, nonreversible base in these reactions has been found to effect a dramatic drop in reaction temperature (to room temperature) relative to the current state-of-the-art (>100 °C) procedure. When employing iodine as an "oxidant", new evidence suggests that this transformation may occur via a transiently stable iodinated intermediate rather than by direct single-electron oxidation.

Photoredox-catalyzed procedure for carbamoyl radical generation: 3,4-dihydroquinolin-2-one and quinolin-2-one synthesis

A reductive approach for carbamoyl radical generation from N-hydroxyphthalimido oxamides under photoredox catalysis is outlined. This strategy was applied to the synthesis of 3,4-dihydroquinolin-2-ones via the intermolecular addition/cyclization of carbamoyl radicals with electron deficient olefins in a mild, redox-neutral manner. Under a general set of reaction conditions, diversely substituted 3,4-dihydroquinolin-2-ones, including spirocyclic systems can be prepared. By using chlorine-substituted olefins, aromatic quinolin-2-ones can also be accessed.

Cyclodimerization of 3-phenacylideneoxindolines with amino esters for the synthesis of dispiro[indoline-3,1′-cyclopentane-3′,3″-indolines]

Triethylamine-promoted domino cyclodimerization reaction of 3-phenacylideneoxindolines with amino ester hydrochlorides in acetonitrile afforded substituted dispiro[indoline-3,1′-cyclopentane-3′,3″-indolines] in good yields. The relative configuration of the major diastereoisomers was determined by the X-ray diffraction analysis of three single crystal structures.

Diastereoselective synthesis of dispiro[indoline-3,1′-cyclobutane-2′,3″-indolines] via visible light catalyzed cyclodimerization of 3-phenacylideneoxindoles

A simple synthetic protocol was developed for the efficient synthesis of functionalized dispiro[indoline-3,1′-cyclobutane-2′,3″-indolines] with high diastereoselectivity. The reaction proceeds by cyclodimerization reaction of 3-phenacylideneoxindoles in the presence of a catalytic amount of photosensitizer Ru(bpy

Mg(ClO4)2-promoted [4 + 3] cycloaddition of oxindole derivatives with conjugated dienes: concise synthesis of spirocycloheptane oxindole derivatives

Novel Mg(ClO₄)₂-promoted [4 + 3] cycloaddition reaction of oxindole derivatives and cyclopentadiene was achieved for the construction of the spirocycloheptane oxindole skeleton.

[4 + 3] Cycloadditions with Bromo-Substituted Morita-Baylis-Hillman Adducts of Isatins and N-(ortho-Chloromethyl)aryl Amides

Efficient construction of a challenging aza-spirocycloheptane oxindole scaffold is reported through an unprecedented [4 + 3] cycloaddition reaction with bromo-substituted Morita-Baylis-Hillman adducts of isatins and N-(ortho-chloromethyl)aryl amides. Both reactive intermediates, the allylic phosphonium ylides and aza-o-quinone methides, were in situ generated, chemoselectively facilitated by a Lewis base and Brønsted base, respectively.

Highly diastereoselective synthesis of imidazolidine-dispirooxindoles via three-component [3 + 2] cycloadditions of isatins, 2-(aminomethyl)pyridine and isatin-based imines

In the presence of Et₃N, the [3 + 2] cycloaddition of isatins, 2-(aminomethyl)pyridine and isatin-based imines proceeded readily, and furnished novel imidazolidine-dispirooxindoles in up to 84% yield with up to >99 : 1 diastereoselectivity.

Di-tert-butyl peroxide (DTBP) promoted dehydrogenative coupling: an expedient and metal-free synthesis of oxindoles via intramolecular C(sp2)–H and C(sp3)–H bond activation

An efficient di-tert-butyl peroxide (DTBP) promoted synthesis of oxindole has been developed. This methodology involves C(sp³)–H and C(sp²)–H bond activation under metal-free conditions.