Self [3 + 4] Cycloadditions of Isatin N,N′-Cyclic Azomethine Imine 1,3-Dipole with N-(o-Chloromethyl)aryl Amides

Synthesis of benzimidazole-fused 1,4-benzoxazepines and benzosultams spiro-connected to a 2-oxindole core via a tandem epoxide-opening/SNAr approach

While hundreds of literature reports describe the preparation of spirooxindole-based five- and six-membered heterocycles, the construction of seven-membered heterocyclic rings spiro-connected to a 2-oxindole core has so far been less developed. Herein, we disclose a base-mediated (4 + 3) annulation of spiro-epoxyoxindoles and 2-(2-fluoroaryl)-1H-benzoimidazoles or 2-fluoro-N-arylbenzenesulfonamides toward the synthesis of two new classes of spirooxindole-based polycyclic systems. Mechanistically, this conceptually simple and high atom-economical reaction proceeds via an SN2-like intermolecular epoxide ring-opening, accompanied by a concomitant intramolecular SNAr reaction. From a synthetic aspect, the notable features of the process are its full regioselectivity, operational simplicity using readily available substrates under transition-metal-free conditions, high yields, and broad substrate scope.

DABCO-Catalyzed Mono-/Diallylation of N-Unsubstituted Isatin N,N′-Cyclic Azomethine Imine 1,3-Dipoles with Morita-Baylis-Hillman Carbonates

Allylation of N-unsubstituted isatin N,N′-cyclic azomethine imines with Morita-Baylis-Hillman carbonates in the presence of 1–10 mol% DABCO in DCM at room temperature, rapidly gave N-allylated and N, β-diallylated isatin N,N′-cyclic azomethine imine 1,3-dipoles in moderate to high yields. The reaction features mild reaction conditions, easily practical operation, and short reaction times in most cases. Furthermore, the alkylated products were transformed into novel bicyclic spiropyrrolidine oxoindole derivatives through the [3+2] or [3+3]-cycloaddition with maleimides or Knoevenagel adducts.

K2CO3-Promoted Formal [3+3]-Cycloaddition of N-Unsubstituted Isatin N,N'-Cyclic Azomethine Imine 1,3-Dipoles with Knoevenagel Adducts

The synthesis of dicyclic spiropyridazine oxoindole derivatives by using [3+3]-cycloaddition of N-unsubstituted isatin N,N'-cyclic azomethine imine 1,3-dipoles was reported. The products bearing two consecutive stereocenters, including spiroquaternary stereocenters in one ring structure, can be effectively obtained in moderate to excellent yields (20-93%) and low to moderate diastereoselectivities (1:9-10:1 dr). The synthesized compounds (>35 examples) were characterized by single-crystal XRD, FTIR, NMR, and mass spectral analysis.

Construction of pyrazolodiazepines using AuI, a dual functional gold catalyst

N,N'-5,7-Fused compounds are important molecules exhibiting medicinal potential. Herein, we report a practical and robust method for synthesising pyrazolodiazepines from N-piperidinyl alkynylhydrazides using a AuI catalyst. The broad substrate scope of alkynylhydrazides and synthetic application of pyrazolodiazepines are demonstrated. In addition, control experiments provide detailed information on the reaction mechanism, in which AuI promotes both the sequential intramolecular nucleophilic addition and the double nucleophilic substitution reaction as a π-acidic and nucleophilic dual functional catalyst.

[4+n] Annulation Reactions Using ortho-Chloromethyl Anilines as Aza-ortho-Quinone Methide Precursors

Aza-ortho-quinone methides are important reactive intermediates that have found broad applications in synthetic chemistry. Recently, 1,4-elimination of ortho-chloromethyl aniline derivatives has emerged as a novel, powerful and convenient method for aza-ortho-quinone methide generation. This review will highlight the recent applications of aza-ortho-quinone methide precursors in annulation reactions to access various biologically important nitrogen-containing heterocycles. The general mechanisms are briefly discussed as well.

1 Introduction

2 [4+n] Annulation Reactions Using ortho-Chloromethyl Anilines as Aza-ortho-Quinone Methide Precursors

2.1 [4+2] Annulation Reactions

2.2 [4+1] Annulation Reactions

2.3 [4+3] Annulation Reactions

3 Conclusion and Perspective

Catalytic Asymmetric Construction of a 1,2,4-Benzotriazepine Skeleton via Diastereo- and Enantioselective Decarboxylative [4 + 3] Cyclization

We have developed a protocol for palladium-catalyzed decarboxylative [4 + 3] cycloaddition reactions between 4-vinyl benzoxazinanones and azomethine imines to generate moderate to good yields of structurally diverse 1,2,4-benzotriazepines bearing two stereogenic centers with good to excellent stereoselectivities. This protocol not only addresses the challenge of asymmetrically constructing compounds with a 1,2,4-benzotriazepine skeleton but also demonstrates the utility of decarboxylative cycloadditions for the synthesis of enantioenriched polycyclic compounds.

(4 + 2) cyclization of aza-o-quinone methides with azlactones: construction of biologically important dihydroquinolinone frameworks

A base-promoted (4 + 2) cyclization of aza-o-quinone methides (aza-o-QMs) in situ generated from N-(o-chloromethyl)aryl amides was established. In this approach, azlactones were utilized as competent two-atom reaction partners to undergo (4 + 2) cyclization with aza-o-QMs, which afforded a series of dihydroquinolinone derivatives in overall good yields (up to 98%). This protocol has not only advanced the development of aza-o-QM-involved reactions, but also offered a useful method for constructing biologically important dihydroquinolinone frameworks.

Rapid umpolung Michael addition of isatin N,N′-cyclic azomethine imine 1,3-dipoles with chalcones

3,3-Disubstituted oxindoles were prepared rapidly in moderate to excellent yields with promising dr values by the t-BuONa-promoted Michael addition.

An overview of the reactions involving azomethine imines over half a decade

Azomethine imines constitute a versatile class of 1,3-dipoles which was used extensively for biologically relevant N-heterocycle synthesis – a five-year recap.

Recent advances in organocatalytic asymmetric multicomponent cascade reactions for enantioselective synthesis of spirooxindoles

Catalytic asymmetric MCCRs for enantioselective synthesis of spirooxindoles by using chiral phosphoric acids, amines, bifunctional thiourea/squaramides and metal-based reagents as catalysts.

A Role for Isatin Azomethine Imines as a Dipolarophile in Cycloaddition Reactions

An unusual [2 + 3] cycloaddition of isatin azomethine imines (AIs) and in situ generated azaoxyallyl cations has been developed. It is the first example where AIs serve as the [C,O] 2-atom synthon in organic synthesis. This work not only reveals a new role of isatin AIs in cycloaddition reaction but also provides an efficient access to unprecedented spiroheterocycle compounds.

1,3-Dipolar cycloaddition of isatin N,N'-cyclic azomethine imines with α,β-unsaturated aldehydes catalyzed by DBU in water

A simple and green procedure was established by [3 + 3] cycloaddition reaction of isatin derived cyclic imine 1,3-dipoles with α,β-unsaturated aldehydes, giving the desired spiro heterocyclic oxindoles with aza-quaternary centers in good yields and diastereoselectivities. It should be noted that water can be employed as a suitable solvent for the improvement of diastereoselectivity.

A simple and green procedure was established by [3 + 3] cycloaddition reaction of isatin derived cyclic imine 1,3-dipoles with α,β-unsaturated aldehydes, giving spirooxindoles with aza-quaternary center in good yields and diastereoselectivities.

A [3 + 2] cycloaddition/C-arylation of isatin N,N′-cyclic azomethine imine 1,3-dipole with arynes

A [3 + 2] annulation/C-arylation reaction of 1,3-dipole 1 with arynes has been established for the synthesis of oxindole scaffolds.

Diverse reactivity of isatin-based N,N′-cyclic azomethine imine dipoles with arynes: synthesis of 1′-methyl-2′-oxospiro [indene-1,3′-indolines] and 3-aryl-3-pyrazol-2-oxindoles

Reaction of aryne with isatin based N,N′-cyclic AMI 1,3-dipole afforded 3,3-disubstituted oxindole while methyl substitution on the pyrrolidine ring of 1,3-dipole directed [3+2] cycloaddition products.

Rapid abnormal [3+2]-cycloaddition of isatin N,N′-cyclic azomethine imine 1,3-dipoles with chalcones

More than 35 new compounds were prepared rapidly in moderate to excellent yields with high diastereoselectivities by K₂CO₃-promoted abnormal 1,3-diploar cycloaddition of isatin N, N′-cyclic azomethine imines with chalcones.

Efficient and environmentally sustainable domino protocol for the synthesis of diversified spiroheterocycles with privileged heterocyclic substructures using bio-organic catalyst in aqueous medium

An efficient and environmentally sustainable synthetic protocol has been presented to synthesize structurally diverse spiroxindoles spiroannulated with indenopyrroloimidazoles, pyranopyrroloimidazoles, chromenopyrroloimidazoles, and imidazopyrrolopyrimidines involving three-component reaction of isatins, hydantoin, and β-diketones in the presence of green and sustainable bio-organic catalyst, β-amino acid, 2-aminoethanesulfonic acid (taurine), in aqueous media. The synthetic efficiency, operational simplicity, and reusability of catalyst make the present synthetic protocol cost effective, time efficient, and eco-friendly to synthesize molecules with structural diversity and molecular complexity and expected to contribute significantly not only to drug discovery research but also to pharmaceutical and medicinal chemistry.

Diastereoselective construction of a functionalized dihydro-pyridazine-based spirooxindole scaffold via C-3 umpolung of isatin N,N′-cyclic azomethine imine

This study demonstrates an abnormal [3+3] tandem Michael addition/N-cyclization of isatin N,N′-cyclic azomethine imine 1,3-dipoles and 2-arylidene malononitrile that diastereoselectively construct a dihydro-pyridazine-based spirooxindole.

Synthesis of spirooxindoles fused with pyrazolo-tetrahydropyridinone and coumarin-dihydropyridine-pyrazole tetracycles by reaction medium dependent isatin-based multicomponent reactions

A reaction medium dependent three-component reaction of isatin, 4-hydroxycoumarin and aminopyrazole/aminoisoxazole has been reported under microwave heating conditions for the synthesis of two different types of fused spirooxindoles.

Synthesis of Spiro[oxindole-3,2'-pyrrolidine] Derivatives from Benzynes and Azomethine Ylides through 1,3-Dipolar Cycloaddition Reactions

A novel synthetic strategy employing benzyne and azomethine ylides for the construction of spiro[oxindole-3,2'-pyrrolidine] derivatives has been achieved in good yields. The ketimines obtained from the condensation of isatins with CF₃CH₂NH₂ react with benzyne in the presence of weak bases such as TBAF or TBAT. This mild practical 1,3-dipolar cycloaddition provides an efficient route to access biologically active compounds.

Base-mediated [2 + 4] cycloadditions of in situ formed azaoxyallyl cations with N-(2-chloromethyl)aryl amides

A base-mediated [2 + 4] annulation of in situ formed azaoxyallyl cations with in situ generated aza-oQMs has been realized.