Direct synthesis of N-functionalized indoles through isomerization of azomethine ylides

An unexpected isomerization of azomethine ylides generated in situ from isatin with indoline-2-carboxylic acid has been disclosed, providing direct access to N-functionalized indole scaffolds. This protocol has good functional group tolerance and provides various 3-(1H-indol-1-yl)indolin-2-one derivatives in moderate to high yields simply by using alcohol as the solvent, with no additional additive being required.

Dipolarophile-Controlled Regioselective 1,3-Dipolar Cycloaddition: A Switchable Divergent Access to Functionalized N-Fused Pyrrolidinyl Spirooxindoles

N-fused pyrrolidinyl spirooxindole belongs to a class of privileged heterocyclic scaffolds and is prevalent in natural alkaloids and synthetic pharmaceutical molecules. To realize the switchable synthesis of divergent N-fused pyrrolidinyl spirooxindoles for further biological activity evaluation via a substrate-controlled strategy, a chemically sustainable, catalysis-free, and dipolarophile-controlled three-component 1,3-dipolar cycloaddition of isatin-derived azomethine ylides with diverse dipolarophiles is described in this work. A total of 40 functionalized N-fused pyrrolidinyl spirooxindoles were synthesized in 76-95% yields with excellent diastereoselectivities (up to >99:1 dr). The scaffolds of these products can be well-controlled by employing different 1,4-enedione derivatives as dipolarophiles in EtOH at room temperature. This study provides an efficient strategy to afford a spectrum of natural-like and potentially bioactive N-fused pyrrolidinyl spirooxindoles.

A three-component [3 + 2]-cycloaddition/elimination cascade for the synthesis of spirooxindole-pyrrolizines

A three-component synthesis of novel spirooxindole-tetrahydropyrrolizines from secondary α-aminoacids, isatins and vinyl selenones has been disclosed. Products were formed in good yields and high diastereoselectivity by 1,3-dipolar cycloaddition of in situ generated azomethine ylides followed by spontaneous elimination of benzeneseleninic acid. Good regioselectivities with aryl substituted vinyl selenones were observed. The method showed good functional group tolerance, providing a direct approach to biologically relevant spirooxindoles under mild reaction conditions.

Enantioselective organocatalytic formal [3+2]-cycloaddition of isatin-derived ketimines with benzylidenemalononitriles and benzylidineindanones

Electron-deficient alkenes undergo organocatalysed formal [3+2]-cycloaddition with isatin-derived imines, generating complex spirocyclic products with high yield and stereoselectivity.

Dehydrative Transformation of Spirooxindoles to Pyrido[2,3-b]indoles via POCl3

A two-step one-pot efficient synthesis of pyrido[2,3-b]indoles via reaction between isatin, α-amino acid, and dipolarophile has been developed. The initial 1,3-dipolar cycloaddition between the reactants that is performed in the presence of either CuI or methanol results in spirooxindoles that undergo POCl₃-mediated intramolecular dehydrative transformation to afford the title compounds.

Pseudo five component reaction towards densely functionalized spiro[indole-3,2'-pyrrole] by picric acid, an efficient syn-diastereoselective catalyst: insight into the diastereoselection on C(sp3)-C(sp3) axial conformation

A new series of highly-functionalized spiro compounds of pyrrole were synthesized by a one pot, step-economic condensation of isatin, arylamine and β-keto ester catalyzed by wet picric acid. Initially, the reaction was proposed with an expectation of the formation of a multi-spiro heterocyclic framework of highly-substituted piperidine. However, the isomeric compound was characterized to be a five-membered pyrrole derivative with a diverse scope of variations having different types of substituents in the three components respectively. The possibility of formation of various diastereomers around the hindered single bond and the spiro carbon was limited, as only syn products syn-60 and syn-60' were isolated in all the reactions performed under the standard conditions. Probably the reactions were mediated by the si-facial formation of the bonds in a picric acid stabilized charge transfer complex transition state. Also, the manner a molecule achieves the most stabilized energy minimized arrangement with all its substituents in space was studied by DFT calculations where syn-60 was more stable than syn-60'. The studies on the formation of syn-60 and syn-60' were carried out by variation of electronic and steric factors in each of the components of the reactions.

A Critical Review on Advances in the Multicomponent Synthesis of Pyrroles

Nitrogen containing heterocyclic compounds are biologically significant molecules. This is especially true for pyrrole a five membered nitrogen containing aromatic molecule, which is present as a key structural motif in a large number of drugs and lead molecules. This review aims to provide an overview of the multi-component reaction (MCR) based methodologies used for the synthesis of pyrrole and its derivatives, focusing particularly on eco-friendly methods that avoid the use of hazardous reagents, solvents and catalysts are deemed especially relevant to the disciplines of medicinal chemistry and drug discovery.