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A general and practical three-component regioselective 1,3-dipolar cycloaddition of 3-amino-oxindole-based azomethine ylides and coumarins has been developed. This reaction displayed good substrate tolerance and gave a diverse array of biologically relevant spiro[ox--i-ndole-pyrrolidine-dihydrocoumarin] derivatives bearing four contiguous stereocenters including one spiro quaternary center in moderate to high yields (up to 90%) with high diastereoselectivities (up to 15:1 dr). It is based on the application of carboxylic acid activated coumarins as dienophiles followed by a decarboxylation process. The possible mechanism of the 1,3-dipolar cycloaddition is proposed via an exo ′-transition state. Furthermore, this is the first example of decarboxylative-mediated regioselective 1,3-dipolar cycloaddition of 3-amino-oxindole-based azomethine ylides and coumarins. [ABSTRACT FROM AUTHOR]

A thiourea-catalyzed asymmetric domino Michael/annulation process was devised employing bifunctional oxindole-chromones as C4 synthons and β,γ-unsaturated α-keto esters as C2 synthons. This reaction enables the highly diastereo- and enantioselective synthesis of a range of biologically relevant spirocyclic hexahydroxanthones with one quaternary and four tertiary stereogenic centers, also featuring an intriguing combination of two privileged motifs, including hexahydroxanthone and oxindole substructures, in good yields (up to 76%) and excellent stereoselectivities (up to >99% ee and >20:1 dr). Moreover, using β,γ-unsaturated α-keto esters as the C2 building blocks, which are different from enone substrates such as chalcone and benzalacetone, with the reversible Michael reaction further expanded the scope of the method. In addition, scale-up also demonstrated the applicability of this protocol. [ABSTRACT FROM AUTHOR]

The direct use of ammonium hydroxide in amination for the synthesis of primary amines is considered to be one of the major challenges in synthetic organic chemistry. Herein, the first example of catalyst-free direct amination of 3-halooxindoles with ammonium hydroxide to synthesize N-unprotected 3-tetrasubstituted aminooxindoles in high yields (up to 91% yield) is described. An enhancement of the reaction rate on using water was observed under mild conditions. Such an approach is not only protection/deprotection-free, but also more practical and cost-effective. Moreover, this method could expand the library of 3-tetrasubstituted aminooxindole building blocks for the further synthesis of AG-041R, GHSR antagonists and a charteline unit, opening up a new synthetic pathway in the chemistry of 3-aminooxindoles. [ABSTRACT FROM AUTHOR]

A new method was developed for the facile one-pot multicomponent construction of heterocycle-fused spiro compounds containing chromanone and pyrrolidinyl spirooxindoles, two potential pharmacophores, in one molecule through a decarboxylative 1,3-dipolar [3 + 2] cycloaddition reaction of carboxylic acid group-activated chromones 1 with isatin-derivated azomethine ylides based on molecular hybridization strategy. A wide variety of products with three contiguous stereocenters including a spiro quaternary stereocenter were smoothly prepared with high efficiency (up to 87% yield and 20:1 diastereomeric ratio). This method could offer libraries of architecturally diverse and multiple pharmacore collections, potentially useful in medicinal chemistry. [ABSTRACT FROM AUTHOR]