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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]