Enantioselective Synthesis of Spirooxindole-Pyran and Furan Scaffolds via Copper-Catalyzed Formal (3+3) and (3+2) Cycloaddition of Isatin-Derived Propargylic Esters

Abstract

Herein, we report a copper-catalyzed enantioselective formal (3+3) and (3+2) cycloaddition reaction of isatin-derived tertiary propargylic esters with N,N-dimethylbarbituric acid and 4-hydroxycoumarins, respectively. In this process, the tertiary propargylic ester serves as both C3- and C2-synthons, facilitating the synthesis of optically active spirooxindole-pyran and furan scaffolds featuring an all-carbon quaternary stereocenter. The reaction delivers these spirocyclic frameworks in good yields with high enantioselectivities. Additionally, the scalability of both the reactions and the transformation of chiral intermediates into valuable structures emphasize the synthetic and practical importance of this strategy.

Keywords: All-carbon quaternary stereocenter; Catalytic asymmetric propargylic cycloaddition; Spirooxindole-furans; Spirooxindole-pyrans.