Spirooxindoles from a 3-CR of Imines, Diazoesters, and Olefin Dipolarophiles

Significance

A three-component reaction for the construction of spiropyrrolidinyloxindoles is reported. The reaction proceeds by initial CuOTf-catalyzed α-diazoester-imine coupling to form an azomethine ylide which undergoes subsequent highly diastereoselective cycloaddition with the oxindole dipolarophile to afford the products. An X-ray crystallographic structure analysis established the relative configuration of a selected product. The authors propose an E-exo [2+3] transition state for the cycloaddition reaction because the dipolarophile alkene geometry is directly translated into the product with exo-face selectivity. This diastereoselectivity also suggests that cyclo­addition is faster than in situ azomethine ylide E-to-Z isomerization (C. V. Galliford, M. A. Beenen, S. T. Nguyen, K. A. Scheidt Org. Lett. 2003, 5, 347-3490).