Diastereoselective Construction of Spiro-furo[3,2-c]benzopyranoxindoles through a Cu(OTf)2/AcOH Cooperative Promoted Bicyclization Reaction

We disclose herein a highly diastereoselective approach for the Cu(OTf)2/AcOH cooperative promoted bicyclization reaction of 3-cinnamyl-3-hydroxy-2-oxindoles and ortho-quinonemethides (o-QMs) generated in situ from salicylaldehydes for the synthesis of spiro-furo[3,2-c]benzopyranoxindoles. The reaction has the advantages of readily available starting materials, simple operation, and high bond-forming efficiency, which not only provides an efficient access to spiro-furo[3,2-c]benzopyranoxindoles but also enriches the research contents of o-QMs-involved reactions. The synthetic applications of the products such as amide reduction are also demonstrated.