Synthesis of spiro[2,3-dihydrofuran-3,3′-oxindole] derivatives via a multi-component cascade reaction of α-diazo esters, water, isatins and malononitrile/ethyl cyanoacetate

Abstract

We report a green synthesis of spiro[2,3-dihydrofuran-3,3′-oxindole] derivatives which are of potential value in medicinal chemistry. We are able to access spiro[2,3-dihydrofuran-3,3′-oxindole] derivatives via a Cu(OTf)₂-catalyzed or Cu(OTf)₂/Rh₂(OAc)₄-cocatalyzed multi-component cascade reaction of α-diazo esters, water, isatins and malononitrile/ethyl cyanoacetate. The reaction can be accomplished in good to excellent yields (60–99%), and the structure of products 6a and 6k was supported by X-ray crystallography. The catalyst Cu(OTf)₂ can be recycled 4 times without a sharp loss of the yield of 6a. 6q can be easily synthesized in gram scale. In brief, the reaction is characterized by step economy, a harmless solvent, and a recyclable catalyst.