Synthesis of spiro[2,3-dihydrofuran-3,3′-oxindole] via a multi-component cascade reaction of α-diazo esters, water, isatins and malononitrile/ethyl cyanoacetate
We reported a green synthesis of spiro[2,3-dihydrofuran-3,3′-oxindole] derivatives which are of potential value in medicinal chemistry. We are able to accesses to 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 ester, water and isatins and malononitrile/cyanoacetate. The reaction could be accomplished in good to excellent yields (60-99%) and the structure of products 6a and 6k were unambiguously confirmed by X-ray crystallography. The catalyst Cu(OTf)2 could be recycled for 4 times without a sharp loss of the yield of the product 6a. 6p could be synthesized from glycine methyl ester hydrochloride, isatin, and malononitrile with a safe and gram-scale procedure where methyl diazoacetate and isatylidene malononitrile were generated in situ. Overall, the reaction characterized with step-economy, harmless solvent, and recyclable catalyst represents a good example in green chemistry.