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Synthesis of Furans via Copper-Catalyzed [4+1] Cycloaddition
L.-B. Zhao, Z.-H. Guan, Y. Han, Y.-X. Xie, S. He, Y.-M. Liang*
Lanzhou University, P. R. of China
21 February 2008 (online)
A copper-catalyzed [4+1] cycloaddition of α,β-acetylenic ketones with diazoacetates to produce 2,3,5-trisubstituted furans in moderate to good yield is reported. Cu(II) salts [e.g., CuSO4, CuOTf, Cu(acac)2] were found to be ineffective for the cyclization; among other Cu(I) salts, CuI was found to be the best catalyst in dichloroethane. Attempts to replace diazoacetates with other diazo compounds [e.g., CH2N2, TMS/diazomethane, PhCHN2, 1-(α-diazoglycyl)piperidine] under these reaction conditions failed to give any desired product.