Acid-catalyzed convenient transformation of 1-aryl-2-pentene-1,4-diones into polyfunctionalized furans

The reaction of phenylglyoxal with 2,4-pentanedione in the presence of boron trifluoride gave the unstable 3-acetyl-1-phenyl-2-pentene-1,4-dione intermediate which was converted in situ by the reaction with an excess amount of 2,4-pentanedione into new crystalline tri- and tetra-substituted furans. Other unstable 1-aryl-2-pentene-1,4-diones, which were obtained by the photooxygenation of 3-acetyl-5-aryl-2-methylfurans, were trapped by the acid-catalyzed reaction, giving polyfunctionalized furans in good yields. Treatment of the 1-phenyl-2-pentene-1,4-dione intermediate with concentrated hydrochloric acid followed by boiling ethanol quantitatively yielded a stable 2-ethoxymethylfuran via the unstable 2-chloromethylfuran.