De novo synthesis of benzofurans via trifluoroacetic acid catalyzed cyclization/oxidative aromatization cascade reaction of 2-hydroxy-1,4-diones

A facile, one-pot method for the de novo synthesis of benzofurans from 2-hydroxy-1,4-diones is described. Using trifluoroacetic acid (TFA) as the catalyst and N-bromobutanimide (NBS) as the oxidant, 2-hydroxy-1,4-diones underwent a cyclization/oxidative aromatization cascade reaction to afford a variety of benzofuran derivatives in moderate to good yields. This is a practically useful method for the synthesis of benzofuran derivatives starting from 2-hydroxy-1,4-diones which is also a supplement of the Paal–Knorr furan synthesis. A preliminary mechanism study was undertaken to support the proposed mechanism during which a novel 1,6-conjugate addition reaction was revealed.