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 de novo synthesis of benzofurans from 2-hydroxy-1,4-diones was described. Using trifluoroacetic acid (TFA) as the catalyst and N-bromobutanimide (NBS) as the oxidant, 2-hydroxy-1,4-diones underwent 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 that starting from 2-hydroxy-1,4-diones which is also a supplement of Paal-Knorr furan synthesis. Preliminary mechanism study was undertaken to support the proposed mechanism during which a novel 1,6-conjugate addition reaction was revealed.