Stereoselective Synthesis of cis-2-Ene-1,4-diones via Aerobic Oxidation of Substituted Furans Catalyzed by ABNO/HNO3.

We report a highly efficient and selective catalytic system, ABNO (9-azabicyclo-[3.3.1]nonane N-oxyl)/HNO3, for the aerobic oxidation of substituted furans to cis-2-ene-1,4-diones under mild reaction conditions using oxygen as the oxidant. The catalyst system is amenable to various substituted (mon-, di-, and tri-) furans and tolerates diverse functional groups, including cyano, nitro, naphthyl, ketone, ester, heterocycle, and even formyl groups. Based on the control and 18O-labeling experiments, the possible mechanism of the oxidation is proposed.