In recent years, there are many reports about the synthesis of oxindoles by radical addition-cyclization. Most of these approaches are catalyzed by different transition metals, or under metal-free and photoredox catalysis conditions using N-arylacrylamides as main substrates. These methods have been a powerful strategy to obtain oxindoles in organic synthesis. At present, the studies on the synthesis of oxindoles by radical addition-cyclization are mainly focused on the types of radicals and the reaction mechanisms. This review will summarize the recent progress of the synthesis of oxindoles by radical addition-cyclization according to the different catalyst systems.

In nonaqueous medium, a series of troxerutin amidation analogues were synthesized by the reaction of vinyl-troxerutin esters with fatty amines. The influence parameters including enzyme source, the amount of the enzyme, reactive medium, water content of solvents and reaction time were investigated. The results showed that the amidation occurred regioselectively at vinyl-ester bond. Using pyridine as solvent (water content ＜1%), the amidation reaction catalyzed by lipase LS-10 (20 mg/mL) reached plateau after 21 h at 50 ℃.