A sequential continuous-flow system to produce 3-aryl benzofuranones was developed. Starting from 2,4-ditert-butylphenol and glyoxylic acid monohydrate, both the initial cyclocondensation and the subsequent FriedelÀ Crafts alkylation were catalyzed by the same heterogeneous catalyst, Amberlyst-15H. The catalyst has a promising lifetime for these two steps, and it was able to be recovered and reused for several runs without deactivation. By using the established flow system, 5,7-di-tert-butyl-3-(3,4-dimethylphenyl)-3H-benzofuran-2-one (Irganox HP-136), which is a commercial antioxidant, was prepared in 88% two-step yield. Reactions with various aromatic compounds proceeded well under flow conditions to afford 3-aryl benzofuranone derivatives in high yields with good functional group compatibility.

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