Benzofuranones are heterocycles that are often found, e.g., in natural products, biologically active compounds, or dyes. 2,2-Disubstituted benzofuranone cores. for example, are present in various drugs, such as griseofulvin, maesopsin, and sulfuretin. However, existing methods for the synthesis of 2,2-disubstituted benzofuranones are often hampered by a tedious synthesis of the starting materials, low chemoselectivity, and/or harsh conditions.

Zhonghua Xia, Beijing Institute of Technology, China, and colleagues have developed two flexible methods for synthesizing benzofuran-3(2H)-ones (pictured). One protocol is a gold-catalyzed cycloisomerization of o-alkynyl phenols with alcohols or acids (pictured above in the top row). The team used Ph₃PAuCl as the catalyst, Selectfluor as an oxidant, trifluoromethanesulfonic acid (TfOH) as an additive, and MeCN as the solvent. The reactions were performed at 70 °C and the products were obtained in moderate to good yields.

The team also found that a second option is a metal-free treatment of benzofurans with alcohols, acids, or water (pictured above in the bottom row). The team left out the gold catalyst and swapped the o-alkynyl phenol substrates for benzofurans in this approach. In most cases, this approach gave the corresponding benzofuranones in higher yields than the gold-catalyzed cycloaddition reaction. Overall, the two methods provide flexible options for the synthesis of benzofuran-3(2H)-ones from easily available starting materials and with good chemoselectivity and a broad substrate scope.

• Flexible Synthesis of Benzofuranones from o‐Alkynyl Phenols or Benzofurans,
  Wenqian Du, Rongjie Yang, Jiawen Wu, Zhonghua Xia,
  Eur. J. Org. Chem. 2023.
  https://doi.org/10.1002/ejoc.202201497