Flexible Synthesis of Benzofuranones from ortho-Alkynyl Phenols or Benzofurans

Benzofuranones are attractive synthetic targets in medicinal and natural products. The cycloisomerization of o-alkynyl phenol to benzofuran-3(2H)-one is reported here using gold(I) and Selectfluor. This benzofuranone can also be obtained from benzofuran without a gold catalyst. This study presents two appealing synthetic methods for benzofuran-3(2H)-ones that use readily available starting materials, have high chemoselectivity and operate under very mild conditions.