Laser Raman detection of an electrogenerated intermediate during anodic synthesis of dihydrobenzofurans via formal [3+2] cycloaddition

A phenoxonium cation intermediate was successfully observed in situ by laser Raman spectroscopy during the electro-oxidation of 4-methoxyphenol in a lithium perchlorate/nitromethane electrolyte solution as shown by the Raman bands at 1665 cm−1 and 1615 cm−1. These conditions are those used for the electrosynthesis of dihydrobenzofurans by a formal [3+2] cycloaddition when the oxidation is carried out in the presence of an olefin.