Electrocatalytic Dehydrogenative Lactonization of Benzylic Alcohols: A Sustainable Access to Phthalides via N-hydroxyphthalimide Mediation

Abstract

A sustainable and efficient electrochemical method for the direct oxidative lactonization of benzylic alcohols, enabling rapid access to isobenzofuran-1(3H)-ones (phthalides) is presented. This electrocatalytic transformation leverages N-hydroxyphthalimide as a redox mediator under mild, metal-free conditions, offering an environmentally friendly alternative to traditional oxidation protocols. The method demonstrates broad substrate scope and delivers phthalide derivatives consistently in good to excellent yields. Mechanistic studies, combining cyclic voltammetry and density functional theory calculations, support a radical-mediated hydrogen atom transfer mechanism driven by phthalimide-N-oxyl radicals. Importantly, the utility of the protocol extends beyond model substrates: it is successfully applied to the synthesis of pharmaceutically relevant compounds, including talopram and a key intermediate for a neuropeptide Y5 receptor antagonist. Overall, this work underscores the power of electrosynthesis in modern organic chemistry, merging green chemistry principles with synthetic efficiency.