Visible-light-driven copper-catalyzed aerobic oxidative cascade cyclization of N-tosylhydrazones and terminal alkynes: regioselective synthesis of 3-arylcoumarins

Abstract

We present the first example of sustainable, intuitive, highly regioselective, visible-light-driven copper catalyzed aerobic oxidative cascade cyclization of N-tosylhydrazones with terminal alkynes for the preparation of 3-arylcoumarins at room temperature. This operationally simple methodology has been successfully applied to a wide range of N-tosylhydrazones and alkynes (49 examples), and proceeds well to afford biologically active compounds, such as monoamine oxidase B (MAO-B) inhibitor and horseradish peroxidase (HRP) inhibitor, in satisfactory yields under mild conditions. Furthermore, mechanistic studies suggest that the reaction proceeds via a copper(II)-superoxo or -peroxo complex mediated oxidative annulation of terminal alkynes, as evidenced by ¹⁸O₂ isotopic-labelling experiments.