Photoinduced copper-catalyzed cross-coupling of epoxides and alkynes via radical anions

Abstract

Epoxides are versatile intermediates in organic synthesis due to the high ring strain of their three-membered oxirane structure. While the classical two-electron ring-opening of epoxides with nucleophiles or through transition-metal catalysis is well established, single-electron reduction strategies remain underutilized. Herein, we report a photoinduced copper-catalyzed radical cross-coupling of epoxides with terminal alkynes, enabling the regioselective synthesis of multisubstituted α-allenols under mild conditions. Mechanistic studies suggest that the reaction proceeds via direct single-electron transfer (SET) from an excited state organic photocatalyst DBPP to the epoxide, generating an epoxide-derived radical anion that undergoes regioselective ring opening. Subsequent protonation forms a carbon-centered benzyl radical, which is intercepted by a BOPA–copper(II) acetylide complex to achieve cross-coupling and isomerization. This dual catalytic system avoids the use of stoichiometric iodide activators, reducing agents, or sacrificial electrodes, thus enhancing atom economy and functional-group tolerance. The methodology offers broad substrate scope and provides a practical and atom-economical approach for the synthesis of valuable α-allenol derivatives from readily available starting materials.