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 a 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 the 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 a broad substrate scope and provides a practical and atom-economic approach for the synthesis of valuable α-allenol derivatives from readily available starting materials.