Tandem [2+2] Cycloaddition/Rearrangement toward Carbazoles by Visible-Light Photocatalysis

Reported herein is the first example of the synthesis of carbazoles via oxidative cyclization of 3-alkenylindoles with styrenes under visible light. The irradiation of a catalytic amount of [Ir(dtbbpy)(ppy)(2)][PF6] as the photocatalyst enables various 3-alkenylindoles and styrenes to undergo tandem [2 + 2] cycloaddition/rearrangement, thereby leading to carbazole derivatives in good to excellent yields under aerobic conditions. Mechanistic studies reveal that photoinduced energy transfer followed by electron transfer is responsible for the tandem reaction.

Automated summary

This study presents the first example of synthesizing carbazoles through oxidative cyclization of 3-alkenylindoles with styrenes under visible light. Using [Ir(dtbbpy)(ppy)(2)][PF6] as the photocatalyst enables the tandem reaction to proceed efficiently, leading to carbazole derivatives in good to excellent yields. The mechanistic studies suggest that the tandem reaction is driven by photoinduced energy transfer followed by electron transfer.