Ruthenium-Catalyzed Redox-Neutral [4 + 1] Annulation of Benzamides and Propargyl Alcohols via C–H Bond Activation

Internal alkynes have been used widely in transition-metal-catalyzed cycloaddition reactions, in which they generally serve as two-carbon reaction partners. Herein, we report ruthenium­(II)-catalyzed redox-neutral [4 + 1] annulation of benzamides and propargyl alcohols, in which propargyl alcohols act as one-carbon units. This synthetic utility of propargyl alcohols led to a series of potentially bioactive N-substituted quaternary isoindolinones with moderate to high yields under mild conditions. Without the requirement for an external metal oxidant, this title transformation is compatible with various functional groups, which further underscores its synthetic utility and versatile applicability. In addition, preliminary mechanism experiments have been conducted and a plausible mechanism is proposed.