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.