Herein, rhodium(III)-catalyzed C-H activation/subsequent [4 + 1] cyclization reactions between benzamides and propargyl alcohols are reported in which propargyl alcohols serve as unusual one-carbon units. This title transformation led to a series of isoindolinones bearing a quaternary carbon with moderate to good yields without the requirement for external metal oxidants. Due to the mild and simple reaction conditions, this reaction is compatible with various functional groups.