Unexpected Brønsted Acid-Catalyzed Domino Reaction of 3-Hydroxyisoindolin-1-ones and<i>N</i>-<i>tert</i>-Butyl Hydrazones for the Synthesis of 3-(Hydrazono)isoindolin-1-ones
3‐(Hydrazono)isoindolin‐1‐one derivatives were synthesized in excellent yields and high chemoselectivities by a Brønsted acid‐catalyzed domino reaction between 3‐hydroxyisoindolin‐1‐ones and N‐tert‐butyl hydrazones. The E‐configuration of the hydrazone products was determined by X‐ray single‐crystal diffraction.