[3 + 2] cycloaddition reaction of generated in situ ketonitrone^a.

^aAll reactions were carried out with 1 (0.50 mmol), 2 (0.50 mmol), EtONa (1.3 equiv.), and DCM (5.0 mL), 12–24 h for step one, then 4 (1.5 equiv.) was added, 17–21 h for step two unless otherwise stated; isolated yield based on 1; the dr ratio is given in brackets and determined by ¹H NMR analysis (see ESI for details).

^bThe reactions were carried out with 4 mmol scale of 1d.