A solution of tert-butyl ((1S)-3-diazo-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl) carbamate (592 mg, 2.0 mmol) in 1,4-dioxane (7 mL) was placed under an atmosphere of N2 and cooled to 0 °C.