To a suspension of (S)-tert-butyl 2-methyl-5-thioxopiperazine-1-carboxylate (2.5 g, 10.9 mmol) in n-butanol (10 mL) was added pyrazine-2-carbohydrazide (1.6 g, 11.9 mmol) and the reaction mixture was heated to 120° C. for 12 hours. The reaction mixture as cooled to room temperature, concentrated onto silica gel and purified by flash column chromatography (0-20% MeOH in EtOAc) to provide the desired compound (1.5 g, 43%). 1H NMR (400 MHz, DMSO) δ 9.36 (d, J=1.4 Hz, 1H), 8.78-8.74 (m, 2H), 5.02 (d, J=17.4 Hz, 1H), 4.72 (d, J=12.6 Hz, 2H), 4.53 (d, J=17.4 Hz, 1H), 4.36-4.28 (m, 1H), 1.48 (s, 9H), 1.10 (d, J=6.9 Hz, 3H).
