Ethylenediamine → 2-Piperazinone, 3,3-dimethyl-

A mixture of ethyl-2-bromoisobutyrate (14.6 g, 74.9 mmol), ethylene diamine (33 mL, 487 mmol, 6.5 equiv) and potassium carbonate (11.4 g, 82.4 mmol, 1.1 equiv) in toluene (150 mL) was stirred for 22 h at reflux, cooled and filtered. The filtrate was concentrated and the residue triturated in Et2O to afford 6.3 g of 3,3-dimethyl-piperazin-2-one as a white solid. Methyl iodide (4 mL, 64.0 mmol, 1.3 equiv) was added dropwise to a suspension of 3,3-dimethyl-piperazin-2-one (6.3 g, 49.2 mmol) and potassium carbonate (8.8 g, 64.0 mmol, 1.3 equiv) in DME (20 mL). The reaction mixture was heated to 45° C., stirred for 3 h, cooled and filtered, washing the filter cake with DME. The filtrate was concentrated and the residue triturated in DME to afford 2.8 g (batch 1) of the title compound as a white solid. The filtrate from the trituration was concentrated and the residue purified by silica gel column chromatography (DCM/MeOH, 9:1) to afford 1.75 g (batch 2) of the title compound as a white solid. Title compound: ESI-MS: 143.1 [M+H]+; TLC: Rf=0.25 (DCM/MeOH, 9:1).