5 g of (2R)-2,3-dihydro-1,4-benzodioxin-2-carboxylic acid (27.8 mmol) are dissolved in 300 ml of acetonitrile. 6 g of N,N′-dicyclohexylcarbodiimide (29.1 mmol) and then 4.1 g of 1-hydroxybenzotriazole (30.6 mmol) are added. Finally, 6.2 g of tert-butyl piperazine-1-carboxylate (33.4 mmol) are added and stirring is carried out for 12 hours at ambient temperature. The reaction mixture is subsequently filtered and the filtrate is then evaporated to dryness. The oil thereby obtained is purified by flash chromatography on silica (eluant: toluene/ethyl acetate 80/20) to yield the expected product in the form of an oil.
