A mixture of 0.400 g (0.002 mol) of 6-hydroxy-quinoline-2-carboxylic acid ethyl ester, 0.966 g (0.004 mmol) of triphenylphospine (Fluka), 0.396 g (0.003 mmol) of 3-piperidin-1-yl-propan-1-ol and 0.68 ml (0.004 mmol) of di-tert.-butyl azadicarboxylate 40% in toluene in 40 ml THF was stirred for a prolonged period of time at 35° C. The mixture was filtered through a pad of silica and washed with 30 ml THF. The mixture was evaporated to dryness and purified on silica eluting with a gradient of DCM/MeOH/NH4OH from 97/3/0.5 to 90/10/0.5. The product fractions were evaporated and the residue was triturated with diethyl ether to yield after drying under vacuum 0.600 g (93%) of the title compound as white solid. MS (m/e): 343.3 (M+H)+.
