5-Benzyloxy-2-[1-(4-chlorophenyl)-cyclopentylmethyl]-6-hydroxypyrimidine-4-carboxylic acid cyclopropyl-(2-hydroxyethyl)-amide (326) (90 mg, 0.17 mmol) and triphenylphosphine (90.5 mg, 0.35 mmol) were taken up in dichloromethane (3 ml) at room temperature followed by the slow addition of diisopropyl azodicarboxylate (52.34 mg, 0.26 mmol) and stirring for 1 h. Dichloromethane (15 ml) was added to the reaction mixture, which was subsequently washed with water (10 ml) and brine (10 ml). The organic part was dried and concentrated under reduced pressure. The obtained residue was purified by normal silica column using 30% ethyl acetate in hexane to get 9-benzyloxy-6-[1-(4-chlorophenyl)-cyclopentylmethyl]-2-cyclopropyl-3,4-dihydro-2H-pyrazino[1,2-c]pyrimidine-1,8-dione (327) (130 mg, 56%; 2 steps) as a sticky yellow solid.
