To a solution mixture of 5-benzyloxy-6-hydroxy-2-(1-naphthalen-1-yl-cyclopentylmethyl)-pyrimidine-4-carboxylic acid (2-hydroxyethyl)-amide (347) (140 mg, 0.28 mmol) and diisopropyl azodicarboxylate (0.28 mL, 1.41 mmol) in dichloromethane (70 mL) was added triphenyl phosphine (443 mg, 1.69 mmol) at room temperature and the reaction mixture was stirred for 15 min at the same temperature. The yellow color disappeared (silica TLC, ethyl acetate 100%; Rf=0.2). The dichloromethane was removed in vacuum to get 9-benzyloxy-6-(1-naphthalen-1-yl-cyclopentylmethyl)-3,4-dihydro-2H-pyrazino[1,2-c]pyrimidine-1,8-dione (348) (650 mg, crude) which was used directly in the next step without purification.
