A solution of diethyl azodicarboxylate (0.639 g, 3.65 mM), in anhydrous tetrahydrofuran (5 ml) is added, dropwise, over a period of 0.5 hours, at room temperature to a mixture of 4,4-difluoro-3-benzylamino-butanol (0.790 g, 3.65 mM) prepared as in Step C, triphenylphosphine (0.962 g, 3.65 mM), and phthalimide (0.540 g, 3.65 mM) in tetrahydrofuran (20 ml). After stirring for 2.5 hours at room temperature, the solvent is evaporated in vacuo. The residue is taken off in benzene and the solution filtered. The solid is washed three time with benzene. The filtrate is evaporated to dryness; the residue is taken off in diethyl ether. Filtration and evaporation of the solvent in vacuo yields a yellow oil. The expected phthalimide is isolated by column chromatography (medium pressure silica gel chromatography technique, ethyl acetate/cyclohexane 2:8): 0.800 g (yield 65%).
