0.011 mol of propyl isocyanate is added dropwise and with magnetic stirring to a suspension of 0.01 mol of 2-(1-naphthyl)-2-(methoxycarbonyl)ethylamine hydrochloride, obtained in stage B of Example 11, in 5 cm3 of pyridine. The reaction medium is stirred for 1 hour at a temperature of 80° C. and then poured into ice-cold water. The mixture is acidified with 1N hydrochloric acid solution. The precipitate formed is drained, washed with water, dried and then recrystallized in a toluene/cyclohexane mixture.
