There is described a process for the preparation of a compound of formula I ##STR1## in which process: a) a compound of formula II ##STR2## is reacted with an organolithium compound of formula III Li--R.sub.7 (III) b) the resulting lithium complex is reacted with a compound of formula IV Y.sub.1 --CO--CO--Y.sub.1 IV to form a compound of formula V ##STR3## c) that compound is, in either order, c1) oximated with O-methylhydroxylamine; or oximated with hydroxylamine and then methylated or fluoromethylated or difluoromethylated; c2) reacted with a chloroformic acid ester. X, m, Y, R.sub.1 to R.sub.3 and R.sub.7 are as defined in the description.