The invention relates to a process for the preparation of a compound of formula (I), wherein R1, R2 and R3 are as defined in claim 1, which process comprises a) adding a compound of formula (II), in the presence of an inert organic solvent to a mixture comprising an organic nitrite of formula (III) (R4—O—N═O (III)), wherein R4 is C1-C8alkyl, a compound of formula (IV), and an inert organic solvent; b) reacting the resulting compound of formula (V), with H2N—O—CH3 to the compound of formula (VII), c) reducing the compound of formula (VII) to the compound of formula (VIII), d) and reacting the compound of formula VIII with a compound of formula (IX), in which R* is halogen, hydroxy or C1-6 alkoxy, to the compound of formula (I).