| abstract |
The present invention relates to a process for the preparation of compounds of formula I wherein R2 and R3 are each independently of the other hydrogen or C1-C4 alkyl, a) reacting a compound of formula II where R1, R2 and R3 are as defined for formula I and X is bromine or chlorine, with a compound of formula III where R4 is hydrogen or C1-C4 alkyl, in the presence of a base and catalytic amounts of at least one complex compound of palladium, for forming a compound of formula IV where R1, R2, R3 and R4 are as defined for formula I; and b) converting that compound, using a reducing agent, into the compound of formula I. |