Process for the preparation of compounds of the formula: in which R 1 and R 2 are identical or different and are, independently of one another, hydrogen, C 1 -C 15 -alkyl, C 6 -C 24 -aryl, C 1 -C 15 -alkoxy, C 2 -C 10 -alkenyl, C 6 -C 24 -aryloxy, C 7 -C 15 -arylalkyl, C 1 -C 15 -alkylthio, C 1 -C 15 -mono- and dialkylamino, C 6 -C 24 -mono- and diarylamino or 5- to 8-membered saturated or unsaturated heterocyclyl, which in addition can be substituted by radicals chosen from the group consisting of C 1 -C 15 -alkyl, C 2 -C 10 -alkenyl, C 1 -C 15 -alkoxy, C 6 -C 24 -aryl, C 7 -C 15 -arylalkyl, C 1 -C 15 -alkylthio, halo, hydroxyl, cyano, nitro, amino, carboxyl, C 1 -C 15 -haloalkyl, C 2 -C 10 -haloalkenyl, C 1 -C 15 -haloalkoxy, C 1 -C 15 -haloalkylthio and 5- to 8-membered saturated or unsaturated heterocyclyl, or R 1 and R 2 together form a carbocyclic or heterocyclic and saturated or unsaturated 4- to 8-membered ring which in addition can be substituted by radicals chosen from the group consisting of C 1 -C 15 -alkyl, C 2 -C 10 -alkenyl, C 1 -C 15 -alkoxy, C 6 -C 24 -aryl, C 7 -C 15 -arylalkyl, C 1 -C 15 -alkylthio, halo, hydroxyl, cyano, nitro, amino, carboxyl, C 1 -C 15 -haloalkyl, C 2 -C 10 -haloalkenyl, C 1 -C 15 -haloalkoxy, C 1 -C 15 -haloalkylthio and 5- to 8-membered saturated or unsaturated heterocyclyl, and R 3 is C 1 -C 15 -alkoxy, C 1 -C 15 -mono- and dialkylamino, C 1 -C 15 -alkylthio, C 6 -C 24 -aryloxy, C 6 -C 24 -mono- and diarylamino and 5- to 8-membered saturated or unsaturated heterocyclyl which is connected via a heteroatom, which in addition can be substituted by radicals chosen from the group consisting of C 1 -C 15 -alkyl, C 2 -C 10 -alkenyl, C 1 -C 15 -alkoxy, C 1 -C 15 -alkylthio, C 6 -C 24 -aryl, C 7 -C 15 -arylalkyl, halo, hydroxyl, cyano, nitro, amino, carboxyl, C 1 -C 15 -haloalkyl, C 2 -C 10 -haloalkenyl, C 1 -C 15 -haloalkoxy, C 1 -C 15 -haloalkylthio and 5- to 8-membered saturated or unsaturated heterocyclyl, in which compounds of the formula: in which R 1, R 2 and R 3 have the abovementioned meanings and X is Cl, Br, I or a pseudohalogen, are reacted in the presence of at least one base selected from the group of alkaline earth or alkali metal hydroxides, carbonates, hydrogenphosphates and phosphates and in the presence of at least one polymerization inhibitor to give compounds of the formula. in which R 1 and R 2 are identical or different and are, independently of one another, hydrogen, C 1 -C 15 -alkyl, C 6 -C 24 -aryl, C 1 -C 15 -alkoxy, C 2 -C 10 -alkenyl, C 6 -C 24 -aryloxy, C 7 -C 15 -arylalkyl, C 1 -C 15 -alkylthio, C 1 -C 15 -mono- and dialkylamino, C 6 -C 24 -mono- and diarylamino or 5- to 8-membered saturated or unsaturated heterocyclyl, which in addition can be substituted by radicals chosen from the group consisting of C 1 -C 15 -alkyl, C 2 -C 10 -alkenyl, C 1 -C 15 -alkoxy, C 6 -C 24 -aryl, C 7 -C 15 -arylalkyl, C 1 -C 15 -alkylthio, halo, hydroxyl, cyano, nitro, amino, carboxyl, C 1 -C 15 -haloalkyl, C 2 -C 10 -haloalkenyl, C 1 -C 15 -haloalkoxy, C 1 -C 15 -haloalkylthio and 5- to 8-membered saturated or unsaturated heterocyclyl, or R 1 and R 2 together form a carbocyclic or heterocyclic and saturated or unsaturated 4- to 8-membered ring which in addition can be substituted by radicals chosen from the group consisting of C 1 -C 15 -alkyl, C 2 -C 10 -alkenyl, C 1 -C 15 -alkoxy, C 6 -C 24 -aryl, C 7 -C 15 -arylalkyl, C 1 -C 15 -alkylthio, halo, hydroxyl, cyano, nitro, amino, carboxyl, C 1 -C 15 -haloalkyl, C 2 -C 10 -haloalkenyl, C 1 -C 15 -haloalkoxy, C 1 -C 15 -haloalkylthio and 5- to 8-membered saturated or unsaturated heterocyclyl, and R 3 is C 1 -C 15 -alkoxy, C 1 -C 15 -mono- and dialkylamino, C 1 -C 15 -alkylthio, C 6 -C 24 -aryloxy, C 6 -C 24 -mono- and diarylamino and 5- to 8-membered saturated or unsaturated heterocyclyl which is connected via a heteroatom, which in addition can be substituted by radicals chosen from the group consisting of C 1 -C 15 -alkyl, C 2 -C 10 -alkenyl, C 1 -C 15 -alkoxy, C 1 -C 15 -alkylthio, C 6 -C 24 -aryl, C 7 -C 15 -arylalkyl, halo, hydroxyl, cyano, nitro, amino, carboxyl, C 1 -C 15 -haloalkyl, C 2 -C 10 -haloalkenyl, C 1 -C 15 -haloalkoxy, C 1 -C 15 -haloalkylthio and 5- to 8-membered saturated or unsaturated heterocyclyl, in which compounds of the formula: in which R 1, R 2 and R 3 have the abovementioned meanings and X is Cl, Br, I or a pseudohalogen, are reacted in the presence of at least one base selected from the group of alkaline earth or alkali metal hydroxides, carbonates, hydrogenphosphates and phosphates and in the presence of at least one polymerization inhibitor to give compounds of the formula. in which R 1, R 2 and R 3 have the abovementioned meanings and X is Cl, Br, I or a pseudohalogen, are reacted in the presence of at least one base selected from the group of alkaline earth or alkali metal hydroxides, carbonates, hydrogenphosphates and phosphates and in the presence of at least one polymerization inhibitor to give compounds of the formula.