| abstract |
The present invention relates to a novel process for the preparation of a compound of formula (I), wherein R 1 , R 2 , R 3 , R 4 and R 5 are each independently selected from hydrogen, halogen, C 1 -C 4 -alkyl, C 1 -C 4 -haloalkyl, C 1 -C 4 -alkoxy, C 1 -C 4 -haloalkoxy, nitro, cyano, and pentafluorothio; R 6 is C 1 -C 4 -alkyl, or C 1 -C 4 -haloalkyl; by oxidation of a compound of formula (II) with an oxidation agent selected from trifluoroperacetic acid and trichloroperacetic acid in the presence of a catalyst selected from hydroxides, oxides, sulfates, acetates or trifluoroacetates of lithium, magnesium, calcium, strontium, barium, titanium (IV), zinc (II) and manganese (II). |