A process for preparing compounds of the formula: wherein R2 is lower alkyl; or phenyl optionally substituted by from one to five groups, the same or different, which are lower alkyl, lower haloalkyl, halogen or —SR4; R3 is halogen, lower alkyl, lower haloalkyl, lower alkoxy, lower haloalkoxy, —S-alkyl, cycloalkyl having from 3 to 7 carbon atoms in the ring, alkenyl or alkynyl having from 3 to 7 carbon atoms, or —(CR5R6)—SR2 wherein q is one or two; R4 is lower alkyl; R5 and R6 independently represent hydrogen, lower alkyl or lower haloalkyl; and n is zero or an integer from one to three; intermediate compounds of the formula: and processes for preparing them.