New pyrimidine and triazine intermediates for herbicidal sulfonylureas are prepared as follows: 2,4-dichloro-6-methylpyrimidine is converted via a halogenation, halogen exchange and substitution sequence to 2-amino-4-tri¯uoromethyl-6-tri¯uoromethoxypyrimidine. New ¯uoromethyl-triazines are available starting from guanidine, trichloroacetonitrile and di¯uoroacetic anhydride, or alternatively from thiocarbamoyl guanidine and chlorodi¯uoroacetic ester ring closure. To obtain new o-¯uoroalkyl-benzenesulfonamide precursors, o-chlorobenzaldehyde was ¯uorinated with sulfur tetra¯uoride, or a bromobenzene derivative was subjected to a substitution reaction with sodium penta¯uoropropionate. Sulfonylureas derived from tri¯uoromethylpyrimidines with an m-methylthio substituent are selective postemergence herbicides in cotton, presumably due to sulfone metabolization. Selectivity in wheat is obtained by combining 4-methoxy-6-tri¯uoromethylpyrimidine with a lipophilic di¯uoromethylbenzenesulfonamide moiety. Also in the di¯uoromethyl-triazine series, the combination with the di¯uoromethyl-benzenesulfonamide moiety is a good choice for wheat selectivity. Chlorodi¯uoromethyl-and tri¯uoromethyltriazines, however, combine better with an aromatic ester for best activity and selectivity in wheat. Selected compounds are undergoing broad ®eld tests in wheat.