A preferred method for preparing the compounds is by acylation of an aryl amine of the formula H2 NR4 with an appropriately substituted benzoic acid derivative according to the following sequence: ##STR26## wherein R1, R2, R3 and R4 are as defined above, and L is a good leaving group, for example lower alkanolyloxy such as formyloxy or acetoxy, halide such as chloro, bromo or iodo, or an activated