An alternative preparation of the intermediate carboxylic acids of formula (22) of Scheme VII wherein Y is as defined above and R4 is other than hydrogen, is outlined in Scheme VIII. The organotin reagent of formula (25) is reacted in a Stille coupling reaction with an appropriately substituted aryl (heteroaryl) halide, preferably a bromide or iodide of formula (28) in the presence of a catalyst s