Route (4): The reaction of a compound of general formula (IIIg) where all symbols are as defined earlier with a compound of general formula (IIIf) where all symbols are as defined earlier and L1 is a leaving group such as halogen atom, p-toluenesulfonate, methanesulfonate, trifluoromethanesulfonate and the like, preferably a halogen atom to produce a compound of general formula (III) may be carrie