pared by reacting a compound of formula (III), defined above, with a compound of formula R.sup.9 .multidot.C.tbd.C.multidot.COOR.sup.10 (wherein R.sup.9 and R.sup.10 areas defined above).Where X represents a group other than a hydrogen atom, this group can be introduced into the compound simultaneously with, before or after the introduction of the substituent Y by treating the compound of formula