The compound of claim 1 in which Y is phenyl; and X is a bond or is chosen from --X.sub.1OX.sub.2-- and C.sub.4-6heteroarylene; wherein X.sub.1 and X.sub.2 are independently chosen from a bond and C.sub.1-3alkylene; wherein anyheteroarylene of X is optionally substituted by a member of the group chosen from halo and C.sub.1-6alkyl.4.