Compounds of formula (VI) where R1 represents group (A) may conveniently be prepared by cyclising a compound of formula (VII): ##STR10## in which (i) A represents a group convertible to COCl and B represents --(CH2)j L1 where L1 is a leaving group or A and L1 together represent --COO--; one of j, k and l is 1 and the other two independently represent an integer of 2 to 4. and R10 represents hydrog