(VII): ##STR9##wherein R.sup.2, R.sup.4 -R.sup.10 are as hereinbefore defined and L is a leaving group, or b) cyclising a compound of the formula (VIII): ##STR10##wherein R.sup.2, R.sup.4 -R.sup.10 as hereinbefore defined and R.sup.11 -R.sup.13 are independently selected from C.sub.1-6 alkoxy, aryloxy, di-C.sub.1-6 alkylamino and diarylamino or any two of R.sup.11 -R.sup.13 represent o-phenylened