Compounds of general formula IJ, wherein B is other than a sulphur atom, Z is other than an ethynylene group and a grouping of the formula: ##STR32## and the other symbols are as hereinbefore defined, may be prepared by reduction of compounds of general formula IK, wherein B is other than a sulphur atom, Z is other than an ethynylene group and a grouping of the formula: ##STR33## and the other sym