Compounds of general formulae I and II, in which R1 is hydrogen, can be alkylated in the presence of base (e.g., hydrides, alkoxides, hydroxides of alkali or alkaline earth metals, or of organo-lithium compounds) by treatment with R1 L in which L is a leaving group such as a halogen, mesylate or tosylate to give a fused pyrrolocarbazole-6-one derivative which has an R1 group bound to the lactam ni