Rhodium(III)-Catalyzed C–H Functionalization of 1‑(2H)‑Phthalazinones at C8

The rhodium­(III) catalyst tris­(acetonitrile)­pentamethylcyclopentadienylrhodium­(III) hexafluoroantimonate ([Cp*Rh­(MeCN)₃]­(SbF₆)₂) reacts with 1-(2H)-phthalazinones to promote a C–H functionalization event at C8. Preparation of a set of compounds arising from oxidative alkenylation with olefins, hydroarylation with alkynes, and iodination with N-iodosuccinimide is reported here. Oxidative alkenylation proceeds in very good yield, and the scope and limitations of the hydroarylation and halogenation reactions are discussed. Notably, this strategy enables rapid preparation of C8-substituted phthalazinones without requiring phthalazinone ring synthesis starting from a prefunctionalized arene.