Abstract The reactivity of a range of pyridone and pyrazinone derivatives towards alkynes in the presence of cyclopentadienylcobaltbis (ethene) has been investigated. Depending on the nature of the substrates,[2+ 2+ 2]-or [2+ 2] cycloaddition, C [BOND] H, or N [BOND] H activation may occur. In the case of pyridones, the first three predominated with N-protected derivatives, whereas substrates containing N [BOND] H bonds followed an N [BOND] H ...