Cobalt metallacycles. Part 5. Synthesis of pyridines from nitriles and acetylenes via cobaltacyclopentadienes

Abstract

The complexes, [[graphic omitted]R⁴)(cp)(PPh₃)](cp =η-cyclopentadienyl) react with nitriles to give highly substituted pyridines. When R⁴= CO₂Me, nitrites react regioselectively such that the nitrogen atom in the resulting pyridine ring occupies a position away from the carbon to which the CO₂Me is attached. The reaction with 2-methylacrylonitrile gives, beside the pyridine, a cyclohexadiene derivative and its complex. The complex [Co(cp)(PhC⋮CPh)(PPh₃)] does not react with nitriles to form a nitrogen-containing cobalt metallacycle. The mechanism of the stoicheiometric and catalytic reaction is discussed.