The cobalt catalyzed formation of cyclopentenones from alkenes, alkynes and carbon monoxide is known as the Pauson-Khand reaction. The precise mechanism has not yet been fully elucidated, but previous studies have demonstrated that the larger alkyne substituent ends up next to the carbonyl group in the product. The regioselectivity with respect to an acyclic alkene is less predictable in intermolecular reactions, but reactions with cyclic alkenes are highly stereoselective. Intramolecular reactions proceed with both excellent regio- and stereoselectivity.

• Reagents: Catalytic Transition Metal Complex (Co₂(CO)₈, Fe(CO)₅, Ru₂(CO)₁₂, etc.), CO
• Reactant: Terminal or Internal Alkyne, Mono-, Di- or Trisubstituted Alkene
• Product: Substituted Cyclopentenone
• Type of Reaction: [2+2+1] Cycloaddition

Lab Tips

This reaction requires high temperatures and long reaction times. Microwave irradiation instead of classical heating reduces reaction times; however, note that some studies suggest that NaOAc is not effective when using microwave irradiation and other bases should be considered. Moreover, studies suggest that if sodium acetate is used, it should be anhydrous.

Mechanism

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Related Reactions

Related Compounds