Pauson–Khand reaction

The Pauson–Khand reaction (or PKR or PK-type reaction) is a chemical reaction described as a [ 2+2+1 ] cycloaddition between an alkyne, an alkene and carbon monoxide to form a α,β-cyclopentenone. The original catalyst for this organic reaction was dicobalt octacarbonyl but this has since been replaced by other catalyst systems.



With asymmetrical alkenes or alkynes regioselectivity is always an issue, but less so with intramolecular reactions.



Variations
Wilkinson's catalyst based on the transition metal rhodium also effectively catalyses PK reactions but requires silver triflate as a co-catalyst.



Molybdenum hexacarbonyl is a carbon monoxide donor in PK-type reactions between allenes and alkynes with dimethylsulfoxide in toluene.



Cyclobutadiene als lends itself to a [ 2+2+1 ] cycloaddition although this reactant is generated in situ from decomplexation of stable cyclobutadiene iron tricarbonyl with CAN. .