Pauson–Khand reaction

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The Pauson–Khand reaction is a chemical reaction that forms a cyclopentenone from an alkyne, an alkene, and carbon monoxide. This reaction is named after its discoverers, Peter L. Pauson and Ira U. Khand, who first reported it in 1973. The Pauson–Khand reaction is a valuable tool in organic synthesis due to its ability to construct complex, polycyclic structures in a single step.

Mechanism

The mechanism of the Pauson–Khand reaction involves the formation of a metal complex with a transition metal, typically cobalt. The reaction proceeds through the following steps:

1. Formation of a cobalt-alkyne complex.
2. Coordination of the alkene to the cobalt-alkyne complex.
3. Insertion of carbon monoxide into the metal-alkyne bond.
4. Cyclization to form the cyclopentenone product.

Variants

Several variants of the Pauson–Khand reaction have been developed to improve its efficiency and expand its scope. These include:

• The use of different transition metals such as rhodium and iridium.
• The use of chiral ligands to induce enantioselectivity.
• The development of intramolecular versions of the reaction, where the alkyne and alkene are part of the same molecule.

Applications

The Pauson–Khand reaction is widely used in the synthesis of natural products and complex organic molecules. Some notable applications include:

• The synthesis of steroids and terpenes.
• The construction of polycyclic frameworks in pharmaceuticals.
• The formation of key intermediates in the synthesis of bioactive compounds.

See also

• Cycloaddition
• Transition metal catalysis
• Organic synthesis
• Carbonylation