There are still some synthetic chemists who hesitate to use metal-mediated or -catalysed reactions. The Pauson-Khand reaction (PKR) is a powerful transformation that has now been sufficiently well developed to be routinely considered when planning a synthesis, especially of polycyclic complex molecules. This tutorial review aims to encourage the use of this process explaining the best ways of performing a PKR both in the stoichiometric and the catalytic version, showing the scope of the process and its limitations. Additionally, asymmetry can be introduced in the reaction using several strategies, which will be discussed. The most recent examples of the synthetic applications of the PKR in natural product synthesis will give the reader an idea of the great usefulness of this reaction.

The Pauson−Khand reaction still has a relatively low scope with respect to the used carbon skeleton, while yields are low in many other cases. We have observed that the addition of molecular sieves improves yields remarkably. Experimental protocol is extremely easy, and it has been applied to several substrates including the less favorable ones.

Pauson-Khand reactions are carried out with different substituted aromatic enynes, yielding tricyclic cyclopentenones related to natural products such as chromenes. Enynes are easily obtained in a two-step approximation from the corresponding salicylaldehydes. The reaction is promoted by dissolved TMANO (trimethylamine N-oxide) and/or 4 A molecular sieves. This new way of induction for the Pauson-Khand reaction increases yields remarkably, allowing the reaction of some substituted alkenes which fail to react in the absence of the zeolite. Isomerization of the double bond of the cyclopentenone ring is observed except when nonterminal triple bonds are used. For trisubstituted alkenes, an interrupted Pauson-Khand process is observed with moderate yields.

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