The Pauson-Khand reaction cycloadditions of olefins, acetylenes, and CO

3 The Pauson-Khand Reaction Cycloadditions of Olefins, Acetylenes, and CO 

In the presence of octacarbonyldicobalt, three-component cycloaddition of acetylenes occurs with alkenes and carbon monoxide, affording cyclopentenones. Although thermal activation of the organometallic was the original method of effecting this transformation, a variety of reaction additives have since been explored, resulting in procedures that permit the 

Pauson-Khand process to occur at room temperature or below. Similarly, although most examples use stoichiometric cobalt, important progress has been made toward rendering this reaction catalytic in the metal. In addition, a large body of information exists to enable the chemist to apply the Pauson-Khand to synthetic problems with good confidence as to the outcome, both in terms of overall yield as well as stereo- and regioselectivity [81]. 

Several other transition metal processes give cyclopentenones from similar substrates. Although none of these has yet been shown to possess the scope of the Pauson-Khand, many have advantages that make them valuable alternatives. The interested reader is directed to the literature citations for further information [82-88]. 

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