Pauson-Khand/Diels-Alder domino

Scheme 6/4.6. Domino Pauson-Khand/Diels-Alder reaction.

It is not quite clear which step takes place first - the Co-catalyzed [2+2+1] cycloaddition of the outer alkyne moiety, or the Diels-Alder reaction of the diene with the inner alkyne to form a 1,4-cyclohexadiene, which then undergoes a Pauson-Khand reaction with the remaining alkyne. Recently, it has been shown that a domino reaction can also be performed using 1 mol of a 1,7-diphenyl-1,6-diyne 6/4-20 and a 1,3-diene 6/4-21 in the presence of Co/C at 150 °C under 30 atm CO, to give the polycyclic compounds 6/4-22 as sole product (Scheme 6/4.7) [282]. 

In recent years, many novel MCRs - including Michael addition-initiated three-component domino sequences [10], Knoevenagel/hetero-Diels-Alder-based MCRs [11], radical chain MCRs [12], transition metal-catalyzed Pauson-Khand MCRs [13], as well as Petasis MCRs [14], have been added to the chemisf s armamentarium and successfully applied to all fields of organic synthesis. 

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