Construction of quaternary centres for natural polycycles: The Pauson–Khand approach

Construction of quaternary carbons is a challenge in PK chemistry, with few precedents in the literature. Starting from suitable functionalized enynes including an aromatic ring that templates the reaction, polycyclic ketones are obtained with a quaternary carbon. Special reaction conditions are necessary including the use of molecular sieves and co-catalysis with rhodium complexes jointly with cobalt carbonyl. The products obtained are intermediates in the synthesis of various natural products like the Hamigeran family and the steroidic alkaloid Conessine.