Combination of RCM and the Pauson-Khand Reaction: One-Step Synthesis of Tricyclic Structures.

The combination of ring-closing metathesis (RCM) followed by an intramolecular Pauson–Khand reaction gives direct entry to tricyclic compounds. The RCM was carried out on a hexacarbonylcobalt-complexed alkyne, this complex acting as a protecting group against enyne metathesis. The procedure was studied for dienynes containing heteroatoms and allows the building of [6,5,5] and [7,5,5] tricyclic systems. The feasibility of the process depends strongly on the nature of the substrate.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)