Intermolecular and Intramolecular Pauson–Khand Reactions of Functionalized Allenes

Pauson–Khand reactions of functionalized allenes with different alkynes give cyclopentenones with generally high regio‐ and stereoselectivities. The allenes react through their external double bonds, giving cyclopentenones with exocyclic double bond at their β positions and predominantly with E stereochemistry. Some intramolecular reactions with allenynes connected through aromatic rings are described. These give the corresponding heterocycles with moderate to good yields.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)