Pauson-Khand Reaction of Enynes Bearing exo-Olefin and Its Application to Total Synthesis of Lycopodium Alkaloid, Magellanine

Abstract

Pauson-Khand reaction (PKR) is a useful reaction for formation of cyclopentenones from alkyne-cobalt complex, which is obtained from alkynes and Co2(CO)8, and alkenes by heating the mixture or by treating the mixture with amine N-oxide at room temperature. Until now, there are many reports on PKR of both endo-cyclic and acyclic olefins, however, only a few reports on exo-olefins have appeared. Thus, the authors investigated intra- and inter-molecular PKR of exo-olefins. The intramolecular reaction of cyclic and acyclic enynes bearing exo-olefins was performed to give corresponding bi- and tri-cyclic compounds. Also, intermolecular PKR of exo-cyclic olefins with alkynes furnished spiro-bicyclic compounds. Furthermore, the present methodology was developed to construct tricyclic skeleton of Lycopodium alkaloid, magellanine family and formal total synthesis of magellanine was accomplished.