An efficient construction of bridged chiral tetracyclic indolidines, a core structure of asperparaline, via stereocontrolled catalytic Pauson–Khand reaction

A reaction of chiral enyne derived from l-proline with a catalytic amount of cobalt (0) octacarbonyl in the presence of N-methylmorphorine N-oxide gave tricyclic enone in 54% yield (73% based on consumed starting material). Treatment of enone with aqueous methylamine followed by silica gel afforded bridged tetracyclic indolidine , a common structural motif of natural metabolites, an asperparaline series of compounds and also a potential intermediate for the synthesis of a paralytic alkaloid, asperparaline C (), in 70% yield.