Investigation of the Intermolecular Pauson-Khand Reaction of Various 1-Alkynes with Cyclic exo-methylene Compounds

Intermolecular Pauson-Khand reaction of various 1-alkynes with 4exo-methylenepiperidine and -cyclohexane derivatives to give corresponding spirocyclopentenones was investigated.The reaction of m-and p-substituted arylalkynes furnished corresponding spirocyclic compounds in good yields, while that of o-substituted arylalkynes and 1-hexyne proceeded in nil to moderate yield.Synthesis of spirobicyclic compounds has been focused because of their important utilities for total synthesis of natural products. 1Thus, several synthetic methodology of them has been developed. 2In connection with our studies 3 on intramolecular Pauson-Khand reaction of exo-cyclic enynes, intermolecular version of the reaction of 1-alkynes with exo-cyclic olefins suggested a facile approach to spirobicyclic compounds with cyclopentenone sub-unit.Contrary to the extended studies 4 on intermolecular Pauson-Khand reaction with endo-cyclic olefin, the similar reaction with exo-cyclic olefin was performed only with small ring systems such as methylenecyclopropanes and -butanes. 5Here, we describe our full accounts on intermolecular Pauson-Khand reaction of various 1-alkynes with exo-cyclic olefins to give 6-5 spirocyclic compounds.