Investigation of the synthesis of angular tricyclic compounds by intramolecular Pauson–Khand reaction of exo- and endo-cyclic enynes

Intramolecular Pauson–Khand reaction of various alkynyl exo-alkylidene-cyclohexanes and -pentane gives angular type 6–5–5 and 5–5–5 tricyclic compounds in good to high yield. The present reaction also offers convenient construction of two contiguous quaternary centers, which could not be synthesized from alkynyl endo-cycloolefins. Scope and limitation of the present reaction of various exo- and endo-cyclic enynes are also described.