η5-Cyclopentadienylcobalt-Mediated Inter- and Intramolecular [2+2+2] Cycloadditions of Alkynes to Aldehydes and Ketones: A Novel Synthesis of Fused 2H-Pyrans - Harvey, Daniel F; Johnson, Barry M; Ung, Christopher S; Vollhardt, K Peter C (Synlett, 1989)