Organic Base-Catalyzed Cascade Reaction of Electron-Deficient Cyclopentadienone with Prop-2-yn-1-ols: Formation of 3-Methylenetetrahydrofuran Ring Condensed with Cyclopentenone

2,5-Bis(methoxycarbonyl)-3,4-diphenylcyclopentadienone (1a) reacts with prop-2-yn-1-ols (2) in the presence of 1,4-diazabicyclo[2.2.2]octane at room temperature to produce bicyclic carbocycles (4) in moderate yields, as well as tetracyclic carbocycle (5).The bicyclic carbocycle, which has a 3-methylenetetrahydrofuran moiety, is derived from the anionic cyclization of the 1,4-adducts of 1a and 2 onto a non-activated alkyne.The mechanism of the cascade reaction was discussed based on the density functional theory calculations and the X-ray crystallographic analysis.