AlCl₃‑Mediated Aldol Cyclocondensation of 1,6- and 1,7-Diones to Cyclopentene and Cyclohexene Derivatives

Exactly 1/3 mol of AlCl3 is sufficient to cyclize 1 mol of 1,ω-dibenzoylbutane (or pentane) to a cyclopentenone (or hexenone) derivative in high yield at room temperature in 40 min to several hours. This condensation is driven by removing elements of water as HCl and Al­(OH)3, and the product enones are exclusively unconjugated, unlike the base-catalyzed condensations providing thermodynamically more stable conjugated enones.