Environmentally Benign Procedures for the Preparation and Isolation of 3‐Methylcyclopent‐2‐en‐1‐one.

A moderately yielding (50±4%) method for obtaining 3-methylcyclopent-2-en-1-one from hexane-2,5-dione in ≥99·5% purity was developed, using 2·1% (w/v) of aqueous KOH at reflux. However, the yield was increased to 80±5% by using considerably lower concentrations of base (<0·1%) and higher temperature (200°C) with a conventionally heated autoclave or a microwave batch reactor. The preparation was scaled up with a larger autoclave and also with a continuous flow microwave reactor. The dione impurity was removed from the enone by preferential adsorption on an anion-exchange resin in the bisulfite form. The product was recovered from the aqueous phase with a hydrophobic resin. This environmentally benign, non-extractive isolation method has potential for broad applicability in cleaner production.