Benzylideneacetone

Benzylideneacetone can be efficiently prepared by the NaOH-induced condensation of the readily available reagents acetone and benzaldehyde:[3]

CH₃C(O)CH₃ + C₆H₅CHO → C₆H₅CH=CHC(O)CH₃ + H₂O

However, the benzylideneacetone formed via this reaction can undergo another Claisen-Schmidt condensation with another molecule of benzaldehyde to form dibenzylideneacetone. Because relatively weak bases such as NaOH make very little of the enolate ion at equilibrium, there is still a lot of unreacted base left in the reaction mixture, which can go on and remove protons from the alpha carbon of benzylideneacetone, allowing it to undergo another Claisen-Schmidt condensation and make dibenzylideneacetone.[4]

If, on the other hand, lithium diisopropylamide (LDA) is used as the base, all of the acetone will deprotonated, making enolate ion quantitatively. Therefore, the most efficient way to make benzylideneacetone is to use equimolar amounts of LDA (in THF), acetone, and benzaldehyde. The reaction must be done with anhydrous chemicals as LDA breaks down in water.[5]

As with most methyl ketones, benzylideneacetone is moderately acidic at the alpha position, and it can be readily deprotonated to form the corresponding enolate[6]

The compound undergoes the reactions expected for its collection of functional groups: e.g., the double bond adds bromine, the heterodiene adds electron-rich alkenes in Diels-Alder reactions to give dihydropyrans, the methyl group undergoes further condensation with benzaldehyde to give dibenzylideneacetone, and the carbonyl forms hydrazones. It reacts with Fe₂(CO)₉ to give (benzylideneacetone)Fe(CO)₃, a reagent for transferring the Fe(CO)₃ unit to other organic substrates.[7]

• Hydrogenation of benzylideneacetone results in a preparation of benzylacetone.
• The reaction of 4-Hydroxycoumarin with this compound yields Warfarin.