Revisiting curcumin chemistry part I: a new strategy for the synthesis of curcuminoids

A new strategy for the synthesis of curcuminoids is described involving the reaction of acetylacetone difluroboronite with an aromatic aldehyde in the presence of n-butylamine as catalyst. The new intermediate products, curcuminoid difluroboronites, of symmetrically substituted curcuminoids like curcumin and bisdemethoxycurcumin are stable, can be isolated and hydrolysed with aq. methanol at pH 5.8 to get the curcuminoids of high purity. The method is applicable for unsymmetrical curcuminoids like demethoxycurcumin also with some modification involving column chromatography. The intermediate curcuminoid difluroboronites, as also the natural β-diketone pongamol difluroboronite, prepared for the first time were characterized on the basis of physical and chemical properties and spectroscopic data. The advantage of using borontrifluoride to protect the enol group in acetylacetone over the generally used boric oxide is brought out. The importance of conducting biological activity studies using pure curcuminoids is explained.