SYNTHESIS OF NATURALLY OCCURRING CURCUMINOIDS AND RELATED COMPOUNDS

Six known naturally occurring curcuminoids1) like curcumin, [5-hydroxy-1,7-bis(4-hydroxy-3-methoxyphenyl)-1,4,6-heptatrien-3-one (4a)] and 31 other analogs (Scheme 1) have been synthesized. Among them, 25 curcuminoids were prepared by condensing different substituted 2,4-pentanediones and benzaldehydes. The boron complex 12 has been used to avoid Knoevenagel condensation at C-3 of 2,4-pentanedione. Some curcuminoids containing hydroxy groups in the aromatic moiety have been acylated. Alkylation of the tetrabutylammonium salt of 5-hydroxy-1,7-diphenyl-1,4,6-heptatrien-3-one (1a) by benzyl bromide gave only C-alkylated 4-benzyl-1,7-diphenyl-1,6-heptadiene-3,5-dione (1d*). The 13C NMR data, the UV absorptions, and the tautomerism of the curcuminoids are discussed.