Synthetic dyes: simple and original ways to 4-substituted flavylium salts and their corresponding vitisin derivatives

Flavylium salts substituted at the 4-position have been prepared according to a Grignard reaction of some flavones with appropriate alkyl- and aryl-magnesium bromides. Among these compounds, 4-methyl flavylium salts were gently reacted with aromatic aldehydes, affording new anthocyanidin pigments, some of which are of the vitisin family. These are the first examples of chemically synthesized vitisidins (aglycones of vitisins). Compared to the more common flavylium salts, they demonstrate a large bathochromic shift (from about 100-200 nm), thus providing blue-violet and green colours, so difficult to obtain with anthocyanidins in general.