Unusual anthocyanin reaction with acetone leading to pyranoanthocyanin formation

Anthocyanins undergo unusual facile reactions with acetone to give rise to pyranoanthocyanins, thus showing that the new class of pigments isolated fr om blackcurrant seeds were a result of solvent participation. This oxidativ e addition was extended to the successful synthesis of pyranomalvidin or 2- (3,5-dimethoxy-4-hydroxyphenyl)-8-hydroxy-5-methyl-3-O-beta -D-glucopyranos yl- oxypyrano[4,3,2-de]-1-benzopyrylium by the reaction of the principal gr ape anthocyanin malvidin 3-O-glucoside with acetone. The chemical structure s of pyranomalvidin, together with pyranocyanin B and pyranodelphinin B, we re fully characterised by 2D NMR. (C) 2001 Elsevier Science Ltd. All rights reserved.