Oxidative rearrangement of quinochalcones. Part 2. A facile synthesis of linderone

Abstract

Friedel-Crafts acylation of 1,2,3,5-tetramethoxybenzene in diethyl ether afforded besides the acetophenone (6a), an abnormal product shown to be 3-ethoxy-2-hydroxy-4,6-dimethoxy-acetophenone (6b). Methylpedicinin (1b), prepared from compound (6a), was found to react with acetic anhydride–DMSO, yielding linderone acetate (3d), linderone cinnamate (3e), the ester (9), and the ylide (10a). The acetate (3d) was readily hydrolysed to linderone (3b).

Reaction of quinochalcone (1e) with acetic anhydride–DMSO gave, on the other hand, the ylide (10b) as the major product besides the ester (9). A trace amount of a butenolide was also isolated and shown to be a mixture of the Z- and E- isomers (2c) and (2d). Electronic and steric factors are invoked to rationalize the different reaction pathways of quinochalcones (1a), (1b), and (1e).