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).