Polyphosphoric Acid–Mediated, One-Pot, Novel Reactions to Build Polymethoxyarylnaphthalene Lignans

Abstract

The one-pot reaction of succinic anhydride with 1,2-dimethoxybenzene furnished two structurally complicated polymethoxyarylnaphthalene lignans, polymethoxyarylnaphthol 1 as the minor product and polymethoxynaphtho[1,2-b]oxacycloheptatrienone 2 as the major product, in the presence of a small amount of polyphosphoric acid (PPA) as catalyst at 140 C and yielded 2 as a single product in good yield when a large amount of PPA as solvent was employed at 60-80 C. The novel structures of 1 and 2 were elucidated from 1 H NMR, 13 C NMR, infrared (IR), and Electrospray ionization-mass spectrometry (ESI-MS) and further confirmed by x-ray diffractions. The possible mechanisms for the formation of 1 and 2 were also proposed.