Thomasidioic acid and 6-hydroxy-5,7-dimethoxy-2-naphthoic acid: Are they really natural products?

It has been shown that air oxidation of alkaline aqueous solutions of sinapic acid produces both thomasidioic acid (1), and 6-hydroxy-5,7-dimethoxy-2-naphthoic acid (2) in high yield, with the relative amounts dependent on the basicity of the solution. It has also been shown that naphthoic acid 2 is a secondary oxidation product of thomasidioic acid, a reaction that also produces 2,6-dimethoxy-p-benzoquione (3). The question of whether compounds 1, 2 and 3 are really natural products, as previously reported, is discussed. (C) 1997 Elsevier Science Ltd.