Diels-Alder reactions of lignin-derived quinones

The Diels-Alder reactions of methoxy- p -benzoquinone and 2,6-dimethoxy- p -benzoquinone, which may be obtained from lignin and lignin model compounds, and of o -quinones (4-methyl, 4-acetyl, and 4-(l-hydroxyethyl)- o -benzoquinone) were investigated using 2,3-dimethylbutadiene, isoprene and styrene as dienes. Dimethylbutadiene and isoprene were found to be effective reactants, resulting in the generation of several Diels-Alder addition products. Loss of the methoxyl group and the side chain were observed under certain conditions. Reactions of the p -benzoquinones went more smoothly than the reactions of the o -quinones, and product yields were generally higher. Higher yields of anthraquinone products were obtained from 2,6-dimethoxy- p -benzoquinone than from methoxy- p -benzoquinone.