Cycloaddition reactions of a lignin-derived pyrone derivative, 2-pyrone-4,6-dicarboxylic acid, and its dimethyl ester with alkenyl acetates and alkynes under thermal conditions proceed with decarboxylation to give isophthalic acids and various mono- and disubstituted isophthalates. A ruthenium complex catalyzes the reaction with alkynes under milder conditions and affords products with different regioselectivity from that observed under thermal conditions.