Catalysis of the reaction: 2-hydroxychromene-2-carboxylate = (3E)-4-(2-hydroxyphenyl)-2-oxobut-3-enoate. (3E)-4-(2-hydroxyphenyl)-2-oxobut-3-enoate is also known as trans-o-hydroxybenzylidenepyruvate.
2-hydroxychromene-2-carboxylate isomerase activity