Scheme 1.
Equilibria between DB-67 lactone (I), DB-67 carboxylic acid (II) and the DB-67 carboxylate monoanion (III) and dianion (IV).
Equilibria between DB-67 lactone (I), DB-67 carboxylic acid (II) and the DB-67 carboxylate monoanion (III) and dianion (IV).