Conversion of a catechol into a but-2-enolide

Reactions of 6,7,8,9-tetrahydro-5H-benzocycloheptene-2,3-diol with alkaline oxidising agents gives 2-carboxymethylcycloheptanone, which easily forms the corresponding lactone. An o-quinone is demonstrated to be an intermediate. Several other mono- and bi-cyclic o-quinones examined do not undergo this type of reaction.