Maleic anhydride is the most widely used dienophile in Diels-Alder reactions as it reacts readily with a wide variety of dienes. However, if the synthesis of a new six-carbon ring without substituents is desired, one must either remove the adjacent carboxyl groups from the adduct or use a dienophile which has groups more readily removed than carboxyl. The former problem still awaits a good general solution.* We therefore thought of the latter ...
