Reactivity increase of dienophiles by change of the ester substituents into the acid chlorides: cycloaddition reaction of the diacid chloride of 3,10-hexacyclo[10.2.1.15,8.02,11.03,10.04,9]hexadeca-6,13-diene-3,10-dicarboxylic acid with quadricyclane

Conversion of the ester substituents on the cyclobutene π-bond of dimethyl tricyclo[4.2.1.02,5]nona-3,7-diene-3,4-dicarboxylate to the corresponding acid chloride increases the cycloaddition reactivity toward quadricyclane so dramatically that the reaction temperature can be dropped from 180 °C (preparation of title 3,10-diester) to room temperature (preparation of the title 3,10-diacid chloride). The cycloadduct product, an acid chloride of the title ring system, is extremely docile and can be recrystallized unchanged from hot methanol.