Diels–Alder reactions of hexachlorocyclopentadiene led to the formation of the adducts I from nitroethylene, VI after hydrolysis of the adduct from itaconic anhydride, and X from dimethyl acetylenedicarboxylate. The nitro adduct I was converted to a sodium salt II which yielded the chloro (IVa) and bromo (IVb) derivatives on halogenation. The failure of II to undergo the Nef or related solvolysis reactions is attributed in part to an inductive effect of the chlorine substituents, since the corresponding acid III was shown to be 63 times as strong as the unchlorinated acid. Chemical reduction of I yielded the corresponding amine V. The diacid VI yielded, besides the anhydride VII, a monomethyl ester (VIII) and, under conditions which overcame the much greater steric hindrance of the second carboxyl, the dimethyl ester IX. Saponification of X yielded the diacid XI, which has properties different from a diacid described in the literature to which the same structure previously had been assigned.