The catalytic transfer hydrogenation (CTH) of dimethyl bicyclo [2.2. l] hepta-2, 5-diene-2, 3- dicarboxylate (3) on palladium on carbon is highly regioselective, giving predominant reduction at the least-substituted olefinic site. The CTH of dimethyl bicyclo [2.2. 1] hept-2-ene- 2, 3-dicarboxylate also occurs with exclusive suprafacial exo addition of hydrogen to afford the endo isomer. An increase in the relative concentration of palladium on carbon (ca. 40- ...