Hydrogenation of Dewar‐benzene derivatives. II. Heterogeneous and homogeneous hydrogenation of dimethyl tetramethylbicyclo [2.2.0]hexa‐2,5‐diene‐2,3‐dicarboxylate and related compounds

Dimethyl tetramethylbicyclo[2.2.0]hexa‐2,5‐diene‐2,3‐dicarboxylate (1) and some related compounds were hydrogenated in the presence of a number of Group VIII metal catalysts. Heterogeneous hydrogenation under ambient conditions resulted in exo,exo addition of one mole of hydrogen. The regioselectivity was strongly dependent on the catalyst, and on the nature and steric requirements of the substituents. Hydrogenation of 1 in the presence of a homogeneous platinum‐tin catalyst resulted in exclusive hydrogenation of the ester‐substituted double bond; exo,endo hydrogenation was involved for 16%.