Oxidative carbomethoxylation of cyclopentene (1) under carbon monoxide and air by the use of a catalytic amount of Pd(OAc)(2) and molybdovanadophosphate (NPMoV) led to dimethyl cis-1,2-cyclopentanedicarboxylate (2) and dimethyl cis-1,3-cyclopentanedicarboxylate (3) in good yields. Total yields of 2 and 3 were found to be improved by adding a small amount of NH4Cl. Several alkenes were similarly converted into the corresponding dimethyl dicarboxylates. The role of Cl- in the present catalytic system is suggested.
Sicher,J. et al., Collection of Czechoslovak Chemical Communications, 1961, vol. 26, p. 262 - 275