Isomerization of the cis, trans isomers of 1,2,5,6-tetrasubstituted-1,5-cyclooctadienes to the corresponding cis, cis-isomers

A process for the production of a 1,2,5,6-tetrasubstituted-cis,cis-1,5-cyclooctadiene of the formula ##STR2## wherein each Q is individually selected from the group consisting of --CN, --COOH, --CONH.sub.2, --COX and --COOR, wherein R is an alkyl group having from 1 to 4 carbon atoms and X is selected from the group consisting of Cl and Br, which comprises isomerizing the corresponding 1,2,5,6-tetrasubstituted-cis,trans-1,5-cyclooctadiene in the presence of an isomerization promoting amount of a halogen promoter selected from the group consisting of chlorine, bromine and iodine, at a temperature in the range of -50.degree. to 100.degree. C, for a time sufficient to effect said isomerization, in the absence of light.