Conformationally constrained precursors to retinoic acid analogs which stabilize the 9Z-configuration

The iodine-catalyzed isomerization (dark) of (2Z,4E)-4-(2′-isopropylidenecyclohexylidene)-3-methyl-2,4-butadienal and (2Z,4E)-4-(2′-isopropyl-3′-methyl-2′-cyclohexen-1′-ylidene)-3-methyl-2-butenal, precursors to conformationally defined 6-s-cis and 6-s-trans retinoic acid analogs, resulted in the formation of isomer mixtures for which the 9Z-configuration [using retinoic acid numbering] is most stable.