Cross metathesis of β-carotene with electron-deficient dienes. A direct route to retinoids

Cross metathesis (CM) reactions of β-carotene and alkenes occur regioselectively in the presence of the Hoveyda second generation catalyst. Scission of the C15-C15′ and C11-C12 bonds of β-carotene in all CM reactions predominates. The reaction with ethyl (2E,4E/Z)-3-methylhexa-2,4-dienoate is both regio- and diastereoselective, and affords ethyl all-trans-retinoate as the major product, if suitable CM conditions are applied.