Synthesis of C40‐Symmetrical Fully Conjugated Carotenoids by Olefin Metathesis

In an effort to push olefin metathesis to the limits of conjugation in reactants and products, the C40‐symmetrical carotenoids β,β‐carotene (1), lycopene (2), (3R,3′R)‐zeaxanthin (3), and rac‐isozeaxanthin (4), which are conjugated undecaenes, have been synthesized from C21‐terminal hexaenes by treatment with Grubbs' second‐generation Ru catalyst in dichloromethane at 50 °C.