Syntheses of carotenoids involving the ylidenebutenolide structure.

In our previous papers (1, 2), we reported the synthesis of retinoidal 4 ylidenebutenolide (Scheme 1), the method of which involves Wittig reaction of the unstable conjugated anhydride (1) with the acetyl phosphorane (2). Attempts to extend the conjugation by use of the retinoidal 4-ylidenebutenolide (3) or (4) were unfortunately frustrated by the instability of intermediates. In addition, the ketone in (3) was unreactive to the conjugated polyene ylide. Therefore, the development of an alternative route is required for the total synthesis of peridinin (5) (3, 4) the unique C37-skeletal carotenoid pigment, which is contained in the planktonic algae, Dinofiagellates causing "red tide" and functions as an auxiliary light harvesting pig ment for photosynthesis (5).