A New Route to Vitamin E Key-Intermediates by Olefin Cross-Metathesis

Ru‐Catalyzed olefin cross‐metathesis (CM) has been successfully applied to the synthesis of several phytyl derivatives (2b, 2d–f, 3b) with a trisubstituted CC bond, as useful intermediates for an alternative route to α‐tocopheryl acetate (vitamin E acetate; 1b) (Scheme 1). Using the second‐generation Grubbs catalyst RuCl2(C21H26N2)(CHPh)PCy3 (Cy = cyclohexyl; 4a) and Hoveyda–Grubbs catalyst RuCl2(C21H26N2){CH‐C6H4(O‐iPr)‐2} (4b), the reactions were performed with various C‐allyl (5a–f, 7a,b) and O‐allyl (8a–d) derivatives of trimethylhydroquinone‐1‐acetate as substrates. 2,6,10,14‐Tetramethylpentadec‐1‐ene (6a) and derivatives 6c–e of phytol (6b) as well as phytal (6f) were employed as olefin partners for the CM reactions (Schemes 2 and 5). The vitamin E precursors could be prepared in up to 83% isolated yield as (E/Z)‐mixtures.