71. 3-Triethylsilyloxypentadienyllithium, a Versatile 1,3-Diene- or Vinyl Ketone-Building Block
    Oppolzer, W.; Snowden, R. L.; Simmons, D. P.
    Helv. Chim. Acta 1981, 64, 2002-2021

Deprotonation of the 3-trialkylsilyloxy-1,4-diene 3a and subsequent electrophilic substitution of the non-isolated 3-trialkylsilyoxypentadienyllithium 4 gives the α- and γ-products 8 and/or 6 in good yields. Whereas alkylation of 4 proceeds with variable regioselectivity (Table 1) aldehydes and ketones attack preferentially the γ-position of 4(Table 2). The desired γ-products 6 may be directly subjected to inter- and intramolecular [4 + 2]-additions as demonstrated by the reactions 5a (Ξ6d) → 7 and 6h → 19(Schemes 4 and12). Alternatively, smooth fluoride-promoted silylether-cleavage 6 → 11(Scheme 8) provides a convenient approach to substituted vinyl ketones such as to the natural products 11f(Table 3). The stereoselective conversion 6k → 23(Scheme 13) implies an endo-selective intramolecular Diels-Alder addition (26 → 23) and exemplifies the use of 4 as an equivalent of the hypothetical anion IV. Furthermore, some electrophilic substitutions of the hexadienyllithium 15 have been studied (Scheme 10).

DOI : 10.1002/hlca.19810640705