3-Triethylsilyloxypentadienyllithium, a Versatile 1,3-Diene- or Vinyl ketone-Building Block

Article abstract of DOI:10.1002/hlca.19810640705

Deprotonation of the 3-trialkylsilyloxy-1,4-diene 3a and subsequent electrophilic substitution of the non-isolated 3-trialkylsilyloxypentadienyllithium 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(=6d)-->7 and 6h-->19 (schemes 4 and 12).Alternatively, smooth fluoride-promoted silylether-cleavage 6-->11 (Scheme 8) provides a convenient approach to substituted vinyl ketones such as to the natural product 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).