General and systematic synthetic entry to carotenoid natural products

Functions, Therapeutic Applications, and Synthesis of Retinoids and Carotenoids

“…Wittig reactions and sulfone chemistry have been combined using as a common building block the C 20 phosphonium salt derived from retinol (see 658 , Scheme ) and C 20 aldehydes containing chloroallyl-, acetalalkyl- (X), and alkenyl-sulfone groups, followed by double elimination processes induced by treatment of 655 and 656 with KOH or KOMe . Other versions of the double sulfone alkylation/elimination approach to symmetrical carotenoids developed included as intermediates bis-allylsulfones 651 and 654 and a bis-alkyl, bis-vinyltetrasulfone 650 . These intermediates were instead obtained by Ramberg–Bäcklund rearrangement of the precursors with an additional central bis-allylsulfone substructure obtained by alkylation of sulfones 184 (Scheme ) and 198 (Scheme ).…”