General and systematic synthetic entry to carotenoid natural products

A general synthetic method of carotenoid natural products has been developed, in which the systematic chain extension and termination processes were applied. The syntheses of the chain extension and termination units were greatly improved by the use of the common intermediate, 1-bromo-4-chloro-3-methyl-2-butene (), in a short and highly efficient way. The C10 chain initiation β-cyclogeranyl sulfone () was coupled with the C5 chain extension unit to give the C15 chain-extended allylic sulfone after chemoselective sulfide oxidation. This chain-extended C15 allylic sulfone underwent the Julia olefination reaction with the C5 and the C10 chain termination units to give retinol () and β-carotene (), respectively.