General and systematic synthetic entry to carotenoid natural products

Abstract 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 ( 8 ), in a short and highly efficient way. The C 10 chain initiation β-cyclogeranyl sulfone ( 3 ) was coupled with the C 5 chain extension unit to give the C 15 chain-extended allylic sulfone after chemoselective sulfide oxidation. This chain-extended C 15 allylic sulfone underwent the Julia olefination reaction with the C 5 and the C 10 chain termination units to give retinol ( 1 ) and β-carotene ( 2 ), respectively.