Allylic sulfones containing triene moieties as key synthons for carotenoid synthesis

An efficient synthetic method for the allylic sulfone 2 containing a conjugated triene moiety has been proposed involving i) coupling of allylic sulfones 4 with the C-5 bromoallylic sulfide 5, ii) base-promoted dehydrosulfonation in the presence of allylic sulfide, and iii) selective oxidation of the resulting trienyl sulfide to the corresponding sulfone. Total synthesis of lycopene starting from the C-15 allylic sulfone 2b has been described, where the new C-10 bis(chloroallylic) sulfone 11 proved to be a useful substitute for the C-10 bis(chloroallylic) sulfide 3, which did not require the problematic chemoselective sulfur oxidation in a conjugated polyene.