A Highly Efficient Chain-Extension Process in the Systematic Syntheses of Carotenoid Natural Products This work was supported by the RRC program of MOST and KOSEF.

Successive elongation by a C5 unit is possible when an allylic sulfone is coupled with 4-bromo-3-methyl-2-butenyl phenyl sulfide (1). The thiosulfone compound formed was then oxidized to the corresponding disulfone, which, upon coupling with another equivalent of 1 and oxidation, produced the trisulfone 2, again elongated by a C5 unit (see scheme). This process, which can be repeated again, is the basis for a highly efficient synthesis of carotenoids.