USE OF SAMARIUM DIIODIDE AS AN ALTERNATIVE TO SODIUM MERCURY AMALGAM IN THE JULIA-LYTHGOE OLEFINATION

Studies into the use of samarium diiodide (SmI2) in the reductive elimination of 1,2-acetoxy sulfones and the reductive cleavage of vinyl sulfones are reported. Parallel investigations with sodium/mercury amalgam (Na/Hg) revealed over-reduction in several cases in which the desired products were heavily conjugated or conjugated to an aromatic moiety. A mechanistic study revealed some of the intricacies of the SmI2-promoted Julia-Lythgoe olefination. The classical Na/Hg reductive method was also examined, and an alternative mechanism is proposed. Observations described herein provide important insights into the mechanism and synthetic utility of these methods. The optimum protocol developed utilizes SmI2 reduction of vinyl sulfones in the presence of DMPU and MeOH and gives generally high yields with good to excellent E stereoselectivity.