ASYMMETRIC [2,3] SIGMATROPIC REARRANGEMENT VIA CHIRAL SELENOXIDE WITH SHARPLESS OXIDANTS

The Sharpless oxidation of some aryl cinnamyl selenides afforded a chiral 1-phenyl-2-propen-1-ol via asymmetric [2,3] sigmatropic rearrangement in a moderate to high enantiomeric excess (up to 92% e.e.). The enantioselectivity was found to be enhanced remarkably by the introduction of the o-nitro group to an arylseleno moiety of the substrate and the use of diisopropyl tartrate (DIPT) ligand in the Sharpless oxidant. In the rearrangement step two possible transition states (TS(exo) and TS(endo)) are conceivable in which TS(endo) was revealed to be more stable by 4.2 kcal/mol than TS(exo) from the extend-Huckel calculation.