ASYMMETRIC OXIDATION OF SIMPLE SELENIDES TO SELENOXIDES IN HIGH ENANTIOPURITY - STEREOCHEMICAL ASPECTS OF THE ALLYL SELENOXIDE ALLYL SELENENATE REARRANGEMENT

For the first time simple alkyl aryl selenoxides of high enantiomeric purity (90-95% ee) and well-defined stereochemistry are available via the asymmetric oxidation of selenides using (+)- or (-)-N-(phenylsulfonyl)-(3,3-dichlorocamphoryl)oxaziridine [4, [3,3-dichloro-1,7,7-trimethyl-2'-(phenylsulfonyl)spiro[bicyclo[2.2.1]heptane-2,3'-oxaziridine]]]. These nonracemic selenoxides, which are more stable in solution than in the solid state, exhibit high configurational stability as long as acid and moisture are excluded. Complete racemization occurs within minutes on addition of trace amounts of acid and water. The asymmetric oxidation of (E)- and (Z)-aryl cinnamyl selenides 11 and 12 with oxaziridine (+)-4 affords optically active 1-phenyl allyl alcohol (15) via a concerted [2,3] sigmatropic selenoxide-selenenate rearrangement. The extent of 1 --> 3 chirality transfer (41-62% ee) as well as the endo/exo transition state geometry is highly dependent on the structure of the allylic selenide.