SYNTHESIS OF S[2-[1-(DIMETHYLAMINO)ETHYL]FERROCENYL]DISELENIDES AND S[2-[1-(DIMETHYLAMINO)ETHYL]FERROCENYL]DISELENIDES AND THEIR APPLICATION TO ASYMMETRIC SELENOXIDE ELIMINATION AND [2,3]SIGMATROPIC REARRANGEMENT

Novel optically-active bis[2-[1-(dimethylamino)ethyl]ferrocenyl] disel enides ([R,S;R,S] and [S,R;S,R]), each of which possesses two axial an d two central elements of chirality, have been prepared by lithiation of commercially available chiral [1-(dimethylamino)ethyl]ferrocenes, f ollowed by reaction with elemental selenium and air oxidation, in 77-8 0% isolated yields. The structure of the [S,R;S,R]-bisferrocenyl disel enide has been fully characterized by X-ray crystallography. Six chira l ferrocenyl vinylic selenides and six chiral allylic ferrocenyl selen ides have been newly prepared by reaction of the diselenides with the corresponding propiolate derivatives and allylic halides. The oxidatio n of the vinylic selenides with m-chloroperbenzoic acid in various org anic solvents produces axially chiral allenecarboxylic esters via asym metric selenoxide elimination in 27-59% chemical yields with high enan tioselectivities (up to 89% ee). Similar treatment of the allylic sele nides afforded the corresponding chiral allylic alcohols via asymmetri c [2,3]sigmatropic rearrangement in 28-82% chemical yields with high e nantioselectivities (up to 89% ee). The observed high enantioselectivi ties indicate that oxidation proceeds highly diastereoselectively, tha t the resultant chiral selenoxides are slow to racemize, and also that selenoxide elimination and [2,3]sigmatropic rearrangement proceed wit h little loss of optical activity.