SYNTHESIS OF [R,S-R,S]-BIS[2-[1-(DIMETHYLAMINO)ETHYL]FERROCENYL]DISELENIDES AND [S,R-S,R]-BIS[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] diselenides ([R,S;R,S] and [S,R;S,R]), each of which possesses two axial and two central elements of chirality, have been prepared by lithiation of commercially available chiral [1-(dimethylamino)ethyl]ferrocenes, followed by reaction with elemental selenium and air oxidation, in 77-80% isolated yields. The structure of the [S,R;S,R]-bisferrocenyl diselenide has been fully characterized by X-ray crystallography. Six chiral ferrocenyl vinylic selenides and six chiral allylic ferrocenyl selenides have been newly prepared by reaction of the diselenides with the corresponding propiolate derivatives and allylic halides. The oxidation of the vinylic selenides with m-chloroperbenzoic acid in various organic solvents produces axially chiral allenecarboxylic esters via asymmetric selenoxide elimination in 27-59% chemical yields with high enantioselectivities (up to 89% ee). Similar treatment of the allylic selenides afforded the corresponding chiral allylic alcohols via asymmetric [2,3]sigmatropic rearrangement in 28-82% chemical yields with high enantioselectivities (up to 89% ee). The observed high enantioselectivities indicate that oxidation proceeds highly diastereoselectively, that the resultant chiral selenoxides are slow to racemize, and also that selenoxide elimination and [2,3]sigmatropic rearrangement proceed with little loss of optical activity.