| Organoselenium chemistry is a powerful tool for the synthetic chemist, and a number of versatile selenium reagents have been developed for the introduction of selenium into organic molecules. Since these reactions are often accompanied by the generation of new stereocentres, the extension of this chemistry to the asymmetric realm has recently received much attention. This Dissertation describes the preparation of several novel chiral auxiliaries for selenium, as well as some asymmetric reactions of these species. It also relates the unexpected formation of some selenium heterocycles which was fortuitously observed during this work.;Attempts to study nicotineseleno species was thwarted by difficulties in their preparation.;The reaction of camphor enolate with selenium, followed by aerial oxidation provided di(endo-3-camphoryl) diselenide in good yield. Modification of the C(2)-carbonyl group of the camphor moiety generated a series of seven chiral diselenides. Epoxide openings, hydroxyselenenylations, and (2,3) sigmatropic rearrangements mediated by the novel chiral auxiliaries proceeded in good yield but with poor stereoselectivity. However, N,O-carbonyl-endo-2-aminomethylene-exo-2-hydroxy-endo-3-bornaneselenenyl chloride cyclized alkenols and alkenoic acids in high yield, with high stereoselectivity (up to 90% de).;When the reactive electrophile, N-acetyl-endo-2-aminomethylene-exo-2-hydroxy-endo-3-bornaneselenenyl trifluoromethanesulfonate was generated in situ, it cyclized to produce a stable selenenamide. The latter catalyzed the oxidation of ;Reaction of camphor enolate with selenium in the presence of methyl iodide produced two isomeric dimers of 3-selenoxocamphor. An independent synthesis of the selenoketone by base-catalyzed elimination of hydrogen cyanide from 3-selenocyanatocamphor, followed by similar dimerization supports the intermediacy of this species. Similar elimination of hydrogen cyanide from 3-thiocyanatocamphor generated 3-thioxocamphor in situ, which dimerized to a unique 1,3-dithietane. Hydrolysis of 3-tellurocyanato-2-trimethylsilyloxy-2-bornene generated 3-telluroxocamphor in situ, which also dimerized to afford two isomeric 1,3-ditelluretanes. The structures of the dithietane and one diselenetane and ditelluretane were confirmed by X-ray crystallography. |
