Asymmetric imidation of organic selenides into selenimides

Treatment of aryl benzyl selenides with [N-(p-toluenesulfonyl)imino]phenyliodinane [TsNIPh] in the absence or presence of copper(I) salt in toluene or acetonitrile affords the corresponding N-tosylselenimides in 31–46% yield. When the reaction is carried out in the presence of optically active 4,4′-disubstituted bis(oxazoline) as a ligand together with molecular sieves, enantioselective imidation occurs to give optically active N-tosylselenimides and the best result is obtained from benzyl 2-naphthyl selenide (64% yield and 36% ee). Similar treatment of allylic selenides gives the corresponding optically active allylic amides (up to 71% yield and 30% ee). In the case of diastereoselective imidation, the reaction of diaryl selenides bearing a chiral oxazolinyl moiety with TsNIPh or Chloramine–T trihydrate [TsN(Cl)Na·3H2O] has been successfully carried out to give the corresponding optically active N-tosylselenimides in good yields (up to 97% isolated yield and 76% de). The absolute configuration around the selenium atom of (4S)-Se-[2-(4-isopropyloxazolin-2-yl)phenyl]-Se-phenyl-N-(p-toluenesulfonyl)selenimide [(4S)-13], obtained by diastereoselective imidation of the corresponding selenide with Chloramine–T trihydrate, has been determined to be S by X-ray crystallographic analysis, from the result of which an ionic reaction pathway involving a chloroselenonium ion intermediate is proposed.