Asymmetric N1 Unit Transfer to Olefins with a Chiral Nitridomanganese Complex:  Novel Stereoselective Pathways to Aziridines or Oxazolines

Chiral nitridomanganese complex 1 was found to be a highly potential N1 unit source for the asymmetric synthesis of aziridines and 2-oxazolines from olefins such as styrene and its derivatives. When sulfonyl chlorides were employed as activators of the complex in the presence of pyridine, pyridine N-oxide, and a silver salt, the reaction of olefins with complex 1 proceeded smoothly to afford the N-sulfonylated aziridines. The aziridination of styrene derivatives with complex 1 using 2-trimethylsilylethanesulfonyl chloride (SESCl) gave the N-SES-aziridines, which were easily converted into chiral N-unsubstituted aziridines. It was found that the reaction was applicable to the asymmetric synthesis of 2-oxazolines from olefins when acyl chlorides were employed as activators. Complex 1 provided an effective asymmetric environment for trans-disubstituted styrenes in the reaction (up to 92% ee). This is the first example of a direct asymmetric synthesis of 2-oxazolines from olefins. Additional experiments, conducted during the course of this investigation, suggest that the isomerization of the N-acylaziridine intermediate is involved in this reaction.