Trinity Biomedical Sciences Institute, School of Chemistry, The University of Dublin, Trinity College, Dublin 2, Ireland.
Org Biomol Chem. 2013 Jun 7;11(21):3535-40. doi: 10.1039/c3ob27271k. Epub 2013 Apr 18.
A new ylide-based protocol for the asymmetric aziridination of imines via methylene transfer has been developed involving the use of a simple chiral sulfonium salt and an organic strong base. A systematic study identified triisopropylphenyl sulfonylimines as optimal substrates for the process. Unexpectedly, hindered C2-symmetric sulfonyl salts incorporating bulky ethers at C-2 and C-5--which had previously been useful in the corresponding epoxidation chemistry--decomposed in these aziridination reactions via competing elimination pathways. Under optimised conditions it was found that a simple salt derived from (2R,5R)-2,5-diisopropyl thiolane could mediate asymmetric methylene transfer to a range of imines with uniformly excellent yields with 19-30% ee. Since this is a similar level of enantiomeric excess to that obtained using these same salts in epoxidation chemistry, it was concluded that if more bulky sulfonium salts could be devised which were resistant to decomposition under the reaction conditions, that highly enantioselective aziridine formation by methylene transfer would be possible.
一种新的基于叶立德的亚胺不对称氮丙啶化方法通过亚甲基转移得到了发展，涉及使用简单的手性锍盐和有机强碱。系统研究确定三异丙基苯基磺酰亚胺是该过程的最佳底物。出乎意料的是，在相应的环氧化反应中曾经有用的在 C-2 和 C-5 位具有大醚基的位阻 C2-对称磺酰盐通过竞争消除途径在这些氮丙啶化反应中分解。在优化条件下，发现由（2R，5R）-2,5-二异丙基硫醇衍生的简单盐可以将不对称亚甲基转移到一系列亚胺上，产率均匀，ee 值为 19-30%。由于这与使用相同盐在环氧化反应中获得的对映体过量相当，因此得出结论，如果可以设计出更位阻的锍盐，它们能够在反应条件下抵抗分解，那么通过亚甲基转移形成高对映选择性氮丙啶是可能的。
