Abstract

A pair of ortho-benzoate esters containing epimeric pyrroloimidazolones undergo sequential Birch reduction and diastereoselective alkylation to provide products ranging from 88:12 to >95:5 diastereomeric ratio (dr) for the syn-epimer, and 50:50 to 95:5 dr for the anti-epimer. The stereochemistry of the products is confirmed by a combination of X-ray crystallography on a key anti-epimer-derived product, in combination with specific rotation measurements of enantiomers that are prepared from the syn or anti starting materials. A diastereomerically pure allyl-substituted substrate is shown to undergo Cope rearrangement, which transposes the quaternary chiral center to a remote position without racemization. This work is complementary to asymmetric reductive alkylation reported previously by Schultz using anisole substrates with chiral benzamide auxiliaries in that the pyrroloimidazolones act as surrogates for the methoxy group.

中文翻译：

---

非对映异构合成吡咯烷基咪唑酮的烷基化1，4-环己二烯酯

摘要

一对含有对映体吡咯并咪唑酮的原苯甲酸酯进行连续的Birch还原和非对映选择性烷基化，以提供范围为88:12至> 95：5的顺式异构体非对映体比率（dr）和50:50至95：5 dr的产物为反epimer。通过对关键的抗表观异构体来源的产品进行X射线晶体学分析，并结合由顺式或反式制备的对映体的比旋光度，可以确定产品的立体化学起始材料。非对映体纯的烯丙基取代的底物显示出发生Cope重排，该重排将四价手性中心转位至较远的位置而没有消旋作用。这项工作是舒尔茨先前报道的使用具有手性苯甲酰胺助剂的茴香醚底物的不对称还原烷基化的补充，因为吡咯并咪唑酮可作为甲氧基的替代物。