Department of Organic Chemistry, Institute of Chemistry, University of Pannonia, Post Office Box 158, H-8201 Veszprém, Hungary.
J Org Chem. 2011 Aug 5;76(15):6048-56. doi: 10.1021/jo2006285. Epub 2011 Jul 5.
Ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF(6)) and 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF(4)) were found to promote an unusual Wagner-Meerwein rearrangement of steroidal 16α,17α-epoxides leading to unnatural 13-epi-18-nor-16-one derivatives as the main products. These compounds were isolated in good to excellent yields. 16α-Hydroxy-Δ(13)-18-norsteroids, the results of the usual rearrangement, were obtained as minor components of the reaction mixtures. The ionic liquid bmimPF(6) was shown to induce C-ring aromatization of 16α,17α-epoxyestranes due to the formation of HF, the hydrolysis product of PF(6). Increasing amounts of HF and PO(2)F(2) were detected by (19)F and (31)P NMR when the ionic liquid was reused. The structures of the steroidal products, 16-oxo-18-nor-13α-steroid derivatives, 16α-hydroxy-Δ(13)-18-norsteroids, and C-aromatic compounds were determined by two-dimensional NMR techniques and high-resolution mass spectrometry (HRMS). The ionic liquids were recirculated efficiently.
离子液体 1-丁基-3-甲基咪唑六氟磷酸盐(bmimPF(6))和 1-丁基-3-甲基咪唑四氟硼酸盐(bmimBF(4))被发现能促进甾体 16α,17α-环氧化物的异常 Wagner-Meerwein 重排，生成非天然的 13-表-18-去甲-16-酮衍生物作为主要产物。这些化合物以良好到优异的产率被分离出来。16α-羟基-Δ(13)-18-去甲甾体是通常重排的结果，作为反应混合物的次要成分获得。离子液体bmimPF(6)被证明能诱导 16α,17α-环氧雌烷的 C 环芳构化，这是由于PF(6)的水解产物 HF 的形成。当离子液体被重复使用时，通过(19)F 和(31)P NMR 检测到 HF 和PO(2)F(2)的含量增加。甾体产物的结构，16-酮-18-去甲-13α-甾体衍生物、16α-羟基-Δ(13)-18-去甲甾体和 C-芳族化合物通过二维 NMR 技术和高分辨率质谱(HRMS)确定。离子液体被有效地循环使用。
