摘要/Abstract

手性吡咯烷骨架是合成具有生物活性的化合物、天然产物、药物和催化剂的重要中间体，其高效的不对称合成方法是有机化学研究热点之一.该工作通过一类新型的Ming-Phos手性配体实现了铜催化的亚甲胺叶立德与硝基烯烃的不对称[3+2]环加成反应，以较好的非对映选择性和对映选择性合成了一系列手性吡咯烷类化合物（ee值高达98%，产率高达95%）.该方法具有反应条件温和、操作简单、底物普适性广以及配体合成简单易制备等众多优点.
关键词: 铜催化, 膦配体, 环加成, 对映选择性, 叶立德
Optically pure pyrrolidine ring systems are core structural motifs found in a range of bioactive compounds, natural products, pharmaceuticals and catalysts. The synthesis of optically pure pyrrolidine ring systems is no longer mysterious as a great number of studies concerning the catalytic asymmetric 1,3-dipolar cycloaddition of iminoesters have been reported. Overall, the transition-metal-catalyzed asymmetric 1,3-dipolar cycloaddition of iminoesters with electron-deficient alkenes is one of the most powerful and straightforward synthetic tools for the optically pure pyrrolidines. However, high diastereo-and enantioselectivities are requested simultaneously during the synthesis of chiral substituted pyrrolidine and it still remains a big challenge to develop an efficient way to achieve both of them. Recently, we developed a novel chiral sulfinamide mono-phosphine (Ming-Phos) which performed well in copper-catalyzed intermolecular cycloaddition of iminoesters with β-trifluoromethyl β,β-disubstituted enones or α-trifluoromethyl α,β-unsaturated esters. Encouraged by the satisfying results, herein we report the Ming-Phos/Cu-catalyzed asymmetric intermolecular[3+2] cycloaddition of azomethine ylides with nitroalkenes. To our delight, a new Ming-Phos M3 bearing a trifluoromethyl showed good performance in this type of inter-molecular cycloaddition with high diastereo-and enantioselectivities (up to 13:1 dr, 98% ee and 95% yield). High efficiency, high diastereo-and enantioselectivity, a novel ligand, an inexpensive copper catalyst, and good functional group tolerance make it worth to be considered as an efficient, reliable and atom-economic strategy for the synthesis of optically pyrrolidines. The general procedure is as following:the solution of M3 (5.5 mol%) and Cu(CH₃CN)₄BF₄ (5 mol%) in methyl tert-butyl ether (MTBE, 6 mL) was stirred at room temperature for 2 h. After the reaction temperature was dropped to -30℃, azomethine ylides 2 (0.6 mmol), Cs₂CO₃ (0.15 mmol) and nitroalkene 1 (0.3 mmol) were added sequentially. After the nitroalkene 1 was consumed completely, the solvent was removed under reduced pressure. The crude product was analyzed with ¹H NMR to determine the diastereomeric ratio. Then the crude product was then purified by flash column chromatography on silica gel to afford the desired product.
Key words: copper catalysis, phosphine ligand, cycloaddition, enantioselectivity, ylides


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