多功能手性膦催化活泼烯烃的不对称分子间Rauhut-Currier反应

Highly Enantioselective Intermolecular Rauhut–Currier Reaction of Activated Alkenes Catalyzed by Multifunctional Chiral Phosphine

研究实现了多功能手性膦催化的3-芳酰基丙烯酸酯和烯酮的不对称分子间Rauhut-Currier反应,为多羰基手性化合物的构建提供了一种新方法.在使用(S,RS)-X8作为催化剂和甲苯作为溶剂的条件下,一系列含有不同取代基团的3-芳酰基丙烯酸酯和烯酮均可顺利地发生不对称Rauhut-Currier反应,从而高产率且高对映选择性地生成相应的产物.对照实验表明多功能手性膦催化剂中的N—H键对反应的对映选择性的控制起到了至关重要的作用;膦谱监测实验结果表明手性膦催化剂对烯酮的Michael加成是该反应的启动步骤.

The Rauhut-Currier （R-C） reaction, first disclosed by Rauhut and Currier in 1963, is an atom economy strategy for the construction of carbon-carbon bond and a wide range of synthetic valuable building blocks. During the past few decades, significant progress on the enantioselective intramolecular R-C reactions has been achieved by utilizing diverse chiral nucleophilic catalysts such as cysteine derivatives, L-prolinol, hydrogen-bonding catalyst and β-aminephosphine. However, compared to the well-developed enantioselective intramolecular R-C reactions, the enantioselective cross intermolecular R-C reaction concerning two different alkenes has been rarely explored so far. The enantioselective cross R-C reaction still suffers from a series of drawbacks such as low reactivity, enantioselectivity, limited substrate scope and higher catalyst loading. Thus, the development of novel chiral nucleophilic catalyst, for highly enantioselective cross R-C reaction is highly desirable. In this article, we wish to report the application of Xiao-Phos in the highly enantioselective cross intermolecular R-C reaction of vinyl ketone and activated alkenes. Accordingly, a stirred solution of 3-aroyl acrylates 1 （0.2 retool） and （S,Rs）-X8 （0.02 mmol） in toluene （2 mL） was cooled to -20 ℃. Subsequently, vinyl ketone 2 （0.4 mmol for aryl vinyl ketone and 0.6 mmol for alkyl vinyl ketone） was added in one portion through a syringe. The mixture was stirred at this temperature until completion of 3-aroyl acrylate as indicated by TLC. After completion of the reaction, the reaction mixture was directly purified by silica gel chromatography to afford the desired RC product. What＇s more, control experiments demonstrated that the presence of free sulfinamide N--H in Xiao-Phos is crucial for the enantioselective cross R-C reaction. Finally, for more details about （S,Rs）-X8 in the enantioselective cross R-C reaction, control experiments monitored by 31p NMR spectroscopy were conducted and the 31p NMR experiments indicated that this cross intermolecular R-C reaction was initiated by the Michael addition of （S,Rs）-X8 to vinyl ketone 2.