together! A selective Fe‐catalysed enantioselective reduction of quinoxalines and benzoxazines with hydrogen is demonstrated. Key to success is the combination of a chiral Brønsted acid and a well‐defined non‐chiral Fe hydrogenation catalyst. This methodology constitutes an attractive and environmentally favourable alternative to well‐established asymmetric hydrogenations by using precious‐metal‐based catalysts
chiral Ir/H8‐binapo catalyst exhibits unprecedented reactivity and excellent enantioselectivity in the hydrogenation of quinoxalines at a high ratio of substrate to catalyst (from 100 to 20 000). This new method provides a practical synthetic approach to give optically active chiral tetrahydroquinoxaline derivatives (see scheme; cod=1,5‐cyclooctadiene).
在底物与催化剂的高比例(100至20000)下,一种容易获得的手性Ir / H 8联苯胺催化剂在喹喔啉加氢中表现出空前的反应性和出色的对映选择性。这种新方法提供了一种实用的合成方法,可以得到光学活性的手性四氢喹喔啉衍生物(参见方案; cod = 1,5-环辛二烯)。
General Asymmetric Hydrogenation of 2-Alkyl- and 2-Aryl-Substituted Quinoxaline Derivatives Catalyzed by Iridium-Difluorphos: Unusual Halide Effect and Synthetic Application
A general asymmetric hydrogenation of a wide range of 2-alkyl- and 2-aryl-substituted quinoxaline derivatives catalyzed by an iridium–difluorphos complex has been developed. Under mild reaction conditions, the corresponding biologically relevant 2-substituted-1,2,3,4-tetrahydroquinoxaline units were obtained in high yields and good to excellent enantioselectivities up to 95%. With a catalyst ratio
已开发出由铱-二氟配合物催化的各种2-烷基和2-芳基取代的喹喔啉衍生物的一般不对称氢化反应。在温和的反应条件下,可以以高收率和高达95%的良好至优异的对映选择性获得相应的生物学上相关的2-取代-1,2,3,4-四氢喹喔啉单元。催化剂比为S / C = 1000且以克为单位,Ir-二氟膦配合物的催化活性得以保持,并显示出其潜在价值。最后,我们证明了我们的方法在化合物(S)-9的合成中的应用,该化合物是胆固醇酯转移蛋白(CETP)的抑制剂。
Iridium‐Difluorphos‐Catalyzed Asymmetric Hydrogenation of 2‐Alkyl‐ and 2‐Aryl‐Substituted Quinoxalines: A General and Efficient Route into Tetrahydroquinoxalines
AbstractA highly efficient and general iridium‐difluorphos‐catalyzed asymmetric hydrogenation of diverse 2‐alkyl‐ and 2‐aryl‐substituted quinoxalines into biologically and pharmaceutically relevant 2‐substituted‐1,2,3,4‐tetrahydroquinoxaline units has been developed. High isolated yields and excellent enantioselectivities of up to 95% for 2‐alkyl‐substituted quinoxalines and of up to 94% for 2‐aryl‐substituted quinoxalines were obtained.