disproportionation of dihydroquinoxalines for the synthesis of chiral tetrahydroquinoxalines using a metal/Brønstedacidrelaycatalysissystem has been developed. The use of hydrogen gas as the reductant makes the convergent disproportionation an ideal atom-economical process. A dramatic reversal of enantioselectivity was observed in the reduction of quinoxalines because of the different steric demands in
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
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。
A novel Ir-catalyzed asymmetric hydrogenation protocol for the synthesis of chiral tetrahydroquinoxaline (THQ) derivatives has been developed. By simply adjusting the reaction solvent, bothenantiomers of mono-substituted chiral THQs could be selectively obtained in high yields with excellent enantioselectivities (toluene/dioxane: up to 93% yield and 98% ee (R); EtOH: up to 83% yield and 93% ee (S))
开发了一种用于合成手性四氢喹喔啉 (THQ) 衍生物的新型 Ir 催化不对称氢化方案。通过简单地调整反应溶剂,即可高产率地选择性地获得单取代手性 THQ 的两种对映体,且具有优异的对映选择性(甲苯/二恶烷:收率高达 93%,ee ( R ) 高达 98%;EtOH:收率高达 83%)和 93% ee ( S ))。对于2,3-二取代的手性THQ,获得的顺式氢化产物的收率高达95%,dr为20:1,ee为94%。值得注意的是,该方法也适用于连续流动条件下,产生具有相当收率和对映选择性的克级产品(二恶烷:91% 收率和 93% ee ( R );EtOH:90% 收率和 87% ee ( S ))。与之前报道的 Ir 催化不对称氢化方案不同,该系统表现出显着的改进,因为它不需要额外的添加剂。此外,还进行了全面的机理研究,包括氘标记实验、对照实验、动力学研究和密度泛函理论(DFT)计算,以揭示两种对映体对映选择性的潜在机制。
Dihydrophenanthridine: A New and Easily Regenerable NAD(P)H Model for Biomimetic Asymmetric Hydrogenation
A new and easily regenerable NAD(P)H model 9,10-dihydrophenanthridine (DHPD) has been designed for biomimetic asymmetric hydrogenation of imines and aromatic compounds. This reaction features the use of hydrogen gas as terminal reductant for the regeneration of the DHPD under the mild condition. Therefore, the substrate scope is not limited in benzoxazinones; the biomimetic asymmetric hydrogenation of benzoxazines, quinoxafines, and quinolines also gives excellent activities and enantioselectivities. Meanwhile, an unexpected reversal of enantioselectivity was observed between the reactions promoted by the different NAD(P)H models, which is ascribed to the different hydride transfer pathway.