The first B(C6F5)3‐catalyzed deoxygenative reduction of amides into the corresponding amines with readily accessible and stable ammonia borane (AB) as a reducing agent under mild reaction conditions is reported. This metal‐free protocol provides facile access to a wide range of structurally diverse amine products in good to excellent yields, and various functional groups including those that are reduction‐sensitive
据报道,在温和的反应条件下,用易于获得且稳定的氨硼烷(AB)作为还原剂,将酰胺进行的首次B(C 6 F 5)3催化脱氧还原为相应的胺。该无金属方案可轻松获得各种结构多样的胺产品,且收率高至优异,并且对各种官能团(包括对还原敏感的官能团)均具有良好的耐受性。该新方法也适用于手性酰胺底物,而不会破坏对映体的纯度。BF 3 OEt 2助催化剂在该反应中的作用是通过酰胺-硼加合物的原位形成来活化酰胺羰基。
The First General, Efficient and Highly Enantioselective Reduction of Quinoxalines and Quinoxalinones
作者:Magnus Rueping、Francisco Tato、Fenja. R. Schoepke
DOI:10.1002/chem.200902907
日期:——
Simple yet efficient: A series of diverse substituted tetrahydroquinoxalines and dihydroquinoxalinones have been synthesized for the first time in a highly enantioselective fashion (see scheme). Using this metal‐free hydrogenation it is possible to isolate these products, which are of high pharmaceutical interest, in good yields and with excellent enantioselectivities in a minimal number of reaction
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
Exploration of chiral diastereomeric spiroketal (SPIROL)-based phosphinite ligands in asymmetric hydrogenation of heterocycles
作者:Siyuan Sun、Pavel Nagorny
DOI:10.1039/d0cc03088k
日期:——
best ligands for these transformations, the (S,R,R)-diastereomer of SPIRAPO was found to be highly effective ligand for the reduction of 20 different heterocyclic systems with loadings as low as S/C = 10 000. This dearomatizative hydrogenation provided direct access to optically active tetrahydroquinolines in high enantioselectivities (up to 94% ee) and excellent yields (up to 99%), and was used to
已经制备了新的和容易获得的基于手性SPIROL的二亚膦酸酯配体(SPIRAPO),并将其用于铱催化的喹啉,喹喔啉和2 H -1,4-bezoxazin-2-ones的不对称氢化。虽然结构相似的(R,R,R)-SPIRAPO和(R)-SPINOL基亚膦酸酯不是这些转化的最佳配体,但(S,R,R发现SPIRAPO的)-非对映异构体是还原20个不同S / C = 10000负载的不同杂环系统的高效配体。这种脱芳香化氢化反应可直接获得高对映选择性(高达94%的光学活性四氢喹啉) ee)和极佳的收率(高达99%),并用于生成1.75 g天然生物碱(-)-(R)-鸟苷。该方案随后被扩展以实现喹喔啉和2 H -1,4-苯并恶嗪-2-酮的不对称氢化,具有良好至优异的对映选择性。
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。