Efficient Synthesis of Maleimides and Carbazoles via Zn(OTf)2-Catalyzed Tandem Annulations of Isonitriles and Allenic Esters
摘要:
Lewis acid Zn(OTf)(2)-catalyzed tandem annulations of isonitriles and allenic esters which lead to efficient and flexible syntheses of a range of biologically significant maleimides and carbazoles and related compounds are reported. A mechanistic rationale is proposed to account for the observed reactivity.
Efficientborylation of sp3 C–O bonds by supported Au catalysts is described. Au nanoparticles supported on TiO2 showed high activity under mild conditions employing low catalyst loading conditions without the aid of any additives, such as phosphine and bases. A variety of allyl, propargyl, and benzyl substrates participated in the heterogeneously catalyzed reactions to furnish the corresponding allyl
描述了负载型Au催化剂对sp 3 C–O键的有效硼化作用。负载在TiO 2上的Au纳米颗粒在温和条件下采用低催化剂负载条件显示出高活性,而无需任何添加剂,例如膦和碱。各种烯丙基,炔丙基和苄基底物参与了非均相催化反应,以高产率提供了相应的烯丙基,烯丙基和苄基硼酸酯。此外,Au / TiO 2对烯丙基和苄基醇的直接硼化也有效。基于Hammett研究和控制实验的机理研究表明,负载型Au催化剂上的sp 3 C–O键硼化通过S N进行1'型机制涉及碳阳离子中间体的形成。负载的金催化剂的高活性,可重复使用性和环境相容性以及反应体系的可扩展性使有价值的有机硼化合物的实际合成成为可能。
Negishi Coupling for Highly Selective Syntheses of Allenes via Ligand Effect and Mechanistic Study via SAESI‐MS/MS
Assisted Electrospray Ionization Mass Spectrometry) has been applied to successfully capture the highly reactive organometallic intermediates, which show the different coordination behaviors of Pd with SPhos or Gorlos‐Phos as the ligand in the catalytic cycle. In addition, the different reactivities of Int 1 and Int 2 towards the formation of the final allene products have been demonstrated via SAESI‐MS/MS
在过渡金属催化的反应中,β-H的消除是一个固有的问题。我们在此描述了一个有趣的Et 2 Zn分别充当乙基提供者或H提供者的配体效应:通过应用SPhos或Gorlos-Phos作为配体,已成功在相应的Negishi偶联反应中控制了β-H的消除,从而提供了不同的聚预取代的异戊烯,收率高,选择性好。SAESI-MS(š olvent甲ssisted é lectrospray我onization中号屁股小号光谱法)已成功地捕获了高反应性的有机金属中间体,这些中间体在催化循环中显示出Pd与SPhos或Gorlos-Phos作为配体的不同配位行为。此外,通过SAESI-MS / MS实验证明了Int 1和Int 2对最终丙二烯产物形成的不同反应性。这些质谱研究可视化了Negishi偶联反应的整个催化循环,同时很好地解释了所观察到的反应性和选择性。
Site-selective C–H activation and regiospecific annulation using propargylic carbonates
The weakly coordinating carboxylic acid moiety outperformed other typically used directing groups in C–Hactivation, including ketone, nitrile, sulfonamide, amide and strongly coordinating nitrogen heterocycles. This is an important step towards the application of C–Hactivationreactions in complex (functional) real-world molecules.
A palladium-catalyzed multicomponent reaction (MCR) of propargylic carbonates with isocyanides is reported. Remarkably, the orderly insertion of isocyanides affords two types of valuable N-heterocyclic products (Z)-6-imino-4,6-dihydro-1H-furo[3,4-b]pyrrol-2-amines and (E)-5-iminopyrrolones in high yields. Systematic analysis of the reaction conditions indicates that the selectivity of these N-heterocyclic
报道了炔丙基碳酸酯与异氰酸酯的钯催化的多组分反应(MCR)。值得注意的是,有序插入异氰酸酯可提供两种有价值的N-杂环产物(Z)-6-亚氨基-4,6-二氢-1 H-呋喃[3,4- b ]吡咯-2-胺和(E) -5-亚氨基吡咯烷酮产量高。反应条件的系统分析表明,这些N-杂环产物的选择性可以通过配体和温度控制。
Umpolung coupling of pyridine-2-carboxaldehydes and propargylic carbonates <i>via</i> N-heterocyclic carbene/palladium synergetic catalysis
作者:Weiyang Bi、Yunhui Yang、Song Ye、Congyang Wang
DOI:10.1039/d1cc01311d
日期:——
reaction of pyridine-2-carboxaldehydes and propargylic carbonates has been developed for the first time through N-heterocycliccarbene/palladium cooperative catalysis with the judicious selection of the palladium catalyst, ligand and N-heterocycliccarbene, giving the propargylic ketones regioselectively.