Highly selective cross-coupling reactions of aryl(halo)silanes with aryl halides: A general and practical route to functionalized biaryls
摘要:
The palladium catalyzed cross-coupling reaction of aryl halides with aryl(halo)silanes (halogen= F, Cl) gives good yields of unsymmetrical biaryls and p-terphenyls. The reaction takes place smoothly in N,N-dimethylformamide in the presence of an appropriate palladium catalyst and potassium fluoride. Since this reaction is tolerant of a variety of reactive functional groups, highly functionalized 4,4'-, 3,4'-, 2,4'- and even sterically crowded 2,2'-disubstituted biaryls can be obtained in moderate to high yields. The synthetic utility of the method has been demonstrated by its application to a short synthesis of liquid crystals. Mechanistic aspects of transmetalation of an aryl(fluoro)silicate intermediate with a palladium complex are discussed on the basis of the substituent effects on the rate of the cross-coupling reactions.
Palladium Catalyzed Regioselective C4‐Arylation and Olefination of Indoles and Azaindoles
作者:Neetipalli Thrimurtulu、Arnab Dey、Anurag Singh、Kuntal Pal、Debabrata Maiti、Chandra M. R. Volla
DOI:10.1002/adsc.201801378
日期:2019.3.15
A convergent strategy for the synthesis of biologically relevant C4‐substituted indole scaffolds was demonstrated using Pd(II)‐catalyzed remote C−H functionalization of indoles and azaindoles. The reaction displays high regioselectivity for the C4‐position of indole‐3‐carbaldehydes using glycine as an inexpensive transient directing group. Notable features of this transformation include the selective
sequential tripleCHactivationreactiondirected by a pyrazole and an amide group leads to the well‐controlled construction of sterically congested dihydrobenzo[e]indazole derivatives. This cascade reaction demonstrates that the often problematic competing CHactivation pathways in the presence of multiple directinggroups can be harvested by design to improve step economy in synthesis. Pyrazole as a
由吡唑和酰胺基团引导的连续三重C - H活化反应导致空间拥挤的二氢苯并[e]吲唑衍生物的良好控制的结构。这种级联反应表明,在存在多个导向基团的情况下,经常存在问题的竞争性 C → H 活化途径可以通过设计来收获,以提高合成中的步骤经济性。吡唑作为相对较弱的配位基团首次被证明可以直接指导C - H活化。
Palladium-Catalyzed Reaction of Aryl Iodides with Acetic Anhydride. A Carbon Monoxide-Free Synthesis of Acetophenones
[reaction: see text] The palladium-catalyzed reaction of aryl iodides with aceticanhydride provides a straightforward and experimentally simple carbon monoxide-free route to acetophenones. The reaction tolerates a wide range of functionalized aryl iodides. Acetophenones are isolated in excellent yield with a variety of neutral, slightly electron-rich, and slightly electron-poor aryl iodides, whereas
PdII‐catalyzed C(sp3)−Harylation of saturatedheterocycles with a wide range of aryl iodides is enabled by an N‐heterocyclic carbene (NHC) ligand. A C(sp3)−H insertion step by the PdII/NHC complex in the absence of ArI is demonstrated experimentally for the first time. Experimental data suggests that the previously established NHC‐mediated Pd0/PdII catalytic manifold does not operate in this reaction