Palladium‐Catalyzed Direct C−H Olefination of Polyfluoroarenes with Alkenyl Tosylates

Yee, Ka Yee; Leung, Man-Tak; Tse, Man Ho; Choy, Pui Ying; Kwong, Fuk Yee

doi:10.1002/ejic.202200288

Cited by 2 publications

(2 citation statements)

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“…50 Very recently, the first direct C−H olefination of polyfluoroarenes with alkenyl tosylates was reported using the [(BPA)PdOMs] 2 /L6 catalyst system with PivOH as an additive (Scheme 15C). 51 Initial ligand screening revealed that WK-phos with two orthomethoxy groups surprisingly suppressed the reaction when compared with structurally similar PCy 2 -Andole-phos (16 vs 24% yield, respectively). It is believed that the larger proximal steric hindrance of WK-phos was responsible for the decreased product yield.…”

Section: Direct C−h Functionalizationmentioning

confidence: 99%

“…Later, the arylation of polyfluoroarenes with sterically congested aryl chlorides was achieved using a C3-type indolylphosphine ligand containing the −PPh 2 moiety (Scheme B) . Very recently, the first direct C–H olefination of polyfluoroarenes with alkenyl tosylates was reported using the [(BPA)PdOMs] 2 / L6 catalyst system with PivOH as an additive (Scheme C) . Initial ligand screening revealed that WK-phos with two ortho -methoxy groups surprisingly suppressed the reaction when compared with structurally similar PCy 2 -Andole-phos (16 vs 24% yield, respectively).…”

Section: C3-type Monophosphorus Ligandsmentioning

confidence: 99%

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Facile Assembly of Modular-Type Phosphines for Tackling Modern Arylation Processes

2022

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Conspectus This Account presents an overview of a promising collection of phosphine ligands simply made from the modular Fischer indolization process and their applications in modern arylation processes. Using one easily accessible 2-arylindole scaffold, three major phosphino-moiety-positioned ligand series can be readily generated. We have attempted to explore challenging electrophilic and nucleophilic partners for the coupling reaction using the modular ligand tool. For the electrophilic partner study, CM-phos-type ligands, where the phosphino group is located at the 2-arene position of 2-arylindole, allow the successful cross-coupling of aryl mesylates. The CM-phos ligand forms a palladacycle before entering the cross-coupling catalytic cycle. For the nucleophilic partner investigation, the indole C3-positioned phosphines show the first accomplishment of Pd-catalyzed organotitanium nucleophile arylation. Indeed, the aryl-titanium nucleophile undergoes cross-coupling more efficiently than does the organoboron coupling partner in particular cases. Moreover, in the indole C3-positioned phosphine series, the −PPh2-containing ligands perform better in the highly sterically hindered cross-coupling of aryl chlorides than do ligands containing the −PCy2 moiety. The catalyst loading can even be reduced to 0.2 mol % Pd for tetra-ortho-substituted biaryl synthesis. This finding offers a new perspective on the next-generation design of phosphine ligands in which the sterically bulky and electron-rich −PR2 group (R = alkyl) may not be necessary for the cross-coupling of aryl chlorides. In general, we hypothesize that a good balance of steric and electronic properties for entertaining the oxidative addition and reductive elimination steps is crucial to the success of the reaction. For the steric factor, the highly sterically congested −PR2 group normally favors the reductive elimination, yet we conjecture that this sterically bulky group would serve as an obstacle for the incoming aryl halides. For the electronic factor, the electron rich −PR2 group is believed to support the oxidative cleavage of the C(Ar)–Cl bond by donating more electron density to the corresponding σ* orbital. Nevertheless, the high electron richness of the −PR2 group may disfavor the reductive elimination electronically. Overall, an appropriate balance of both electron density and steric bulkiness is suggested to allow the sterically hindered cross-coupling to proceed smoothly. We have found that the −PPh2-containing ligand is a good starting point for this investigation. The formation of aromatic carbon–carbon (C–C) and carbon–heteroatom (C–X) bonds from aryl chlorides was successfully realized using our proprietary phosphines. In addition to the indole-core-bearing ligand skeleton, we also explored the relevant imidazolyl and carbazolyl phosphines for their unique applications. Interestingly, the carbazolyl ligand, having more flexible C–N axial chirality, displays particular interchangeable Pd–N and Pd–arene coordination, which facilitates both oxid...

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Section: Direct C−h Functionalizationmentioning

confidence: 99%

Section: C3-type Monophosphorus Ligandsmentioning

confidence: 99%