The Pyridyldiisopropylsilyl Group: A Masked Functionality and Directing Group for Monoselective ortho-Acyloxylation and ortho-Halogenation Reactions of Arenes.
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TLDR
A general mechanism involving the formation of a palladacycle via a C-H activation process as the rate-determining step has been proposed, and the silicon-tethered directing group in both acyloxylated and halogenated products can easily be removed or efficiently converted into an array of other valuable functionalities.Abstract:
A novel, easily removable and modifiable silicon-tethered pyridyldiisopropylsilyl directing group for C—H functionalizations of arenes has been developed. The installation of the pyridyldiisopropylsilyl group can efficiently be achieved via two complementary routes using easily available 2-(diisopropylsilyl)pyridine (5). The first strategy features a nucleophilic hydride substitution at the silicon atom in 5 with aryllithium reagents generated in situ from the corresponding aryl bromides or iodides. The second milder route exploits a highly efficient roomtemperature rhodium(I)-catalyzed cross-coupling reaction between 5 and aryl iodides. The latter approach can be applied to the preparation of a wide range of pyridyldiisopropylsilyl-substituted arenes possessing a variety of functional groups, including those incompatible with organometallic reagents. The pyridyldiisopropylsilyl directing group allows for a highly efficient, regioselective palladium(II)-catalyzed mono-ortho-acyloxylation and ortho-halogenation of various aromatic compounds. Most importantly, the silicon-tethered directing group in both acyloxylated and halogenated products can easily be removed or efficiently converted into an array of other valuable functionalities. These transformations include protio-, deuterio-, halo-, boro-, and alkynyl-desilylations, as well as a conversion of the directing group into the hydroxy functionality. In addition, the construction of aryl-aryl bonds via the Hiyama―Denmark cross-coupling reaction is feasible for the acetoxylated products. Moreover, the ortho-halogenated pyridyldiisopropylsilylarenes, bearing both nucleophilic pyridyldiisopropylsilyl and electrophilic aryl halide moieties, represent synthetically attractive 1,2-ambiphiles. A unique reactivity of these ambiphiles has been demonstrated in efficient syntheses of arylenediyne and benzosilole derivatives, as well as in a facile generation of benzyne. In addition, preliminary mechanistic studies of the acyloxylation and halogenation reactions have been performed. A trinuclear palladacycle intermediate has been isolated from a stoichiometric reaction between diisopropyl-(phenyl)pyrid-2-ylsilane (3a) and palladium acetate. Furthermore, both C―H functionalization reactions exhibited equally high values of the intramolecular primary kinetic isotope effect (k H /k D =6.7). Based on these observations, a general mechanism involving the formation of a palladacycle via a C―H activation process as the rate-determining step has been proposed.read more
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A comprehensive overview of directing groups applied in metal-catalysed C-H functionalisation chemistry.
Carlo Sambiagio,David Schönbauer,Remi Blieck,Toan Dao-Huy,Gerit Pototschnig,Patricia Schaaf,Thomas Wiesinger,Muhammad Farooq Zia,Joanna Wencel-Delord,Tatiana Besset,Bert U. W. Maes,Michael Schnürch +11 more
TL;DR: The present review is devoted to summarizing the recent advances (2015–2017) in the field of metal-catalysed group-directed C–H functionalisation.
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Recent Advances in Transition-Metal-Catalyzed Synthetic Transformations of Organosilicon Reagents
TL;DR: In this article, a cross-coupling of organosilicon reagents with organic halides or pseudohalides has been considered to be a useful tool for constructing the carbon frameworks of various target molecules such as pharmaceuticals and π-conjugated functional materials.
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Silanol: a traceless directing group for Pd-catalyzed o-alkenylation of phenols.
TL;DR: A silanol-directed, Pd(II)-catalyzed C-H alkenylation of phenols is reported, which allows for efficient synthesis of diverseAlkenylated phenols, including an estrone derivative.
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Meta-selective C-H functionalization using a nitrile-based directing group and cleavable Si-tether.
TL;DR: A nitrile-based template that enables meta-selective C-H bond functionalization was developed and uses a silicon atom for attachment, allowing for a facile introduction/deprotection strategy increasing the synthetic practicality of this template.
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Cross-dehydrogenative coupling for the intermolecular C–O bond formation
TL;DR: The present review summarizes primary publications on the cross-dehydrogenative C–O coupling, with special emphasis on the studies published after 2000, and classes the data according to the structures of C-reagents and the type of oxidative systems.
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