1232692-92-0Relevant articles and documents
The pyridyldiisopropylsilyl group: A masked functionality and directing group for monoselective ortho-Acyloxylation and ortho-Halogenation reactions of arenes
Huang, Chunhui,Chernyak, Natalia,Dudnik, Alexander S.,Gevorgyan, Vladimir
supporting information; experimental part, p. 1285 - 1305 (2011/07/07)
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 room-temperature 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 alkynyldesilylations, 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 (kH/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.
A general strategy toward aromatic 1,2-ambiphilic synthons: Palladium-catalyzed ortho-halogenation of PyDipSi-arenes
Dudnik, Alexander S.,Chernyak, Natalia,Huang, Chunhui,Gevorgyan, Vladimir
supporting information; experimental part, p. 8729 - 8732 (2011/01/06)
A general and efficient strategy to synthesize 1,2-ambiphilic aromatic and heteroaromatic synthons from haloarenes has been developed. The method involves installation of the PyDipSi directing group, and subsequent palladium-catalyzed directed ortho-halogenation of aryl silanes (see scheme; Py=2-pyridyl). The usefulness of these 1,2-ambiphilic building blocks was shown in their participation as both nucleophilic aryl silane and electrophilic aryl iodide moieties.
