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A trimetallic palladium/copper/silver system has been developed that allows the decarboxylative Hiyama coupling of ortho-substituted aryl carboxylates with trialkoxyarylsilanes to give the corresponding biaryls. The cross-coupling is catalyzed by a Pd/N-heterocyclic carbene complex with silver carbonate aiding its reoxidation. Copper(II) fluoride acts as decarboxylation catalyst, stoichiometric oxidant, and fluoride source. The scope of the protocol is demonstrated by 22 examples, among them aryl halides suitable for further coupling, and the synthetic utility of the products is illustrated by their conversion into carbazoles and 1 H-indazoles. [ABSTRACT FROM AUTHOR]

Two bulky, chiral, monodentate N-heterocyclic carbene ligands were applied to palladium-catalyzed asymmetric CH arylation to incorporate C(sp3)H bond activation. Racemic mixtures of the carbamate starting materials underwent regiodivergent reactions to afford different trans-2,3-substituted indolines. Although this CArCalkyl coupling requires high temperatures (140-160 °C), chiral induction is high. This regiodivergent reaction, when carried out with enantiopure starting materials, can lead to single structurally different enantiopure products, depending on the catalyst chirality. The CH activation at a tertiary center was realized only in the case of a cyclopropyl group. No CH activation takes place alpha to a tertiary center. A detailed DFT study is included and analyses of methyl versus methylene versus methine CH activation is used to rationalize experimentally observed regio- and enantioselectivities. [ABSTRACT FROM AUTHOR]

Palladium complexes incorporating chiral N-heterocyclic carbene (NHC) ligands catalyze the asymmetric intramolecular α-arylation of amides producing 3,3-disubstituted oxindoles. Comprehensive DFT studies have been performed to gain insight into the mechanism of this transformation. Oxidative addition is shown to be rate-determining and reductive elimination to be enantioselectivity-determining. The synthesis of seven new NHC ligands is detailed and their performance is compared. One of them, L8, containing a tBu and a 1-naphthyl group at the stereogenic centre, proved superior and was very efficient in the asymmetric synthesis of fifteen new spiro-oxindoles and three azaspiro-oxindoles often in high yields (up to 99 %) and enantioselectivities (up to 97 % ee; ee=enantiomeric excess). Three palladacycle intermediates resulting from the oxidative addition of [Pd(NHC)] into the aryl halide bond were isolated and structurally characterized (X-ray). Using these intermediates as catalysts showed alkene additives to play an important role in increasing turnover number and frequency. [ABSTRACT FROM AUTHOR]