Palladium-Catalyzed para-C-H Arylation of Anilines with Aromatic Halides.

Controlling regioselectivity in C-H functionalizations is a key challenge in chemical method development. In arenes, functionalizations are most difficult to direct towards the C-H group furthest away from a substituent, in its para position. We herein demonstrate how the para-C-H arylation of anilines with non-activated aryl halides, elusive to date, is achieved by a base-assisted "metalla-tautomerism" approach. A proton is abstracted from the aniline substrate and replaced by an arylpalladium species, generated from the aryl halide coupling partner. In this step, the palladium is directed away from the N- to the tautomeric para-C-H position by a large phosphine ligand combined with a triphenylmethyl shielding group. The triphenylmethyl group is easily installed and removed, and can be recycled.

Halogen-Bridged Methylnaphthyl Palladium Dimers as Versatile Catalyst Precursors in Coupling Reactions.

Halogen-bridged methylnaphthyl (MeNAP) palladium dimers are presented as multipurpose Pd-precursors, ideally suited for catalytic method development and preparative organic synthesis. By simply mixing with phosphine or carbene ligands, they are in situ converted into well-defined monoligated complexes. Their catalytic performance was benchmarked against state-of-the-art systems in challenging Buchwald-Hartwig, Heck, Suzuki and Negishi couplings, and ketone arylations. Their use enabled record-setting activities, beyond those achievable by optimization of the ligand alone. The MeNAP catalysts permit syntheses of tetra-ortho-substituted arenes and bulky anilines in near-quantitative yields at room temperature, allow mono-arylations of small ketones, and enable so far elusive cross-couplings of secondary alkyl boronic acids with aryl chlorides.

Rhodium-Catalyzed Annelation of Benzoic Acids with α,ß-Unsaturated Ketones with Cleavage of C-H, CO-OH, and C-C Bonds.

In the presence of a [Cp*RhCl2 ]2 catalyst, the Lewis acid In(OTf)3 , and the mild base Na2 CO3 , aromatic carboxylates and α,ß-unsaturated ketones undergo a unique hydroarylation/Claisen/retro-Claisen process to give the corresponding indanones. In this carboxylate-directed ortho-C-H annelation, the C-COR bond of the ketone and the CO-OH group of the aromatic carboxylate are cleaved, and the hydroxy group is transferred from the aromatic to the aliphatic acyl residue. This reactivity is synthetically useful, particularly when starting from cyclic ketones, which are converted into indanones bearing aliphatic carboxylate side chains, thus greatly increasing the molecular complexity of aromatic carboxylates in a single step.

Dihalogen-bridged NHC-palladium(i) dimers: synthesis, characterisation and applications in cross-coupling reactions.

A di-iodo-bridged PdI dimer bearing an N-heterocyclic carbene ligand was made accessible via the reduction of [(IPr)PdI2]2 in basic methanol solution. The structural features of [(IPr)PdI]2 were explored by single-crystal X-ray analysis. It was found to be a convenient one-component precatalyst with high activity in Suzuki-Miyaura, Buchwald-Hartwig, and Sonogashira reactions.