Ru-catalysed C-H arylation of indoles and pyrroles with boronic acids: scope and mechanistic studies

The Ru-catalysed C2–H arylation of indoles and pyrroles by using boronic acids under oxidative conditions is reported. This reaction can be applied to tryptophan derivatives and tolerates a wide range of functional groups on both coupling partners, including bromides and iodides, which can be further derivatised selectively. New indole-based ruthenacyclic complexes are described and investigated as possible intermediates in the reaction. Mechanistic studies suggest the on-cycle intermediates do not possess a para-cymene ligand and that the on-cycle metalation occurs through an electrophilic attack by the Ru centre.

Application of bis(oxazoline) in asymmetric β-amination of chalcones

A variety of β-imidoketone derivatives containing various functional groups were obtained with high enantioselectivities.

Practical and highly selective C-H functionalization of structurally diverse ethers

A trityl ion mediated C-H functionalization of ethers with a wide range of nucleophiles at ambient temperature has been developed. The reaction displays high chemoselectivity and good functional group tolerance. The protocol also exhibits excellent regio- and diastereoselectivities for the unsymmetric ethers, thus stereoselectively generating highly functionalized disubstituted 2,5-trans tetrahydrofurans (THF), 2,6-trans tetrahydropyrans (THP), 2,6-trans dihydropyrans (DHP), and 1,3-trans isochromans, and highlighting the capacity of the protocol in complex molecule synthesis.

Oxidant-free dehydrogenative coupling reactions via hydrogen evolution

Oxidant-free dehydrogenative coupling reactions: Recently, coupling reactions have followed a novel strategy for the construction of C==C, C==N, C==P, and S==S bonds by dehydrogenation without using any extra oxidant, via H2 evolution. These breakthroughs inspire a new direction in the construction of chemical bonds, towards more sustainable, highly atom-economical, and environmentally benign synthetic methods.

Copper-catalyzed oxidative dimerizations of 3-N-hydroxy-aminoprop-1-enes to form 1,4-dihydroxy-2,3-diaminocyclohexanes with C2 symmetry

This work describes the one-step construction of complex and important molecular frameworks through copper-catalyzed oxidations of cheap tertiary amines. Copper-catalyzed aerobic oxidations of N-hydroxyaminopropenes to form C2 -symmetric N- and O-functionalized cyclohexanes are described. Such catalytic oxidations proceed with remarkable stereocontrol and high efficiency. Reductive cleavage of the two NO bonds of these products delivers 1,4-dihydroxy-2,3-diaminocyclohexanes, which are important skeletons of several bioactive molecules.

Aldehyde-assisted ruthenium(II)-catalyzed C-H oxygenations

Versatile ruthenium(II) complexes allow for site-selective C-H oxygenations with weakly-coordinating aldehydes. The challenging C-H functionalizations proceed with high chemoselectivity by rate-determining C-H metalation. The new method features an ample substrate scope, which sets the stage for the step-economical preparation of various bioactive heterocycles.

Aniline carbamates: a versatile and removable motif for palladium-catalyzed directed C-H activation

The aniline carbamate is introduced as a new removable directing group for C-H activation. Its versatility and ability as a directing group are demonstrated by its use in the ortho-arylation of a wide variety of aniline derivatives under palladium(II) catalysis, with symmetric diaryliodonium salts as aryl donors. The reaction differs from previously reported arylations in its selectivity and its mechanism, as elucidated by kinetic and isotopic experiments. The directing group can also be easily removed under a variety of conditions.

Triazole-assisted ruthenium-catalyzed C-H arylation of aromatic amides

Site-selective ruthenium(II)-catalyzed direct arylation of amides was achieved through CH cleavages with modular auxiliaries, derived from easily accessible 1,2,3-triazoles. The triazolyldimethylmethyl (TAM) bidentate directing group was prepared in a highly modular fashion through copper(I)-catalyzed 1,3-dipolar cycloaddition and allowed for ruthenium-catalyzed CH arylations on arenes and heteroarenes, as well as alkenes, by using easy-to-handle aryl bromides as the arylating reagents. The triazole-assisted CH activation strategy was found to be widely applicable, to occur under mild reaction conditions, and the catalytic system was tolerant of important electrophilic functionalities. Notably, the flexible triazole-based auxiliary proved to be a more potent directing group for the optimized ruthenium(II)-catalyzed direct arylations, compared with pyridyl-substituted amides or substrates derived from 8-aminoquinoline.