The cross-dehydrogenative coupling of C(sp3)-H bonds: a versatile strategy for C-C bond formations

Controlled regiodivergent C-H bond activation of imidazo[1,5-a]pyridine via synergistic cooperation between aluminum and nickel

The catalytic method features a cooperative interaction between Ni and Al imparting remote C-H alkenylation at the C5 position of imidazo[1,5-a]pyridine with alkynes at mild conditions. Exclusion of AlMe3 switches the selectivity to the C3 position. Reactions with styrene and other olefinic substrates affording C5-adducts by Ni/Al catalysis are also included.

Late-stage diversification of peptides by metal-free C-H arylation

The bioorthogonal late-stage diversification of functionalized oligopeptides was accomplished through a metal-free, site-selective C-H arylation of engineered indole derivatives under mild reaction conditions.

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.

Tip-induced C-H activation and oligomerization of thienoanthracenes

The tip of a scanning tunneling microscope (STM) can be used to dehydrogenate freely-diffusing tetrathienoanthracene (TTA) molecules on Cu(111), trapping the molecules into metal-coordinated oligomeric structures. The process proceeds at bias voltages above ~3 V and produces organometallic structures identical to those resulting from the thermally-activated cross-coupling of a halogenated analogue. The process appears to be substrate dependent: no oligomerization was observed on Ag(111) or HOPG. This approach demonstrates the possibility of controlled synthesis and nanoscale patterning of 2D oligomer structures on selected surfaces.

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.

Redox-neutral α-sulfenylation of secondary amines: ring-fused N,S-acetals

Secondary amines react with thiosalicylaldehydes in the presence of catalytic amounts of acetic acid to generate ring-fused N,S-acetals in redox-neutral fashion. A broad range of amines undergo α-sulfenylation, including challenging substrates such morpholine, thiomorpholine, and piperazines. Computational studies employing density functional theory indicate that acetic acid reduces the energy barriers of two separate steps, both of which involve proton transfer.

The redox-Mannich reaction

A complement to the classic three-component Mannich reaction, the redox-Mannich reaction, utilizes the same starting materials but incorporates an isomerization step that enables the facile preparation of ring-substituted β-amino ketones. Reactions occur under relatively mild conditions and are facilitated by benzoic acid.

The Redox-A3 Reaction

This Highlight details the recent emergence of a new type of A3 reaction (three-component condensation of an amine, an aldehyde and an alkyne). In contrast to the classic A3 coupling process, the redox-A3 reaction incorporates an iminium isomerization step and leads to amine α-alkynylation. The overall transformation is redox-neutral by virtue of a combined reductive N-alkylation/oxidative C-H bond functionalization.

Dual C-H functionalization of N-aryl amines: synthesis of polycyclic amines via an oxidative Povarov approach

Iminium ions generated in situ via copper(I) bromide catalyzed oxidation of N-aryl amines readily undergo [4 + 2] cycloadditions with a range of dienophiles. This method involves the functionalization of both a C(sp(3))-H and a C(sp(2))-H bond and enables the rapid construction of polycyclic amines under relatively mild conditions.

TBHP-Mediated C–H Thiolation of Tetrahydrofuran with Disulfides Promoted by Catalytic Amounts of Na2CO3

An efficient route to constructing C–S bonds has been developed by TBHP ( tert-butyl hydroperoxide) mediated C–H thiolation of tetrahydrofuran with disulfides. This route is promoted by catalytic amounts of Na2CO3 and gives various tetrahydrofuran-containing sulfides in moderate to high yields.

Ruthenium(II)-catalyzed C(sp3)-H α-alkylation of pyrrolidines

A catalytic system comprising [RuCl2(PPh3)3], AgOTf, and BINAP enabled atom- and step-economical additions of C(sp(3))-H bonds onto unactivated alkenes 2 under comparably mild reaction conditions. The pyridyl directing group was easily removed to furnish the corresponding (NH)-free amines with ample scope.