Transition metal-catalyzed arylation of unactivated C(sp3)-H bonds

The C-H activation/1,3-diyne strategy: highly selective direct synthesis of diverse bisheterocycles by Rh(III) catalysis

The reactivity and selectivity of 1,3-diynes in transition-metal-catalyzed CH activation is exploited to quickly assemble diverse polysubstituted bisheterocycles, which are highly important but difficult to access. By using the CH activation/1,3-diyne strategy, we overcame the challenges of selectivity (chemo-, regio-, and mono-/diannulation) and constructed seven kinds of adjacent bisheterocycles through the formation of four strategic bonds with high efficiency and high selectivity.

Synthesis and C2-functionalization of indoles with allylic acetates under rhodium catalysis

Tandem rhodium-catalyzed oxidative allylation and annulation of acetanilides with allyl acetate to afford the corresponding indoles are described. In addition, the site-selective C2 allylation, crotylation and prenylation of indoles using allylic acetates under rhodium catalysis are reported.

Rh(III)-catalyzed oxidative coupling of 1,2-disubstituted arylhydrazines and olefins: a new strategy for 2,3-dihydro-1H-indazoles

A rhodium(III)-catalyzed oxidative olefination of 1,2-disubstituted arylhydrazines with alkenes via sp(2) C-H bond activation followed by an intramolecular aza-Michael reaction is described. This strategy allows the direct and efficient construction of highly substituted 2,3-dihydro-1H-indazole scaffolds.

Chemo- and regioselective C(sp³)-H arylation of unactivated allylarenes by deprotonative cross-coupling

The combination of aryl bromides, allylbenzene, base and a palladium catalyst usually results in a Heck reaction. Herein we combine these same reagents, but override the Heck pathway by employing a strong base. In the presence of LiN(SiMe3)2, allylbenzene derivatives undergo reversible deprotonation. Transmetalation of the resulting allyllithium intermediate to LPdAr(Br) and reductive elimination provide the 1,1-diarylprop-2-enes, which are not accessible by the Heck reaction. The regioselectivity in this deprotonative cross-coupling process is catalyst-controlled and very high.

Regioselective and guided C-H activation of 4-nitropyrazoles

A divergent and regioselective approach to 5-aryl-4-nitro-1H-pyrazoles was developed by guided transition-metal-catalyzed arylation of 4-nitro-1H-pyrazoles. This method provides a convenient tool for the functionalization of the pharmacologically relevant pyrazole scaffold. The scope and limitations of the methodology were studied.

Ligand-controlled C(sp³)-H arylation and olefination in synthesis of unnatural chiral α-amino acids

The use of ligands to tune the reactivity and selectivity of transition metal catalysts for C(sp(3))-H bond functionalization is a central challenge in synthetic organic chemistry. Herein, we report a rare example of catalyst-controlled C(sp(3))-H arylation using pyridine and quinoline derivatives: The former promotes exclusive monoarylation, whereas the latter activates the catalyst further to achieve diarylation. Successive application of these ligands enables the sequential diarylation of a methyl group in an alanine derivative with two different aryl iodides, affording a wide range of β-Ar-β-Ar'-α-amino acids with excellent levels of diastereoselectivity (diastereomeric ratio > 20:1). Both configurations of the β-chiral center can be accessed by choosing the order in which the aryl groups are installed. The use of a quinoline derivative as a ligand also enables C(sp(3))-H olefination of a protected alanine.

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.

Iridium-catalyzed intermolecular amidation of sp³ C-H bonds: late-stage functionalization of an unactivated methyl group

Reported herein is the iridium-catalyzed direct amidation of unactivated sp(3) C-H bonds. With sulfonyl and acyl azides as the amino source, the amidation occurs efficiently under mild conditions over a wide range of unactivated methyl groups with high functional group tolerance. This procedure can be successfully applied for the direct introduction of an amino group into complex compounds and thus can serve as a powerful synthetic tool for late-stage C-H functionalization.

Direct access to isoindolines through tandem Rh(III)-catalyzed alkenylation and cyclization of N-benzyltriflamides

The rhodium-catalyzed oxidative alkenylation of N-benzyltriflamides with olefins followed by an intramolecular cyclization via C-H bond activation is described. This method results in the direct and efficient synthesis of highly substituted isoindoline frameworks.

A General and Practical Palladium-Catalyzed Direct α-Arylation of Amides with Aryl Halides

An efficient system for the direct catalytic intermolecular α-arylation of acetamide derivatives with aryl bromides and chlorides is presented. The palladium catalyst is supported by Kwong's indole-based phosphine ligand and provides monoarylated amides in up to 95% yield. Excellent chemoselectivities (>10:1) in the mono- and diarylation with aryl bromides were achieved by careful selection of bases, solvents, and stoichiometry. Under the coupling conditions, the weakly acidic α-protons of amides (pKa up to 35) were reversibly depotonated by LiO t Bu, NaO t Bu, or NaN(SiMe3)2.

Nickel-catalyzed direct arylation of C(sp3)-H bonds in aliphatic amides via bidentate-chelation assistance

The Ni-catalyzed, direct arylation of C(sp(3))-H (methyl and methylene) bonds in aliphatic amides containing an 8-aminoquinoline moiety as a bidentate directing group with aryl halides is described. Deuterium-labeling experiments indicate that the C-H bond cleavage step is fast and reversible. Various nickel complexes including both Ni(II) and Ni(0) show a high catalytic activity. The results of a series of mechanistic experiments indicate that the catalytic reaction does not proceed through a Ni(0)/Ni(II) catalytic cycle, but probably through a Ni(II)/Ni(IV) catalytic cycle.

Ligand-enabled cross-coupling of C(sp3)-H bonds with arylboron reagents via Pd(II)/Pd(0) catalysis

There have been numerous developments in C–H activation reactions in the past decade. Attracted by the ability to directly functionalize molecules at ostensibly unreactive C–H bonds, chemists have discovered reaction conditions that enable reaction of C(sp²)–H and C(sp³)–H bonds with a variety of coupling partners. Despite these advances, the development of suitable ligands that enable catalytic C(sp³)–H bond functionalization remains a significant challenge. Here, we report the discovery of a mono-N-protected amino acid (MPAA) ligand that enables Pd(II)-catalyzed coupling of γ-C(sp³)–H bonds in triflyl-protected amines (R–NHTf) with arylboron reagents. Remarkably, no background reaction was observed in the absence of ligand. A variety of amine substrates and arylboron reagents were cross-coupled using this method. Arylation of optically active amino acid-derived substrates also provides a potential route for preparing non-protenogenic amino acids.

Versatile reactivity of Pd-catalysts: mechanistic features of the mono-N-protected amino acid ligand and cesium-halide base in Pd-catalyzed C–H bond functionalization

The C–H functionalization strategies, complexity in Pd-catalyzed chemical transformations, unprecedented Pd-clustering, base (Cs-halide) and weakly coordinated amino acid ligand effects.

Pd(ii)-Catalyzed arylation of unactivated methylene C(sp3)–H bonds with aryl halides using a removable auxiliary

Pd(ii)-catalyzed arylation of methylene C(sp³)–H bonds with ArBr directed by our newly developed PIP auxiliary was reported.

A general Pd/Cu-catalyzed C–H heteroarylation of 3-bromoquinolin-2(1H)-ones

The Pd(OAc)₂/CuI system effectively catalyzes the coupling of 3-bromoquinolin-2(1H)-ones with a series of azoles to give 3-(heteroaryl)quinolin-2(1H)-ones in good yields.