Rhodium(III)-Catalyzed CH Activation of Arenes Using a Versatile and Removable Triazene Directing Group

Copper-catalyzed peri-selective direct sulfenylation of 1-naphthylamines with disulfides

A copper-catalyzed peri-selective direct C–H sulfenylation of 1-naphthylamines with disulfides was developed.

Rh(III)-catalyzed oxidative ortho-C–H alkylation of 2,4-diarylquinazoline with potassium alkyltrifluoroborates

Alkyltrifluoroborates were used for Rh(III)-catalyzed ortho-alkylation of 2,4-disubstituted quinazoline via C–H bond activation. The reaction proceeded well with a broad substrate scope, providing a direct way to access high functional quinazoline core structure derivatives in yields up to 95%.

Copper-Catalyzed Direct Acyloxylation of C(sp2)-H Bonds in Aromatic Amides

Copper-catalyzed ortho-acyloxylation of the sp² C-H bond of aryl amides with carboxylic acids is reported. Benzoic acids, cinnamic acids, and aliphatic acids can be involved, and the desired products were obtained in moderate to good yields. This procedure is compatible with a wide range of functional groups and heteroarenes without the use of any ligands or additives. This method provides an operationally simple approach for the synthesis of benzoate and cinnamate.

Additive-Free Pd-Catalyzed α-Allylation of Imine-Containing Heterocycles

An additive-free Pd-catalyzed α-allylation of different imino-group-ontaining heterocycles is reported. The activation of α-CH pronucleophiles (pKa (DMSO) > 25) occurs without the addition of strong bases or Lewis acids using only the Pd/Xantphos catalyst system. The reaction scope has been studied for various 5- and 6-membered nitrogen-containing heterocycles (yields up to 96%). Mechanistic investigations suggest an initial allylation of the imine-N followed by a Pd-catalyzed formal aza-Claisen rearrangement.

Recent advances in positional-selective alkenylations: removable guidance for twofold C–H activation

Recent advances in transition-metal catalyzed positional-selective alkenylations via twofold C–H activation directed by removable or traceless directing groups are reviewed.

Palladium-catalyzed coupling of azoles with 1-aryltriazenes via C–H/C–N cleavage

Arylation of azoles was performed via C–H functionalization with 1-aryltriazenes in the presence of PdCl₂, dppe, CuCl and Bu^tOLi.

Unified synthesis of mono/bis-arylated phenols via RhIII-catalyzed dehydrogenative coupling

2,6-Bis-arylated phenols are rarely reported and are synthetically challenging. Directed C-H functionalization reactions, using a directing group (DG), might provide a convenient solution to their synthesis. However, this strategy usually results in partial cleavage of the directing group, preventing further/second C-H activation cascades. Herein we report a general strategy that allows for the precise control of the oxidation pathways so that directing groups can be either preserved or cleaved. We found that N-phenoxyacetamides could undergo ortho-arylation reactions with or without an external oxidant, yielding products with different oxidation states, notably the rare bis-arylated phenols. Notably, a unique rhodacycle intermediate was isolated, characterized by X-ray crystallography, and confirmed to be an active catalyst. Switching between internal and external oxidation could be a general strategy in diverse directed C-H functionalization reactions to realize bis-functionalized products.

Oxidation of diazenyl-protected N-heterocycles – a new entry to functionalized lactams

A strategy for the synthesis ofN-aryldiazenyllactams, offering the direct access to protected lactam derivatives, is based on the oxidation of the corresponding cyclic amines with a ruthenium-based catalyst in CCl₄/CAN/phosphate buffer.

Palladium(ii)-catalyzed ortho-C–H olefination of phenylalanine and phenylethylamine derivatives directed by removable picolinamide group

Palladium-catalyzed ortho-C–H olefination of phenylalanine and phenylethylamine derivatives assisted by a removable picolinamide group has been achieved.

Catalytic Reductive ortho-C-H Silylation of Phenols with Traceless, Versatile Acetal Directing Groups and Synthetic Applications of Dioxasilines

A new, highly selective, bond functionalization strategy, achieved via relay of two transition metal catalysts and the use of traceless acetal directing groups, has been employed to provide facile formation of C-Si bonds and concomitant functionalization of a silicon group in a single vessel. Specifically, this approach involves the relay of Ir-catalyzed hydrosilylation of inexpensive and readily available phenyl acetates, exploiting disubstituted silyl synthons to afford silyl acetals and Rh-catalyzed ortho-C-H silylation to provide dioxasilines. A subsequent nucleophilic addition to silicon removes the acetal directing groups and directly provides unmasked phenol products and, thus, useful functional groups at silicon achieved in a single vessel. This traceless acetal directing group strategy for catalytic ortho-C-H silylation of phenols was also successfully applied to preparation of multisubstituted arenes. Remarkably, a new formal α-chloroacetyl directing group has been developed that allows catalytic reductive C-H silylation of sterically hindered phenols. In particular, this new method permits access to highly versatile and nicely differentiated 1,2,3-trisubstituted arenes that are difficult to access by other catalytic routes. In addition, the resulting dioxasilines can serve as chromatographically stable halosilane equivalents, which allow not only removal of acetal directing groups but also introduce useful functional groups leading to silicon-bridged biaryls. We demonstrated that this catalytic C-H bond silylation strategy has powerful synthetic potential by creating direct applications of dioxasilines to other important transformations, examples of which include aryne chemistry, Au-catalyzed direct arylation, sequential orthogonal cross-couplings, and late-stage silylation of phenolic bioactive molecules and BINOL scaffolds.

Cationic Cobalt(III) Catalyzed Indole Synthesis: The Regioselective Intermolecular Cyclization of N-Nitrosoanilines and Alkynes

The unique regioselectivity and reactivity of cobalt(III) in the direct cyclization of N-nitrosoanilines with alkynes for the expedient synthesis of N-substituted indoles is demonstrated. In the presence of a cobalt(III) catalyst, high regioselectivity was observed when using unsymmetrical meta-substituted N-nitrosoanilines. Moreover, internal alkynes bearing electron-deficient groups, which are almost unreactive in the [Cp*Rh(III)]-catalyzed system, display good reactivity in this transformation.

Palladium-catalyzed carbonylative Sonogashira coupling between aryl triazenes and alkynes

We developed a palladium-catalyzed carbonylative Sonogashira reaction with aryl triazenes and alkynes as substrates and methanesulfonic acid as the additive. A series of α,β-ynones were synthesized by this alternative procedure. Notably, bromides, iodides and hydroxyl groups could be well-tolerated under these reaction conditions.

Iron-mediated oxidative C–H coupling of arenes and alkenes directed by sulfur: an expedient route to dihydrobenzofurans

A route to medicinally-relevant dihydrobenzofurans utilises a sulfur-directed, iron-mediated C–H ortho-coupling of arenes and alkenes, and a palladium-catalysed heterocyclisation.

Pd-Catalyzed sequential β-C(sp3)–H arylation and intramolecular amination of δ-C(sp2)–H bonds for synthesis of quinolinones via an N,O-bidentate directing group

An effective protocol for the synthesis of quinolinone derivatives by palladium-catalyzed sequential β-C(sp³)–H arylation and selective intramolecular C(sp²)–H/N–H amination is developed.

Advances in the development of catalytic tethering directing groups for C–H functionalization reactions

Inspired by the development of organocatalysis, transition-metal-catalyzed C–H functionalization reactions using tethering groups to accomplish site-selectivity catalytically have been demonstrated.

Relayed Regioselective Alkynylation/Olefination of Unsymmetrical Cyclic Diaryliodonium Species Catalyzed by Cu and Pd: Affording Fluorescent Cytotoxic Benzoxazoles

Although cyclic diaryliodonium species have the potential to act as valuable synthons for cascade transformations, they still remain largely unexplored. The regioselectivity associated with unsymmetrical cyclic diaryliodonium species has previously been known to pose a challenge. A regioselective relayed alkynylation and olefination of unsymmetrical cyclic diaryliodonium species has been achieved by installation of a directing amido group. These relayed transformations were delayed until an oxazole ring had formed, delivering a series of unique fluorescent benzoxazoles. Moreover, some of these synthetic benzoxazoles showed apparent inhibitory activity against malignant cancer cells. Further confocal visualization revealed that benzoxazoles targeted cell nuclei. These findings might provide a novel structural scaffold to develop desirable anticancer agents.