A Redox Transmetalation Step in Nickel-Catalyzed C-C Coupling Reactions.

Ni-catalyzed C-H functionalization reactions are becoming efficient routes to access a variety of functionalized arenes, yet the mechanisms of these catalytic C-C coupling reactions are not well understood. Here, we report the catalytic and stoichiometric arylation reactions of a nickel(II) metallacycle. Treatment of this species with silver(I)-aryl complexes results in facile arylation, consistent with a redox transmetalation step.

Copper-Catalyzed Decarboxylative Elimination of Carboxylic Acids to Styrenes.

A copper-catalyzed decarboxylative elimination reaction of (hetero)aromatic propionic acids to vinyl (hetero)arenes has been developed. This method furnishes alkenes from carboxylic acids without the need for stochiometric Pb or Ag additives or expensive or specialized photocatalysts. A series of mechanistic experiments indicate that the reaction proceeds via benzylic deprotonation and subsequent radical decarboxylation; a pathway that is distinct from the single-electron-transfer mechanisms implicated in related decarboxylative elimination reactions.

Aerobic Oxidation Reactivity of Well-Defined Cobalt(II) and Cobalt(III) Aminophenol Complexes.

This paper describes the synthesis and reactivity studies of three cobalt complexes bearing aminophenol-derived ligands without nitrogen substitution: Co(APH)(AP) (), Co(APH)(AP)(μ-BAP) (), and Co(AP) (), where APH = 2-amino-4,6-di--butylphenol, AP = 2-amino-4,6-di--butylphenolate, and μ-BAP = bridging 2-amido-4,6-di--butylphenolate. Stoichiometric reactivity studies of these well-defined complexes demonstrate the catalytic competency of both cobalt(II) and cobalt(III) complexes in the aerobic oxidative cyclization of APH with -butylisonitrile. Reactions with O reveal the aerobic oxidation of the cobalt(II) complex to generate the cobalt(III) species and .

Cobalt-Catalyzed Aerobic Oxidative Cyclization of 2-Aminophenols with Isonitriles: 2-Aminophenol Enabled O Activation by Cobalt(II).

An aerobic cobalt-catalyzed oxidative cyclization of 2-aminophenols and isonitriles is reported. These additive-free conditions furnish a variety of substituted 2-aminobenzoxazoles in moderate to excellent yields. A series of control experiments and spectroscopic studies point to the importance of 2-aminophenol coordination in enabling the aerobic oxidation of cobalt(II).

Nickel-Catalyzed Oxidative Decarboxylative Annulation for the Synthesis of Heterocycle-Containing Phenanthridinones.

A nickel-catalyzed oxidative decarboxylative annulation reaction of simple benzamides and (hetero)aromatic carboxylates has been developed. This reaction provides access to a large array of phenanthridinones and their heterocyclic analogues, highlighting the utility and versatility of oxidative decarboxylative coupling strategies for C-C bond formation.

A Predictive Model for the Decarboxylation of Silver Benzoate Complexes Relevant to Decarboxylative Coupling Reactions.

Decarboxylative coupling reactions offer an attractive route to generate functionalized arenes from simple and readily available carboxylic acid coupling partners, yet they are underutilized due to limitations in the scope of carboxylic acid coupling partner. Here we report that the field effect parameter (F) has a substantial influence on the rate of decarboxylation of well-defined silver benzoate complexes. This finding provides the opportunity to surpass current substrate limitations associated with decarboxylation and to enable widespread utilization of decarboxylative coupling reactions.

Silver-Mediated Oxidative Decarboxylative Trifluoromethylthiolation of Coumarin-3-carboxylic Acids.

The introduction of trifluoromethylthio groups into organic compounds, in particular heterocycles, is important because of the prevalence of these structures in medicinally and agriculturally relevant molecules. Herein, the silver-mediated oxidative decarboxylative trifluoromethylthiolation of coumarin-3-carboxylic acids is reported. This methodology utilizes existing carboxylic acid functionalities for the direct conversion to CFS groups and results in a broad scope of 3-trifluoromethylthiolated coumarins, including analogues of natural products, in moderate to excellent yields.

Aerobic copper-catalyzed decarboxylative thiolation.

Copper-catalyzed decarboxylative thiolation using molecular oxygen as the sole oxidant was developed. A variety of aromatic carboxylic acids including 2-nitrobenzoic acids, pentafluorobenzoic acid and several heteroaromatic carboxylic acids undergo efficient thiolation to furnish the aryl sulfides in moderate to excellent yields.

Copper-catalyzed oxidative decarboxylative C-H arylation of benzoxazoles with 2-nitrobenzoic acids.

A copper-catalyzed oxidative decarboxylative coupling of benzoxazoles with 2-nitrobenzoic acids was developed. This methodology favors electron-rich benzoxazoles and electron-deficient benzoic acids and enables the preparation of a variety of arylated benzoxazoles in good yields. The trends in product yields suggest a delicate balance between the decarboxylation and C-H arylation steps.

Copper/TEMPO-Catalyzed Aerobic Alcohol Oxidation: Mechanistic Assessment of Different Catalyst Systems.

Combinations of homogeneous Cu salts and TEMPO have emerged as practical and efficient catalysts for the aerobic oxidation of alcohols. Several closely related catalyst systems have been reported, which differ in the identity of the solvent, the presence of 2,2'-bipyridine as a ligand, the identity of basic additives, and the oxidation state of the Cu source. These changes have a significant influence on the reaction rates, yields, and substrate scope.

Mechanism of copper(I)/TEMPO-catalyzed aerobic alcohol oxidation.

Homogeneous Cu/TEMPO catalyst systems (TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxyl) have emerged as some of the most versatile and practical catalysts for aerobic alcohol oxidation. Recently, we disclosed a (bpy)Cu(I)/TEMPO/NMI catalyst system (NMI = N-methylimidazole) that exhibits fast rates and high selectivities, even with unactivated aliphatic alcohols. Here, we present a mechanistic investigation of this catalyst system, in which we compare the reactivity of benzylic and aliphatic alcohols.

Copper(I)/TEMPO-catalyzed aerobic oxidation of primary alcohols to aldehydes with ambient air.

This protocol describes a practical laboratory-scale method for aerobic oxidation of primary alcohols to aldehydes, using a chemoselective Cu(I)/TEMPO (TEMPO = 2,2,6,6-tetramethyl-1-piperidinyloxyl) catalyst system. The catalyst is prepared in situ from commercially available reagents, and the reactions are performed in a common organic solvent (acetonitrile) with ambient air as the oxidant. Three different reaction conditions and three procedures for the isolation and purification of the aldehyde product are presented.

Highly practical copper(I)/TEMPO catalyst system for chemoselective aerobic oxidation of primary alcohols.

Aerobic oxidation reactions have been the focus of considerable attention, but their use in mainstream organic chemistry has been constrained by limitations in their synthetic scope and by practical factors, such as the use of pure O(2) as the oxidant or complex catalyst synthesis. Here, we report a new (bpy)Cu(I)/TEMPO catalyst system that enables efficient and selective aerobic oxidation of a broad range of primary alcohols, including allylic, benzylic, and aliphatic derivatives, to the corresponding aldehydes using readily available reagents, at room temperature with ambient air as the oxidant. The catalyst system is compatible with a wide range of functional groups and the high selectivity for 1° alcohols enables selective oxidation of diols that lack protecting groups.

Platinum-catalyzed intramolecular hydrohydrazination: evidence for alkene insertion into a Pt-N bond.

Dicationic (bpy)Pt(II) complexes were found to catalyze the intramolecular hydrohydrazination of alkenes. Reaction optimization revealed Pt(bpy)Cl(2) (10 mol %) and AgOTf (20 mol %) in DMF-d(7) to be an effective catalyst system for the conversion of substituted hydrazides to five- and six-membered N-amino lactams (N-amino = N-acetamido at 120 degrees C, N-phthalimido at 80 degrees C, (-)OTf = trifluoromethanesulfonate). Of the four possible regioisomeric products, only the product of 5-exo cyclization at the proximal nitrogen is formed, without reaction at the distal nitrogen or 6-endo cyclization.