Copper-Catalyzed Innate Ethoxycarbon­yldifluoromethylation of Electron-Rich ­Arenes

Copper-Photocatalyzed Hydroboration of Alkynes and Alkenes

The photocatalytic hydroboration of alkenes and alkynes is reported. The use of newly-designed copper photocatalysts with B2 Pin2 permits the formation a boryl radical, which is used for hydroboration of a large panel of alkenes and alkynes. The hydroborated products were isolated in high yields, with excellent diastereoselectivities and a high functional group tolerance under mild conditions. The hydroboration reactions were developed under continuous flow conditions to demonstrate their synthetic utility. The reaction mechanism was studied and suggested an oxidation reaction between an in situ formed borate and the Cu-photocatalyst in its excited state for the boryl radical formation.

Iron-Catalyzed Highly para-Selective Difluoromethylation of Arenes

Direct functionalization of a C-H bond at either the meta or para position by only changing the catalyst system poses a significant challenge. We herein report the [Fe(TPP)Cl]-enabled, selective, C-H difluoromethylation of arenes using BrCF₂CO₂Et as the difluoromethylation source, which successfully altered the selectivity from the meta to the para position. A preliminary mechanistic study revealed the iron porphyrin complex not only activated the aromatic ring but also induced para selectivity due to the influence of ligand sterics.

Visible-Light-Induced para-Selective C(sp2)-H Difluoroalkylation of Diverse (Hetero)aromatic Carbonyls

An efficient visible-light-induced para-selective C(sp²)-H difluoroalkylation of diverse electron-deficient (hetero)aromatic carbonyls (aldehydes and ketones) at ambient temperature has been developed by employing Ir(ppy)₃ as the catalyst and 1,10-phenanthroline as the additive. This protocol was highlighted by its wide substrate scope, high regioselectivity, low catalyst usage, and operational simplicity.

Copper-Catalyzed Enantioselective Formation of C-CF3 Centers from β-CF3 -Substituted Acrylates and Acrylonitriles

The catalytic asymmetric synthesis of β-trifluoromethylated esters or nitriles is reported. The use of an in situ formed chiral Cu-H complex allowed the enantioselective reduction of β-trifluoromethylated acrylates or acrylonitriles. The reaction proceeds smoothly affording the corresponding enantioenriched products in good to excellent yields and outstanding enantioselectivities (up to 98 % ee). The mechanism of the reaction was studied, and a plausible reaction pathway was suggested accordingly. Finally, the versatility of the products was highlighted through functional group manipulations.

Copper-Photocatalyzed Borylation of Organic Halides under Batch and Continuous-Flow Conditions

The copper-photocatalyzed borylation of aryl, heteroaryl, vinyl and alkyl halides (I and Br) was reported. The reaction proceeded using a new heteroleptic Cu complex under irradiation with blue LEDs, giving the corresponding boronic-acid esters in good to excellent yields. The reaction was extended to continuous-flow conditions to allow an easy scale-up. The mechanism of the reaction was studied and a mechanism based on a reductive quenching (Cu^I /Cu^I */Cu⁰ ) was suggested.

3d Transition Metals for C-H Activation

C-H activation has surfaced as an increasingly powerful tool for molecular sciences, with notable applications to material sciences, crop protection, drug discovery, and pharmaceutical industries, among others. Despite major advances, the vast majority of these C-H functionalizations required precious 4d or 5d transition metal catalysts. Given the cost-effective and sustainable nature of earth-abundant first row transition metals, the development of less toxic, inexpensive 3d metal catalysts for C-H activation has gained considerable recent momentum as a significantly more environmentally-benign and economically-attractive alternative. Herein, we provide a comprehensive overview on first row transition metal catalysts for C-H activation until summer 2018.

A Ligand-Enabled Palladium-Catalyzed Highly para-Selective Difluoromethylation of Aromatic Ketones

A practical and highly para-selective C-H difluoromethylation of aromatic ketones has been developed by employing tetrakis(triphenylphosphine)palladium(0) as the catalyst and triphenylphosphine as the ligand. In addition to general aromatic ketones, this transformation was compatible with bioactive compounds and well-known drugs, such as oxybenzone, ketoprofen, zaltoprofen, and propafenone. Moreover, a mechanistic study revealed that a palladium intermediate coordinated by a carbonyl group promotes highly para-selective difluoromethylation.

Copper-catalyzed difluoromethylation of propargylamide-substituted indoles: synthesis of mono- and bis-difluoromethylated indoloazepinone derivatives

A novel copper-catalyzed difluoromethylation of 2- or 3-propargylamide-substituted indoles with ICF2CO2Et via a radical cascade cyclization process is described. A wide substrate scope is compatible with the reaction conditions to synthesize mono- and bis-difluoromethylated indoloazepinone derivatives, which contain a seven-membered ring.

Synthesis of 3-CF2-Containing Chromones via a Visible-Light-Induced Radical Cascade Reaction of o-Hydroxyaryl Enaminones

A general and efficient visible-light-induced CF₂ radical-based cascade reaction of o-hydroxyaryl enaminones has been described. This protocol afforded the corresponding functionalized 3-CF₂-containing chromones in generally good yields under mild reaction conditions. The use of NaHSO₃, which has both basicity and reducibility, efficiently suppressed the formation of two byproducts, 4H-chromen-4-one and 3-bromo-4H-chromen-4-one.

Stereoselective access to trisubstituted fluorinated alkenyl thioethers

We report the first copper-catalyzed olefinic ethoxy carbonyl difluoromethylation of alkenyl thioethers via direct C–H bond functionalization using BrCF₂COOEt.

Siladifluoromethylation and Difluoromethylation onto C(sp(3)), C(sp(2)), and C(sp) Centers Using Ruppert-Prakash Reagent and Fluoroform

Siladifluoromethylations and difluoromethylations on sp(3), sp(2), and sp carbons of lithiated carbamates, arenes, and terminal alkynes, respectively, have been attained by employing the Ruppert-Prakash reagent (CF3TMS) and fluoroform (CF3H) as the CF2 sources. The advantage of this reaction is that the (sila)difluoromethylated compounds can be obtained by simple treatment of easily accessible substrates, lithium bases, and CF3TMS or CF3H. Furthermore, the products bearing the TMS group can be transformed into the valuable compounds with the CF2 fragment via the carbon-carbon bond forming reactions.

Copper-catalyzed C–H ethoxycarbonyldifluoromethylation of imidazoheterocycles

A regioselective copper-catalyzed ethoxycarbonyldifluoromethylation of imidazo[1,2-a]pyridines has been developed through sp² C–H bond functionalization with BrCF₂CO₂Et under ambient air.

Palladium-catalyzed C-H ethoxycarbonyldifluoromethylation of electron-rich heteroarenes

The first Pd-catalyzed C-H ethoxycarbonyldifluoromethylation with BrCF2CO2Et has been developed. The use of a bidentate phosphine ligand (Xantphos) is critical for the reaction to occur. A variety of electron-rich heteroarenes, including indoles, furans, thiophenes, and pyrroles, can be ethoxycarbonyldifluoromethylated in moderate to excellent yields. The reactions take place at the C-H bonds adjacent to the heteroatoms with high regioselectivity. This method provides a new protocol for the introduction of difuoroalkyl groups into electron-rich heteroarenes.