Copper-Catalyzed Hiyama Coupling of (Hetero)aryltriethoxysilanes with (Hetero)aryl Iodides

A Cu^I-catalyzed Hiyama coupling was achieved, which proceeds in the absence of an ancillary ligand for aryl–heteroaryl and heteroaryl–heteroaryl couplings. A P,N-ligand is required to obtain the best product yields for aryl–aryl couplings. In addition to facilitating transmetalation, CsF is also found to function as a stabilizer of the [CuAr] species, potentially generated as an intermediate after transmetalation of aryltriethoxysilanes with Cu^I-catalysts in the absence of ancillary ligands

Catalytic Photoredox Carbobromination of Unactivated Alkenes with α‑Bromocarbonyls via the Mechanistically Distinct Radical-Addition Radical-Pairing Pathway

We disclose a catalytic photoredox carbobromination of unactivated alkenes with α-bromocarbonyl compounds under blue-light-emitting diode (LED) light. The reaction proceeds with α-bromoesters, α-bromonitriles, and α-bromo-γ-lactones along with terminal and 1,2-disubstituted internal alkenes. Reactions with indenes and 1,1-disubstituted alkenes generate alkylated alkenes. Mechanistic studies by product selectivity and three-way competitive crossover experiments suggest that the reaction operates by a radical-addition radical-pairing (RARP) mechanism. The catalytic turnover is achieved by a single electron reduction of PC•+ by Br– (or Br3–), rather than by the alkyl radical (R•), and the product is generated by the pairing of Br• (or Br2•–) and R•, instead of the combination of Br– and a carbocation (R+)

Iron-Mediated Dialkylation of Alkenylarenes with Benzyl Bromides

We disclose a method for the dibenzylation of alkenylarenes with benzyl bromides using iron powder. This reaction generates branched alkyl scaffolds adorned with functionalized aryl rings through the formation of two new C(sp3)–C(sp3) bonds at the vicinal carbons of alkenes. This protocol tolerates electron-rich, electron-neutral, and electron-poor benzyl bromides and alkenylarenes. Mechanistic studies suggest the formation of benzylic radical intermediates as a result of single-electron transfer from the iron, which is intercepted by alkenylarenes

Fully Synthetic Approach toward Transition Metal–Nitrogen–Carbon Oxygen Reduction Electrocatalysts

We report a nonpyrolytic chemical synthesis of model iron–nitrogen–carbon electrocatalysts for oxygen reduction reaction (ORR) to elucidate the role of Fe–N centers in the catalysis mechanism. The graphene-supported and unsupported catalysts were analyzed in detail by X-ray spectroscopy techniques. The electrochemical analysis was performed by linear sweep voltammetry and square wave voltammetry in 0.5 M H₂SO₄ and 0.1 M KOH electrolytes. In this article, with the use of model catalysts, we manifest and confirm the difference in the specific role of Fe–N active sites toward ORR in acidic and alkaline environments

Ni-Catalyzed Regioselective Dicarbofunctionalization of Unactivated Olefins by Tandem Cyclization/Cross-Coupling and Application to the Concise Synthesis of Lignan Natural Products

We disclose a (terpy)­NiBr₂-catalyzed reaction protocol that regioselectively difunctionalizes unactivated olefins with tethered alkyl halides and arylzinc reagents. The reaction shows an excellent functional group tolerance (such as ketones, esters, nitriles, and halides) and a moderate to good level of diastereoselectivity. The current cyclization/cross-coupling also tolerates molecules containing base-sensitive racemizable stereocenters, which are preserved without racemization during the reaction. This cyclization/cross-coupling provides a rapid access to (arylmethyl)­carbo- and heterocyclic scaffolds, which occur widely as structural cores in various natural products and bioactive molecules. In order to show synthetic utility and generality, we have applied this new method in gram-scale quantities to the concise synthesis of six lignan natural products containing three different structural frameworks. We further conducted mechanistic investigations with radical probes and selectivity studies, which indicated that the current reaction proceeds via a single electron transfer (SET) process

Site-Selective C(sp³)–H Functionalization of Di‑, Tri‑, and Tetrapeptides at the N‑Terminus

Although the syntheses of novel and diverse peptides rely mainly on traditional coupling using unnatural amino acids, postsynthetic modification of peptides could provide a complementary method for the preparation of nonproteinogenic peptides. Site selectivity of postsynthetic modification of peptides is usually achieved by targeting reactive moieties, such as the thiol group of cysteine or the C-2 position of tryptophan. Herein, we report the development of site-selective functionalizations of inert C­(sp³)–H bonds of N-terminal amino acids in di-, tri-, and tetrapeptides without installing a directing group. The native amino acid moiety within the peptide is used as a ligand to accelerate the C–H activation reaction. In the long run, this newly uncovered reactivity could provide guidance for developing site-selective C­(sp³)–H activation toward postsynthetic modification of a broader range of peptides

Copper-Catalyzed Suzuki–Miyaura Coupling of Arylboronate Esters: Transmetalation with (PN)CuF and Identification of Intermediates

An efficient Cu^I-catalyzed Suzuki–Miyaura reaction was developed for the coupling of aryl- and heteroarylboronate esters with aryl and heteroaryl iodides at low catalyst loadings (2 mol %). The reaction proceeds under ligand-free conditions for aryl–heteroaryl and heteroaryl–heteroaryl couplings. We also conducted the first detailed mechanistic studies by synthesizing [(<b>PN-2</b>)­CuI]₂, [(<b>PN-2</b>)­CuF]₂, and (<b>PN-2</b>)­CuPh (<b>PN-2</b> = <i>o</i>-(di-<i>tert</i>-butylphosphino)-<i>N</i>,<i>N</i>-dimethylaniline) and demonstrated that [(<b>PN-2</b>)­CuF]₂ is the species that undergoes transmetalation with arylboronate esters