Hyunwoo Kim

We describe a new electrophotocatalytic strategy that harnesses the power of light and electricity to generate an excited radical anion with a reducing potential of -3.2 V vs SCE, which can be used to activate substrates with very high reduction potentials (<i>E</i>_red ≈ -1.9 to -2.9 V). The resultant aryl radicals can be engaged in various synthetically useful transformations to furnish arylboronate, arylstannane, and biaryl products.

Cross-dehydrogenative couplings (CDCs) have become one of the most straightforward protocols in the C–H bond functionalizations, showing step- and atom-efficiency without need of prefunctionalization of substrates and reactants. However, catalytic C–H amination procedures based on the CDC strategy by employing amine reactants are considered to be challenging mainly due to the highly nucleophilic character of parent amines to inhibit the catalytic turnovers and the difficulty in optimizing proper

Described herein is the development of an iridium-catalyzed direct C-H amination of benzamides with anilines at room temperature, representing a unique example of an Ir catalyst system that is compatible with external oxidants. Mechanistic details, such as the isolation and characterization of key iridacycle intermediates, are also discussed.

[Structure: see text] A new mechanism involving a diimine intermediate is proposed for vicinal diamine-catalyzed synthesis of warfarin. Decreasing the NCCN dihedral angle by varying the diamine results in an increase in the enantioselectivity of warfarin synthesis.

The direct amination of C-H bonds with ammonia is a challenge in synthetic chemistry. Herein, we present a copper-mediated approach that enables a chelation-assisted aromatic C-H bond amination using aqueous ammonia. A key strategy was to use soft low-valent Cu(I) species to avoid the strong coordination of ammonia. Mechanistic investigations suggest that the catalysis is initiated by a facile deprotonation of bound ammonia, and the C-N coupling is achieved by subsequent reductive elimination of

The development of efficient and elective transition metal catalyst systems enabling a direct C-H amination of hydrocarbons using ammonia is highly desirable considering the fact that ammonia is the most readily available nitrogen source. It is anticipated that a new mechanistic scaffold distinct from the currently applicable ones will guide this research eventually to have broad applicability in synthetic methodology, medicinal chemistry, and materials science.

Described herein is the development of Ir(III)-catalyzed direct C–H amidation using azidoformates as a readily deprotectable amino source. Substrates with unactivated methyl C(sp3)–H and aromatic or olefinic C(sp2)–H bonds were smoothly reacted by the iridium-based catalyst system to provide the corresponding primary alkylamines and anilines upon the subsequent removal of N-protecting groups, such as Boc, Fmoc, Cbz, pNZ, or Troc. A brief mechanistic study and synthetic applications are also pres

A new synthetic route to phosphoramidates by intermolecular C-H amidation is presented. Substrates with assorted directing groups were activated by an iridium-based catalyst system and reacted with a number of phosphoryl azides, executing efficient phosphoramidate synthesis via C-N bond formations.

Described herein is the development of Cp*Ir(III)-catalyzed direct arene C–H amination using alkylamines as an amino source. This C–N bond formation showcases a notable example of cross-dehydrogenative coupling to install an amino functionality at the ortho-position of benzamide substrates. Mechanistic studies including the isolation of an amine-bound iridacyclic intermediate along with a set of chemical oxidations demonstrated the Ir-catalyzed inner-sphere C–H amination with primary alkylamines

Direct transamidation of secondary amides was developed via nickel catalysis. In the presence of trimethylsilyl chloride and manganese, Ni(diglyme)Cl₂ with a Briphos ligand efficiently promoted the transamidation of N-aryl benzamide derivatives with primary amines to afford the corresponding secondary amides in moderate to good yields. Primary amines bearing electron-donating groups gave higher yields of the transamidation products.

We have demonstrated the efficient chiral analysis of fluorine-containing compounds by ¹⁹F NMR spectroscopy. The highly sensitive fluorine nucleus allowed chiral analysis of complex mixtures and even asymmetric reaction mixtures of multisubstrates. A single ¹⁹F NMR experiment was sufficient to determine the enantiomeric excesses and yields of the five products simultaneously.

Controlled oxidation of palladium nanoparticles provided high-valent Pd^IV oxo-clusters which efficiently promote directed C-H halogenation reactions. In addition, palladium nanoparticles can undergo changes in oxidation states to provide both high-valent Pd^IV and low-valent Pd⁰ species within one system, and thus a tandem reaction of C-H halogenation and cross-coupling (C-N, C-C, and C-S bond formation) was successfully established.

Alternating current electrolysis (ACE) is an emerging powerful synthetic tool, which principally resembles photoredox catalysis strategies. Its periodically alternating polarity feature allows oxidation and reduction processes to take place on the same electrode surface in a well-controlled manner via the fine-tuning of current frequency along with other reaction parameters. Therefore, many challenging transformations in typical direct electrolysis, including constant current electrolysis or con

The determination of the enantiomeric excess and absolute configuration of chiral compounds is indispensable in synthetic, pharmaceutical, and biological chemistry. In this article, we describe an efficient ¹⁹F nuclear magnetic resonance (NMR)-based analytical protocol for determining the enantiomeric excess and absolute configuration of <i>in situ</i> fluorine-labeled amines and alcohols. 2-Fluorobenzoylation was used to convert analytes to fluorinated amides or esters. The resulting

The Pd(iv) species, known to be critical intermediates in homogeneous catalysis, were successfully generated on the surface of Pd nanocatalysts via oxidation with iodobenzene dichloride (PhICl2) or N-chlorosuccinimide (NCS). In particular, the Pd@SiO2 yolk-shell nanocatalyst activated by PhICl2 showed high reactivity and superior stability to the other Pd-based catalysts for hydroalkoxylation reactions even at 25 °C.