Soon Hyeok Hong

Direct Amide Synthesis from Either Alcohols or Aldehydes with Amines: Activity of Ru(II) Hydride and Ru(0) Complexes

An in situ generated catalyst from readily available RuH(2)(PPh(3))(4), an N-heterocyclic carbene (NHC) precursor, NaH, and acetonitrile was developed. The catalyst showed high activity for the amide synthesis directly from either alcohols or aldehydes with amines. When a mixture of an alcohol and an aldehyde was reacted with an amine, both of the corresponding amides were obtained with good yields. Homogeneous Ru(0) complexes such as (eta(4)-1,5-cyclooctadiene)(eta(6)-1,3,5-cyclooctatriene)ruthenium [Ru(cod)(cot)] and Ru(3)(CO)(12) were also active in the amidation of an alcohol or an aldehyde with the help of an in situ generated NHC ligand.

Ruthenium-catalyzed redox-neutral and single-step amide synthesis from alcohol and nitrile with complete atom economy.

A completely atom-economical and redox-neutral catalytic amide synthesis from an alcohol and a nitrile is realized. The amide C-N bond is efficiently formed between the nitrogen atom of nitrile and the α-carbon of alcohol, with the help of an N-heterocyclic carbene-based ruthenium catalyst, without a single byproduct. A utility of the reaction was demonstrated by synthesizing (13)C or (15)N isotope-labeled amides without involvement of any separate reduction and oxidation step.

N-heterocyclic carbene based ruthenium-catalyzed direct amide synthesis from alcohols and secondary amines: involvement of esters.

A well-defined N-heterocyclic carbene based ruthenium complex was developed as a highly active precatalyst for the direct amide synthesis from alcohols and secondary amines. Notably, reaction of 1-hexanol and dibenzylamine afforded 60% of the corresponding amide using our catalytic system, while no amide formation was observed for this reaction with the previously reported catalytic systems. Unlike the previously reported amidation with less sterically hindered alcohols and amines, involvement of ester intermediates was observed.

Low Catalyst Loadings in Olefin Metathesis: Synthesis of Nitrogen Heterocycles by Ring Closing Metathesis

A series of ruthenium catalysts have been screened under ring-closing metathesis (RCM) conditions to produce five-, six-, and seven-membered carbamate-protected cyclic amines. Many of these catalysts demonstrated excellent RCM activity and yields with as low as 500 ppm catalyst loadings. RCM of the five-membered carbamate series could be run neat, the six-membered carbamate series could be run at 1.0 M, and the seven-membered carbamate series worked best at 0.2-0.05 M.

Ruthenium-Catalyzed Urea Synthesis Using Methanol as the C1 Source

An unprecedented protocol for urea synthesis directly from methanol and amine was accomplished. The reaction is highly atom-economical, producing hydrogen as the sole byproduct. Commercially available ruthenium pincer complexes were used as catalysts. In addition, no additive, such as a base, oxidant, or hydrogen acceptor, was required. Furthermore, unsymmetrical urea derivatives were successfully obtained via a one-pot, two-step reaction.

Dehydrogenative Amide Synthesis: Azide as a Nitrogen Source

A new atom-economical strategy to amide linkage from an azide and alcohol liberating hydrogen and nitrogen was developed with an in situ generated ruthenium catalytic system. The reaction has broad substrate generality including diols for the synthesis of cyclic imides.

Tandem insertion-cyclization reaction of isocyanides in the synthesis of 1,4-diaryl-1H-imidazoles: presence of N-arylformimidate intermediate.

A straightforward and high-yielding synthesis of 1,4-diaryl-1H-imidazoles is reported. 1,4-Diaryl-1H-imidazoles have been difficult to access in ambient conditions, but our method utilizes two different facets of isocyanide reactivity to achieve it. The reaction is believed to involve (1) NHC-copper-catalyzed isocyanide insertion into alcohol to form an N-arylformimidate intermediate and (2) subsequent base-promoted cycloaddition with benzyl isocyanide derivatives. There is cooperation between these two processes through the deprotonation of benzyl isocyanide by KOtBu. The deprotonation gives tert-butyl alcohol and the benzyl isocyanide anion, which are used for the first and second steps of the reaction, respectively. Various control and kinetic experiments were carried out to gain an in-depth understanding of the reaction mechanism and isocyanide reactivity. The reaction mechanism determined by density functional theory calculations was consistent with the experimental data and provided detailed explanations for the reactivity trends.

Selective catalytic sp3 C–O bond cleavage with C–N bond formation in 3-alkoxy-1-propanols

The ruthenium catalyzed selective sp(3) C-O cleavage with amide formation was reported in reactions of 3-alkoxy-1-propanol derivatives and amines. The cleavage only occurs at the C3-O position even with 3-benzyloxy-1-propanol. Based on the experimental results, O-bound and C-bound Ru enolate complexes were proposed as key intermediates for the unique selective sp(3) C-O bond cleavage in 3-alkoxy-1-propanols.

CH-π and CF-π interactions lead to structural changes of N-heterocyclic carbene palladium complexes

The role of CH-π and CF-π interactions in determining the structure of N-heterocyclic carbene (NHC) palladium complexes were studied using (1) H NMR spectroscopy, X-ray crystallography, and DFT calculations. The CH-π interactions led to the formation of the cis-anti isomers in 1-aryl-3-isopropylimidazol-2-ylidene-based [(NHC)2 PdX2 ] complexes, while CF-π interactions led to the exclusive formation of the cis-syn isomer of diiodobis(3-isopropyl-1-pentafluorophenylimidazol-2-ylidene) palladium(II).

Synthesis of Cyclic Imides from Nitriles and Diols Using Hydrogen Transfer as a Substrate-Activating Strategy

An atom-economical and versatile method for the synthesis of cyclic imides from nitriles and diols was developed. The method utilizes a Ru-catalyzed transfer-hydrogenation reaction in which the substrates, diols, and nitriles are simultaneously activated into lactones and amines in a redox-neutral manner to afford the corresponding cyclic imides with evolution of H2 gas as the sole byproduct. This operationally simple and catalytic synthetic method provides a sustainable and easily accessible route to cyclic imides.