Aminocyanation by the Addition of N–CN Bonds to Arynes: Chemoselective Synthesis of 1,2-Bifunctional Aminobenzonitriles

An efficient aminocyanation by the direct addition of aryl cyanamides to arynes is described, enabling incorporation of highly useful amino and cyano groups synchronously via cleavage of inert N–CN bonds, affording synthetically useful 1,2-bifunctional aminobenzonitriles. The postsynthetic functionalization of the aminocyanation products allows diverse formation of synthetically important derivatives such as drug molecule Ponstan and fused heterocycles

Synthesis of 2‑Benzylphenyl Ketones by Aryne Insertion into Unactivated C–C Bonds

A transition-metal-free procedure to access to functionalized 2-benzylphenyl ketones is described by direct insertion of arynes into benzylic C–C bonds. This reaction was promoted by cesium fluoride at room temperature, allowing the products to form in high selectivity and achieve good functional group tolerance

Metal-Free Regio- and Chemoselective Hydroboration of Pyridines Catalyzed by 1,3,2-Diazaphosphenium Triflate

N-Heterocyclic phosphenium triflates (NHP-OTf) <b>1</b> serve as efficient catalysts for the regio- and chemoselective hydroboration of pyridines under ambient condition with good functional group tolerance. Mechanistic studies indicate that a boronium salt, [(Py)₂·Bpin]­OTf <b>4</b>, is generated concomitant with NHP-H <b>5</b> via hydride abstraction from HBpin by <b>1</b> in the initial reaction step. Hydride reduction of the activated pyridine in [(Py)₂·Bpin]­OTf <b>4</b> by NHP-H <b>5</b> affords the 1,4-hydroboration product selectively. Thus, the phosphenium species act as a hydrogen transfer reagent in the catalytic cycle

Synthesis of 2‑Benzylphenyl Ketones by Aryne Insertion into Unactivated C–C Bonds

A transition-metal-free procedure to access to functionalized 2-benzylphenyl ketones is described by direct insertion of arynes into benzylic C–C bonds. This reaction was promoted by cesium fluoride at room temperature, allowing the products to form in high selectivity and achieve good functional group tolerance

Metal-Free Catalytic Reduction of α,β-Unsaturated Esters by 1,3,2-Diazaphospholene and Subsequent C–C Coupling with Nitriles

1,3,2-Diazaphospholene <b>1</b> catalyzes the conjugate transfer hydrogenation as well as the 1,4-hydroboration of α,β-unsaturated esters. The initial step for both processes involves a 1,4-hydrophosphination of the α,β-unsaturated esters to afford a phosphinyl enol ether. Subsequent cleavage of the P–O bond in the phosphinyl enol ether by ammonia-borane (<b>AB</b>) generates an enol intermediate which tautomerizes to saturated esters, while the P–O bond cleavage by HBpin via a formal σ-bond metathesis affords boryl enolate intermediate. The latter could undergo a further coupling reaction with nitriles to form substituted amino diesters or 1,3-imino esters, depending on α,β-unsaturated ester substrates. These catalytic reactions can also be performed in a one-pot manner, illustrating a protocol for metal-free catalytic C–C bond construction

Highly Selective Hydrogenation of Aromatic Ketones and Phenols Enabled by Cyclic (Amino)(alkyl)carbene Rhodium Complexes

Air-stable Rh complexes ligated by strongly σ-donating cyclic (amino)­(alkyl)­carbenes (CAACs) show unique catalytic activity for the selective hydrogenation of aromatic ketones and phenols by reducing the aryl groups. The use of CAAC ligands is essential for achieving high selectivity and conversion. This method is characterized by its good compatibility with unsaturated ketones, esters, carboxylic acids, amides, and amino acids and is scalable without detriment to its efficiency

Iron-Catalyzed <i>N</i>‑Arylsulfonamide Formation through Directly Using Nitroarenes as Nitrogen Sources

One-step, catalytic synthesis of <i>N</i>-arylsulfonamides via the construction of N–S bonds from the direct coupling of sodium arylsulfinates with nitroarenes was realized in the presence of FeCl₂ and NaHSO₃ under mild conditions. In this process, stable and readily available nitroarenes were used as nitrogen sources, and NaHSO₃ acted as a reductant to provide <i>N</i>-arylsulfonamides in good to excellent yields. A broad range of functional groups were very well-tolerated in this reaction system. In addition, mechanistic studies indicated that the N–S bond might be generated through direct coupling of nitroarene with sodium arylsulfinate prior to the reduction of nitroarenes by NaHSO₃. Accordingly, a reaction mechanism involving <i>N</i>-aryl-<i>N</i>-arenesulfonylhydroxylamine as an intermediate was proposed

Bis(N-heterocyclic olefin) Derivative: An Efficient Precursor for Isophosphindolylium Species

We have developed bis­(N-heterocyclic olefin) derivatives <b>2</b> and demonstrated that <b>2</b> can be utilized as precursors for the synthesis of isophosphindolylium species <b>3</b>. X-ray diffraction and density functional theory studies indicate the aromatic property of the PC₄ five-membered ring in <b>3</b>. Despite its cationic nature, the P center in <b>3b</b> exhibits nucleophilic character and thus readily forms a bond with CuCl to afford a copper phosphenium complex <b>4</b>, demonstrating the potential utility of <b>3</b> as a σ-donor ligand

Pd(II)-Catalyzed Intermolecular Arylation of Unactivated C(sp³)–H Bonds with Aryl Bromides Enabled by 8‑Aminoquinoline Auxiliary

An example of using readily available, less reactive aryl bromides as arylating reagents in the Pd­(II)-catalyzed intermolecular arylation of unactivated C­(sp³)–H bonds is described. This reaction was promoted by a crucial 8-aminoquinolinyl directing group and a K₂CO₃ base, enabling regiospecific installation of an aryl scaffold at the β-position of carboxamides. A mechanistic study by DFT calculations reveals a C­(sp³)–H activation-led pathway featuring the oxidative addition as the highest energy transition state

Media 1: Optical-resolution photoacoustic endomicroscopy in vivo

Originally published in Biomedical Optics Express on 01 March 2015 (boe-6-3-918