A Chemoselective, One-Pot Transformation of Aldehydes to Nitriles

Rhodium(I)-Catalyzed Cascade Annulation of 1,n-Diynyl Nitrones to 3,4-Fused Fully Substituted Furans

A method for the assembly of fully substituted furans containing a 3,4-fused 5-8-membered carbocycle, heterocycle, or spirocycle from rhodium(I)-catalyzed and 1,1,1,3,3,3-hexafluoroisopropanol (HFIP)-assisted cascade annulation of 1,n-diynyl nitrones has been developed.

Diphenylphosphinylhydroxylamine (DPPH) Affords Late-Stage S-imination to access free-NH Sulfilimines and Sulfoximines

Sulfilimines, as potential aza-isosteres of sulfoxides, are valued as building blocks, auxiliaries, ligands, bioconjugation handles, and as precursors to versatile S(VI) scaffolds including sulfoximines and sulfondiimines. Here, we report a thioether imination methodology that exploits O-(diphenylphosphinyl)hydroxyl amine (DPPH). Under mild, metal-free, and biomolecule-compatible conditions, DPPH enables late-stage S-imination on peptides, natural products, and a clinically trialled drug, and shows both excellent chemoselectivity and broad functional group tolerance. This methodological report is extended to an efficient and high-yielding one-pot reaction for accessing free-NH sulfoximines with diverse substrates including ones of potential clinical importance. In the presence of a rhodium catalyst, sulfoxides are S-iminated in higher yields to afford free-NH sulfoximines. S-imination was validated on an oxidatively delicate amatoxin to give sulfilimine and sulfoximine congeners. Interestingly, these new sulfilimine and sulfoximine-amatoxins show cytotoxicity. This method is further extended to create sulfilimine and sulfoximine-Fulvestrant and buthionine analogues.

Introducing a protic ionic liquid from aminoethyl piperazine and triflic acid immobilized on pectin as a reusable nanocatalyst for the selective Schmidt synthesis of nitriles

Preparation of reusable protic ionic liquid, triflic acid-immobilized aminoethyl piperazine-modified pectin (Pec-AEP-TfOH), with excellent activity and selectivity in modified Schmidt synthesis of nitriles from aldehydes and Si(CH3)3N3 has been described. The structure of the catalyst was characterized using FT-IR, XRD, FE-SEM, EDX-mapping, and TGA-DTA. The reaction demonstrated a broad substrate scope for a variety of benzaldehyde derivatives with electron withdrawing/donating substituents and heterocyclic aldehydes with yields between 85 and 96 % at room temperature. Also, the Pec-AEP-TfOH showed an excellent selectivity for the nitriles in which no formanilide was obtained. Furthermore, the Pec-AEP-TfOH revealed a remarkable chemoselectivity for aldehydes in the presence of acids or ketones. It is worth noting that TfOH as a precious superacid was immobilized for the first time in the selective Schmidt synthesis of nitriles to improve the eco-friendliness and economic efficiency of the process. Furthermore, the catalyst was cost-effective, metal-free, safe, scalable, and reusable (5 times) and its heterogeneity was confirmed by hot-filtration test.

From Cycloalkanols to Heterocycles via Nitrogen Insertion

A variety of cyclic alcohols are found to undergo nitrogen insertion by subjection to O-mesitylsulfonylhydroxylamine. Critical to a successful process is the use of fluorinated alcoholic solvents, which ensures sufficient substrate activation to allow engagement with the ambiphilic aminating agent. This transition-metal-free nitrogen insertion provides access to a variety of medicinally relevant heterocycles such as pyrrolidenes, quinolines, and benzazepines (24 examples). Furthermore, combination with a photochemical Norrish-Yang-type cyclization allows an unprecedented access to indoles from ortho-substituted acetophenones.

Oxygen transfer reaction of haloalkyl amides catalyzed by phenylboronic acid

Nitrile derivatives are important building blocks in organic synthesis. Herein, we report the serendipitous discovery of an oxygen transfer reaction that produces hydroxyalkyl nitriles from the sequential dehydration and hydrolysis of haloalkyl amides. Product yields of up to 91% were achieved, and the phenylboronic acid was recovered as triphenylboroxine. The triphenylboroxine was reused as a catalyst without any loss of catalytic activity. A probable catalytic pathway was proposed based on control experiments and DFT calculations.

Aryl acrylonitriles synthesis enabled by palladium-catalyzed α-alkenylation of arylacetonitriles with vinyl halides/triflates

Aryl acrylonitriles are an important subclass of acrylonitriles in the medicinal chemistry and pharmaceutical industry. Herein, an efficient synthesis of aryl acrylonitrile derivatives using a Palladium/NIXANTPHOS-based catalyst system was developed. This approach furnishes a variety of substituted and functionalized aryl acrylonitriles (up to 95% yield). The scalability of the transformation and the synthetic versatility of aryl acrylonitrile were demonstrated.

Divergent Total Syntheses of Napelline-Type C20-Diterpenoid Alkaloids: (-)-Napelline, (+)-Dehydronapelline, (-)-Songorine, (-)-Songoramine, (-)-Acoapetaldine D, and (-)-Liangshanone

The napelline-type alkaloids possess an azabicyclo[3.2.1]octane moiety and an ent-kaurane-type tetracyclic skeleton (6/6/6/5) along with varied oxidation patterns embedded in the compact hexacyclic framework. Herein, we disclose a divergent entry to napelline-type alkaloids that hinges on convergent assembly of the ent-kaurane core using a diastereoselective intermolecular Cu-mediated conjugate addition and subsequent intramolecular Michael addition reaction as well as rapid construction of the azabicyclo[3.2.1]octane motif via an intramolecular Mannich cyclization. The power of this strategy has been demonstrated through efficient asymmetric total syntheses of eight napelline-type alkaloids, including (-)-napelline, (-)-12-epi-napelline, (+)-dehydronapelline, (+)-12-epi-dehydronapelline, (-)-songorine, (-)-songoramine, (-)-acoapetaldine D, and (-)-liangshanone.

Momentary Clicking Nitrile Synthesis Enabled by an Aminoazanium Reagent

Achieving fast and selective functional group interconversion is crucial for improving synthetic efficiency in nowadays chemical science. In this context, we report a momentary and selective Schmidt-type nitrile synthesis. The...

Copper-Catalyzed One-Pot Synthesis of Quinazolinones from 2-Nitrobenzaldehydes with Aldehydes: Application toward the Synthesis of Natural Products

A novel, efficient, and atom-economical approach for the construction of quinazolinones from 2-nitrobenzaldehydes has been unveiled via copper-catalyzed nitrile formation, hydrolysis, and reduction in one pot for the first time. In this reaction, urea is used as a source of nitrogen for nitrile formation, hydrazine hydrate is used for both the reduction of the nitro group and the hydrolysis of nitrile, and atmospheric oxygen is used as the sole oxidant. The method portrays a wide substrate scope with good functional group tolerances. Moreover, this method was applied for the synthesis of schizocommunin, tryptanthrin, phaitanthrin-A, phaitanthrin-B, and 8H-quinazolino[4,3-b]quinazolin-8-one.

Transformation of aldehydes into nitriles in an aqueous medium using O-phenylhydroxylamine as the nitrogen source

The conversion of an aldehyde into a nitrile can be efficiently performed using O-phenylhydroxylamine hydrochloride in buffered aqueous solutions. The reported method is specifically optimized for aqueous-soluble substrates including carbohydrates. Several reducing sugars including monosaccharides, disaccharides, and silyl-protected saccharides were transformed into cyanohydrins in high yields. The reaction conditions are also suitable for the formation of nitriles from various types of hydrophobic aldehyde substrates. Furthermore, cyanide can be eliminated from cyanohydrins, analogous to the Wohl degradation, by utilizing a readily-removed weakly basic resin as a promoter.

On-Demand Generation and Use in Continuous Synthesis of the Ambiphilic Nitrogen Source Chloramine

Herein, we demonstrate the on-demand synthesis of chloramine from aqueous ammonia and sodium hypochlorite solutions, and its subsequent utilization as an ambiphilic nitrogen source in continuous-flow synthesis. Despite its advantages in cost and atom economy, chloramine has not seen widespread use in batch synthesis due to its unstable and hazardous nature. Continuous-flow chemistry, however, provides an excellent platform for generating and handling chloramine in a safe, reliable, and inexpensive manner. Unsaturated aldehydes are converted to valuable aziridines and nitriles, and thioethers are converted to sulfoxides, in moderate to good yields and exceedingly short reaction times. In this telescoped process, chloramine is generated in situ and immediately used, providing safe and efficient conditions for reaction scale-up while mitigating the issue of its decomposition over time.

HCl•DMPU-Assisted One-pot and Metal-free Conversion of Aldehydes to Nitriles

We report an efficient HCl•DMPU assisted one-pot conversion of aldehydes into nitriles. The use of HCl•DMPU as both an acidic source as well as a non-nucleophilic base constitutes an environmentally mild alternative for the preparation of nitriles. Our protocol proceeds smoothly without the use of toxic reagents and metal catalysts. Diverse functionalized aromatic, aliphatic and allylic aldehydes incorporating various functional groups were successfully converted to nitriles in excellent to quantitative yields. This protocol is characterized by a broad substrate scope, mild reaction conditions, and high scalability.

Cascade Process for Direct Transformation of Aldehydes (RCHO) to Nitriles (RCN) Using Inorganic Reagents NH2OH/Na2CO3/SO2F2 in DMSO

A simple, mild, and practical process for direct conversion of aldehydes to nitriles was developed feathering a wide substrate scope and great functional group tolerability (52 examples, over 90% yield in most cases) using inorganic reagents (NH₂OH/Na₂CO₃/SO₂F₂) in DMSO. This method allows for transformations of readily available, inexpensive, and abundant aldehydes to highly valuable nitriles in a pot, atom, and step-economical manner without transition metals. This protocol will serve as a robust tool for the installation of cyano-moieties to complicated molecules.

An effective preparation of both 1,3-diketones and nitriles from alkynones with oximes as hydroxide sources

An effective phosphine-catalyzed protocol has been established for the syntheses of 1,3-diketones and nitriles from alkynones with oximes as hydroxide surrogates. This method features the use of a phosphine catalyst, compatibility with various functional groups and ambient temperature, which makes this approach very practical. A plausible mechanism was proposed.

Applications of sulfuryl fluoride (SO2F2) in chemical transformations

A number of novel methodologies concerning the chemical, biological and medicinal applications of sulfuryl fluoride (SO₂F₂) gas have dramatically improved year by year.

Preparation of oxazolines and oxazoles via a PhI(OAc)2-promoted cyclization of N-propargylamides

A metal-free cyclization of N-propargylamides for the synthesis of various oxazolines and oxazoles via a 5-exo-dig process is presented. Using (diacetoxyiodo)benzene (PIDA) as a reaction promoter and lithium iodide (LiI) as an iodine source, intramolecular iodooxygenation of N-propargylamides proceeded readily, leading to the corresponding (E)-5-iodomethylene-2-oxazolines in good to excellent isolated yields. In addition, using the PhI(OAc)2/LiI system, N-propargylamides can be converted to the corresponding oxazole-5-carbaldehydes in the presence of oxygen under visible light irradiation. The resulting products can be further converted into various oxazoline and oxazole derivatives after simple derivatizations, and this method ultimately offers an efficient route to a variety of biologically active structures.

Ruthenium-Catalyzed Aerobic Oxidation of Amines

Amine oxidation is one of the fundamental reactions in organic synthesis as it leads to a variety of value-added products such as oximes, nitriles, imines, and amides among many others. These products comprise the key N-containing building blocks in the modern chemical industry, and such transformations, when achieved in the presence of molecular oxygen without using stoichiometric oxidants, are much preferred as they circumvent the production of unwanted wastes. In parallel, the versatility of ruthenium catalysts in various oxidative transformations is well-documented. Herein, this review focuses on aerobic oxidation of amines specifically by using ruthenium catalysts and highlights the major achievements in this direction and challenges that still need to be addressed.

Mechanistic Insight Facilitates Discovery of a Mild and Efficient Copper-Catalyzed Dehydration of Primary Amides to Nitriles Using Hydrosilanes

Metal-catalyzed silylative dehydration of primary amides is an economical approach to the synthesis of nitriles. We report a copper-hydride(CuH)-catalyzed process that avoids a typically challenging 1,2-siloxane elimination step, thereby dramatically increasing the rate of the overall transformation relative to alternative metal-catalyzed systems. This new reaction proceeds at ambient temperature, tolerates a variety of metal-, acid-, or base-sensitive functional groups, and can be performed using a simple ligand, inexpensive siloxanes, and low catalyst loading.

O-Substituted hydroxyl amine reagents: an overview of recent synthetic advances

Reagents derived from oxygen-substituted hydroxylamine facilitate stereo- and regioselective C–N, N–N, O–N, and S–N bond-formation reactions and intra-molecular cyclizations without any expensive metal catalysts. These remarkable transformations are discussed in this review.

A practical iodine-catalyzed oxidative conversion of aldehydes to nitriles

A simple and efficient method for the direct synthesis of nitriles from aldehydes using ammonium acetate as the nitrogen source, iodine as the catalyst, and tert-butyl hydroperoxide (TBHP) as the oxidant was developed.

Improved Schmidt Conversion of Aldehydes to Nitriles Using Azidotrimethylsilane in 1,1,1,3,3,3-Hexafluoro-2-propanol

The Schmidt reaction of aromatic aldehydes using a substoichiometric amount (40 mol %) of triflic acid is described. Low catalyst loading was enabled by a strong hydrogen-bond-donating solvent hexafluoro-2-propanol (HFIP). This improved protocol tolerates a broad scope of aldehydes with diverse functional groups and the corresponding nitriles were obtained in good to high yields without the need for aqueous work up.

Cu-catalyzed debrominative cyanation of gem-dibromoolefins: a facile access to α,β-unsaturated nitriles

An efficient catalytic route for the synthesis of α,β-unsaturated nitriles from easily accessible gem-dibromoolefins has been developed. The method utilized inexpensive reagents such as Cu2O as a catalyst, L-proline as a ligand and NaCN as a cyanide source to afford α,β-unsaturated nitriles in high yields (62-86%). A deuterium exchange study has shown that one of the bromide atoms of gem-dibromoolefins exchanges with cyanide while the other with a deuterium atom.

Copper-catalyzed aerobic conversion of the CO bond of ketones to a CN bond using ammonium salts as the nitrogen source

The copper-catalyzed conversion of the CO bond of ketones to a CN bond is described using ammonium salts as the nitrogen source in the presence of molecular oxygen.