Ruthenium-Catalyzed Divergent Acceptorless Dehydrogenative Coupling of 1,3-Diols with Arylhydrazines: Synthesis of Pyrazoles and 2-Pyrazolines

Reagent-assisted regio-divergent cyclization synthesis of pyrazole

The present study reveals a practical one-pot base-promoted regio-divergent cyclization of hydrazines with alkynyl silane under mild conditions, facilitating the synthesis of diverse silicone-substituted pyrazoles and functionalized pyrazoles in great yields with exceptional selectivity. This protocol is expected to afford a streamlined one-pot approach for the synthesis of multiple compounds in water.

Ligand Assisted Co(II)-Catalyzed Multicomponent Synthesis of Substituted Pyrroles and Pyridines

Herein, we describe a sustainable Co(II)-catalyzed synthesis of pyrroles and pyridines. Using a Co(II)-catalyst [CoII 2(La)2Cl2] (1 a) bearing redox-active 2-(phenyldiazenyl)-1,10-phenanthroline) (La) scaffold, various substituted pyrroles and pyridines were synthesized in good yields, taking alcohol as one of the primary feedstock. Pyrroles were synthesized by the equimolar reaction of 2-amino and secondary alcohols. A series of 2,4,6-substituted symmetrical pyridines were prepared via a three-component reaction of NH4OAc with 1 : 2.2 molar primary and secondary alcohols, respectively. Unsymmetrically substituted 2,4,6-trisubstituted, 2,4,5,6-tetrasubstituted, and 2,3,4,5,6-pentasubstituted pyridines were achieved via a multi-component coupling reaction of alcohols and NH4OAc. Catalyst 1 a showed encouraging results during the gram-scale synthesis of these N-heterocycles. Mechanistic investigation revealed synergistic involvement of cobalt metal and the ligand during the catalytic reactions.

Regioselective Synthesis of N-Aryl Pyrazoles from Alkenyl Sulfoxonium Ylides and Aryl Diazonium Salts

A convenient and practical method has been developed for synthesizing various N-aryl pyrazoles from vinyl sulfoxonium ylides and diazonium salts. When using 1,3-disubstituted vinyl sulfoxonium ylides, the reaction selectively yields 1,3,5-trisubstituted pyrazoles. On the other hand, employing 2,3-disubstituted vinyl sulfoxonium ylides results in the formation of 1,3,4-trisubstituted pyrazoles. The reaction proceeds through the novel aryl diazene-derived vinyl sulfoxonium ylide. Furthermore, this method efficiently produces pyrazoles from aniline derivatives in a one-pot transformation. The reaction takes place under transition metal-free, mild conditions using easily accessible starting materials, making it a practical approach for generating pyrazoles in pharmaceutical chemistry.

Ruthenium-Catalyzed Synthesis of 2-Pyrazolines via Acceptorless Dehydrogenative Coupling of Allylic Alcohols with Hydrazines

Described herein is the synthesis of 2-pyrazolines via acceptorless dehydrogenative coupling of allylic alcohols with hydrazines based on a Ru3(CO)12/NHC-phosphine-phosphine ligand L catalytic system. The reaction not only exhibits low catalyst loading (only 0.3 mol %), wide substrate scope, good to excellent yields, and high selectivity but also omits the use of sacrificial hydrogen acceptor with only H2 and H2O as byproducts, making the reaction green and atom-economical.

A multi-component synthetic route for 2-pyrazolines via acceptorless dehydrogenation of alcohols using homogeneous Ni(II) catalysts

Herein, we present the first efficient and sustainable multicomponent synthesis (MCS) of 2-pyrazolines using acceptorless dehydrogenation of benzyl alcohols catalysed by nickel(II) catalysts. Two air-stable phosphine free nickel(II) complexes anchored by NNN-type pincer ligands were synthesized and efficiently used in the MCS of 40 distinct pyrazoline derivatives.

Serendipitous Conversion of an Acetylamino Dideoxy-Octonic Acid Derivate into a Functionalized Carbohydrate-Pyrazole Conjugate and Investigation of the Method´s General Applicability

By treatment of the peracetylated methylester of 4-acetylamino-2,4-dideoxy-d-glycero-d-galacto-octonic acid (ADOA-PAE) with nitrosyl tetrafluoroborate, a serendipitous formation of a highly functionalized carbohydrate-pyrazole conjugate was observed in 95% yield. This observation is remarkable, as it involves a five-step one-pot synthesis that proceeds via an 1,3-acyl shift and a 1,5-electrocyclization, which usually requires thermal conditions; however, the reaction occurred at a temperature of 0 °C. Additionally, the excellent yield of the carbohydrate-decorated pyrazole and the regiospecificity of the cyclization are of particular interest, as regioselectivity is always a challenge in pyrazole synthesis. Subsequently, this novel access to pyrazoles starting from N-acetyl-allyl amides via nitrosation and electrocyclization was investigated. In addition, mechanistic studies for the formation of substituted pyrazoles of type were carried out.

Highly selective and additive-free Pd(OAc)2/CPP catalyzed hydroaminocarbonylation of alkynes

Herein, the synthesis of branched α,β-unsaturated amides by a hydroaminocarbonylation reaction of alkynes with various amine substrates such as aromatic amines, aliphatic amines, solid amine sources like NH4HCO3, and even strongly basic piperidines is reported, using a Pd(OAc)2/hybrid N-heterocyclic carbene-phosphine-phosphine (CPP) catalytic system. The reactions feature no additives, wide substrate scope, high selectivity (b/l > 99 : 1) and excellent yields. Mechanistic studies have disclosed that the reaction takes place via a palladium hydride pathway. CPP adopts a hybrid bidentate ligand conformation with a carbene-phosphine coordination mode, wherein one phosphorus atom remains externally accessible, potentially serving as a stabilizing auxiliary during catalytic cycles.

Divergent Synthesis of Pyrazoles via Manganese Pincer Complex Catalyzed Acceptorless Dehydrogenative Coupling Reactions

This report detailed the synthesis of multi-substituted pyrazoles through the acceptorless dehydrogenative coupling (ADC) reaction catalyzed by a well-defined manganese(I)-pincer complex. Symmetrically substituted pyrazoles were synthesized by reacting 1,3-diols with hydrazines. Unsymmetrically substituted pyrazoles were selectively made via the ADC of primary alcohols with methyl hydrazones. Water and hydrogen are liberated as the green byproducts. The endurance of these methodologies has been presented by producing 30 substrates with varied functionalities. Model reactions were scaled up to demonstrate practicability. The reaction rate and order were measured to transparent the involvement of the reagents during catalysis. Control experiments elucidated the plausible reaction mechanisms.

Acetic Acid-Catalyzed (3 + 2) Cyclization of 2-Aroyl-3-aryl-1,1-dicyanocyclopropanes with Arylhydrazines: To trans-4-Dicyanomethyl-1,3,5-triaryl-4,5-dihydropyrazoles

Acetic acid-catalyzed (3 + 2) cyclization reaction of substituted 2-aroyl-3-aryl-1,1-dicyanocyclopropanes with arylhydrazines was investigated for the efficient synthesis of 4-dicyanomethyl-1,3,5-triaryl-4,5-dihydropyrazoles in good yields, in which 4,5-double substituents are predominantly trans selective. This approach included the consecutive condensation, ring opening, and double nucleophilic cyclization reaction.

Density functional modeling, and molecular docking with SARS-CoV-2 spike protein (Wuhan) and omicron S protein (variant) studies of new heterocyclic compounds including a pyrazoline nucleus

Nowadays, different vaccines and antiviral drugs have been developed and their effectiveness has been proven against SARS-CoV-2. Pyrazoline derivatives are biologically active molecules and exhibit broad-spectrum biological activity properties. In this scope, four new molecules (4a-d) including a pyrazoline core were synthesized in order to predict their antiviral properties theoretically. Compounds 4a-d were purified by the crystallization method. The structures of 4a-d were completely characterized by NMR, IR, and elemental analysis. The molecular structures of the compounds in the ground state have been optimized using density functional theory with the B3LYP/6-31++G(d,p) level. The quantum chemical parameters were predicted by density functional theory calculations. Moreover, the molecular docking studies of 4a-d with SARS-CoV-2 Spike protein (Wuhan) and omicron S protein (variant) were presented to investigate and predict potential interactions. The binding sites, binding types and energies, bond distances of the non-covalent interactions and calculated inhibition constants (calc. Ki) as a consequence of molecular docking for 4a-d were presented in this study. Furthermore, the stability of the protein-4a complex obtained from the docking was investigated through molecular dynamics simulation.Communicated by Ramaswamy H. Sarma.

Recent advances in C/N-alkylation with alcohols through hydride transfer strategies

This review highlights the most recent reports in three powerful and ever-growing fields of borrowing hydrogen, acceptorless dehydrogenative coupling, and base-mediated hydride transfer strategies; which pave the way for generating reactive intermediates via shuttling hydrogen (or hydride) between starting materials without any need for an external hydrogen source to easily construct more complex structures. There is a thorough focus on diversifying the utility of alcohols for C/N-alkylation leading to the synthesis of branched ketones, alcohols, amines, indols, and 6-membered nitrogen-containing heterocycles such as pyridines and pyrimidines, various transformations with the focus on C-C and C-N bond-forming reactions via metal-based catalysis or metal-free approaches in this context to give a global overview in this area.