Potassium hydroxide/dimethyl sulfoxide promoted intramolecular cyclization for the synthesis of benzimidazol-2-ones

Polymorphic structures of 3-phenyl-1H-1,3-benzo-diazol-2(3H)-one

The polymorphic structures (I and II) of 3-phenyl-1H-1,3-benzo-diazol-2(3H)-one, C₁₃H₁₀N₂O, acquired from pentane diffusion into the solution in THF, are reported. The structures show negligible differences in bond distances and angles, but the C-N-C-C torsion angles between the backbone and the phenyl substituent, 123.02 (15)° for I and 137.18 (11)° for II, are different. Compound I features a stronger C=O⋯H-N hydrogen bond than that in II, while the structure of II exhibits a stronger π-π inter-action than in I, as confirmed by the shorter inter-centroid distance [3.3257 (8) Å in II in comparison to 3.6862 (7) Å in I]. Overall, the supra-molecular inter-actions of I and II are distinct, presumably originating from the variation in the dihedral angle.

Construction of Benzimidazolone Derivatives via Aryl Iodide Catalyzed Intramolecular Oxidative C-H Amination

The first aryl iodide catalyzed intramolecular C-H amination of phenylurea has been disclosed for high-efficiency synthesis of benzimidazolone derivatives in excellent yields (up to 97%) by an operationally simple one-step organocatalytic oxidative process. Fluorinated protic alcohols can efficiently accelerate the conversion of this transformation. The straightforward method has good functional group tolerance and can be performed with an inexpensive and readily accessible catalyst with high proficiency.

Generation of aryl radicals by redox processes. Recent progress in the arylation methodology

Arylation methods based on the generation and use of aryl radicals have been a rapidly growing field of research in recent years and currently represent a powerful strategy for carbon – carbon and carbon – heteroatom bond formation. The progress in this field is related to advances in the methods for generation of aryl radicals. The currently used aryl radical precursors include aryl halides, aryldiazonium and diaryliodonium salts, arylcarboxylic acids and their derivatives, arylboronic acids, arylhydrazines, organosulfur(II, VI) compounds and some other compounds. Aryl radicals are generated under mild conditions by single electron reduction or oxidation of precursors induced by conventional reagents, visible light or electric current. A crucial role in the development of the radical arylation methodology belongs to photoredox processes either catalyzed by transition metal complexes or organic dyes or proceeding without catalysts. Unlike the conventional transition metal-catalyzed arylation methods, radical arylation reactions proceed very often at room temperature and have high functional group tolerance. Without claiming to be exhaustive, this review covers the most important advances of the current decade in the generation and synthetic applications of (het)aryl radicals. Examples of reactions are given and mechanistic insights are highlighted.

The bibliography includes 341 references.

Organophosphorus chemistry based on elemental phosphorus: advances and horizons

The results of studies on the application of elemental phosphorus for the synthesis of important organophosphorus compounds are surveyed and summarized. Currently, this trend represents a synthetically, environmentally and technologically attractive alternative to classical organophosphorus chemistry based on toxic and corrosive phosphorus chlorides. Direct phosphination and phosphinylation of organic compounds with elemental phosphorus (discussed in the first part of the review) basically extend the range of available phosphines, phosphine chalcogenides and phosphinic acids and provides further development of their synthetic potential (discussed in the second part of the review). It is shown that the breakthrough in this area is largely due to the discovery of reactions of elemental phosphorus (white and red) with various electrophiles in superbasic suspensions and emulsions derived from alkali metal hydroxides and to the development of electrochemical, electrocatalytic and catalytic activation of white phosphorus.

The bibliography includes 299 references.

Crystal structure and Hirshfeld surface analysis of a new di-thio-glycoluril: 1,4-bis-(4-meth-oxy-phen-yl)-3a-methyl-tetra-hydro-imidazo[4,5-d]imidazole-2,5(1H,3H)-di-thione

In the title di­thio­glycoluril derivative, there is a difference in the torsion angles between the thio­imidazole moiety and the meth­oxy­phenyl groups on either side of the mol­ecule [C—N—C_ar—C_ar = 116.9 (2) and −86.1 (3)°]. The N—C—N bond angle on one side of the di­thio­glycoluril moiety is slightly smaller than the one on the opposite side [110.9 (2)° cf. 112.0 (2)°], probably as a result of the steric effect of the methyl group.

In the title di­thio­glycoluril derivative, C₁₉H₂₀N₄O₃S₂, there is a difference in the torsion angles between the thio­imidazole moiety and the meth­oxy­phenyl groups on either side of the mol­ecule [C—N—C_ar—C_ar = 116.9 (2) and −86.1 (3)°, respectively]. The N—C—N bond angle on one side of the di­thio­glycoluril moiety is slightly smaller compared to that on the opposite side, [110.9 (2)° cf. 112.0 (2)°], probably as a result of the steric effect of the methyl group. In the crystal, N—H⋯S hydrogen bonds link adjacent mol­ecules to form chains propagating along the c-axis direction. The chains are linked by C—H⋯S hydrogen bonds, forming layers parallel to the bc plane. The layers are then linked by C—H⋯π inter­actions, leading to the formation of a three-dimensional supra­molecular network. Hirshfeld surface analysis and two-dimensional fingerprint plots were used to investigate the mol­ecular inter­actions in the crystal.

Quinazolinone Synthesis through Base-Promoted SNAr Reaction of ortho-Fluorobenzamides with Amides Followed by Cyclization

A transition-metal-free synthesis of quinazolin-4-ones by Cs₂CO₃-promoted S_NAr reaction of ortho-fluorobenzamides with amides followed by cyclization in dimethyl sulfoxide has been developed. The present procedure can provide efficient synthetic methods for the formation of both 2-substituted and 2,3-disubstituted quinazolin-4-one rings depending on the use of easily available starting materials and an efficient, one-pot protocol for the synthesis of the marketed drug product of methaqualone.

Synthesis of Multisubstituted Benzimidazolones via Copper-Catalyzed Oxidative Tandem C-H Aminations and Alkyl Deconstructive Carbofunctionalization

Benzimidazolone constitutes the core structure of numerous pharmaceuticals, agrochemicals, inhibitors, pigments, herbicides, and fine chemicals. Amination of hydrocarbons is an attractive tool for the creation of nitrogen-containing products. However, the multiple steps, harsh conditions, and low atom efficiencies often present in these reactions remain challenging. We present a multicomponent synthesis of functional benzimidazolones from arylamines, dialkylamines, and alcohols, acting via the sequence of copper-catalyzed oxidative tandem C-H aminations and alkyl deconstructive carbofunctionalization. The catalytic transformation forms multiple bonds in one single operation, uses readily available feedstocks and a naturally abundant Cu/O2 catalyst system, has broad substrate scope, avoids pre-installation of aminating agents and directing groups, and provides high chemo- and regioselectivity, resulting in direct functionalization of inert C-H and C-C bonds via single-electron oxidation-induced activation mode. This platform can be expected to provide structurally diverse products with interesting biological, chemical, and physical properties.

Proton transfer in the benzimidazolone and benzimidazolthione tautomerism process catalyzed by polar protic solvents

The tautomeric equilibrium of benzimidazolone and benzimidazolthione have been studied by the density functional theory method using the CAM-B3LYP functional together with the 6-311G(d,p) basis set. Two separate mechanisms have been investigated: a direct intramolecular transfer using the polarizable continuum model and an indirect proton transfer assisted by a molecule of solvent (C6H12, H2O, CH3OH, and H2O2). In both cases, the results obtained indicate that ketone and thione are the most stable forms. However, the enhanced height of the activation barrier for the four-center mechanisms describing the tautomerism reaction as a direct intramolecular transfer implicates a relatively disadvantaged process. The participation of a polar protic solvent molecule allows the lowering of the activation energy barrier. Potential energy profiles of keto-enol and thio-enol tautomerism assisted by methanol and water are very different. The former one describes a concerted mechanism but the latter does not because it is associated with asynchronous processes that take place during the thio-enol tautomerism.

Base-Promoted SNAr Reactions of Fluoro- and Chloroarenes as a Route to N-Aryl Indoles and Carbazoles

KOH/DMSO-promoted C-N bond formation via nucleophilic aromatic substitution (S_NAr) between chloroarenes or fluoroarenes with indoles and carbazole under transition metal-free conditions affording the corresponding N-arylated indoles and carbazoles has been developed.

Synthesis of Indoles via Electron-Catalyzed Intramolecular C-N Bond Formation

A new protocol for the preparation of N-substituted indole-3-carboxylates has been developed. The key C-N bond formation occurs under transition-metal-free conditions employing a t-BuOK/DMF system without special initiators or additives. Across a number of substrates, indoles were afforded in yields higher or comparable to those obtained under transition-metal-catalyzed conditions. While demonstrating high functional group tolerance, new conditions are particularly attractive for manufacturing halogenated indoles that cannot be made in a pure form using other metal-based catalytic methods.

I2-Mediated transition-metal-free aromatic C–H amination for the synthesis of benzimidazol-2-ones and related heterocycles

A practical I₂-mediated aromatic C–H amination reaction was established for benzimidazol-2-one synthesis under transition-metal-free conditions. The present reaction can be performed directly from disubstituted amines and isocyanates without the purification of the urea intermediates in a scalable fashion.

Route to Benzimidazol-2-ones via Decarbonylative Ring Contraction of Quinoxalinediones: Application to the Synthesis of Flibanserin, A Drug for Treating Hypoactive Sexual Desire Disorder in Women and Marine Natural Product Hunanamycin Analogue

A simple and practical method to access a variety of benzimidazol-2-ones is reported here. A series of N-alkyl-substituted benzimidazol-2-ones were synthesized by decarbonylative ring contraction starting from corresponding quinoxalinediones for the first time. The utility of the method has been demonstrated by synthesizing recently approved controversial drug flibanserin (Addyi) and a urea analogue of marine antibiotic natural product hunanamycin-A.

Base-Mediated One-Pot Synthesis of Aliphatic Diazirines for Photoaffinity Labeling

Aliphatic diazirines have been widely used as prominent photophores for photoaffinity labeling owing to their relatively small size which can reduce the steric effect on the natural interaction between ligands and proteins. Based on our continuous efforts to develop efficient methods for the synthesis of aliphatic diazirines, we present here a comprehensive study about base-mediated one-pot synthesis of aliphatic diazirines. It was found that potassium hydroxide (KOH) can also promote the construction of aliphatic diazirine with good efficiency. Importantly, KOH is cheaper, highly available, and easily handled and stored compared with the previously used base, potassium tert-butoxide (t-BuOK). Gram-scale study showed that it owned great advantages in being used for the large-scale production of aliphatic diazirines. This protocol is highly neat and the desired products can be easily isolated and purified. As the first comprehensive study of the base-mediated one-pot synthesis of aliphatic diazirines, this work provided good insight into the preparation and utilization of diazirine-based photoaffinity labeling probes.

Synthesis of 1,4-dihydroquinoline derivatives under transition-metal-free conditions and their diverse applications

A transition-metal-free process for the synthesis of 1,4-dihydroquinoline derivatives starting from simple enaminones with aldehydes via intermolecular cascade cyclization in a one-pot protocol is developed. This methodology affords a variety of products in moderate to good yields. Particularly, the use of the enaminone fragment in 1,4-dihydroquinoline derivatives 3 as a leaving group for further diverse applications with C-nucleophiles is proved to be feasible.

Regioselective synthesis of benzimidazolones via cascade C-N coupling of monosubstituted ureas

A direct method for the regioselective construction of benzimidazolones is reported wherein a single palladium catalyst is employed to couple monosubstituted urea substrates with differentially substituted 1,2-dihaloaromatic systems. In this method, the catalyst is able to promote a cascade of two discrete chemoselective C–N bond-forming processes that allows the highly selective and predictable formation of complex heterocycles from simple, readily available starting materials.

Hypervalent iodine(iii) catalyzed oxidative C–N bond formation in water: synthesis of benzimidazole-fused heterocycles

A diverse array of benzimidazole-fused heterocycles was synthesized by in situ generated hypervalent iodine(iii) catalyzed intramolecular oxidative C–N bond formation in water and under ambient conditions.

Transition-metal-free synthesis of benzimidazoles mediated by KOH/DMSO

Benzimidazoles are prepared by intramolecular N-arylations of amidines mediated by potassium hydroxide in DMSO at 120 °C. In this manner, diversely substituted products have been obtained in moderate to very good yields.