CuI-Catalyzed C–N Bond Formation and Cleavage for the Synthesis of Benzimidazo[1,2-a]quinazoline Derivatives

Recent Advances in Metal-Catalyzed Approaches for the Synthesis of Quinazoline Derivatives

Quinazolines are an important class of heterocyclic compounds that have proven their significance, especially in the field of organic synthesis and medicinal chemistry because of their wide range of biological and pharmacological properties. Thus, numerous synthetic methods have been developed for the synthesis of quinazolines and their derivatives. This review article briefly outlines the new synthetic methods for compounds containing the quinazoline scaffold employing transition metal-catalyzed reactions.

Recent Advances in the Tandem Copper-Catalyzed Ullmann-Goldberg N-Arylation–Cyclization Strategies

N‒Aryl bond formation under copper catalysis has been playing a pivotal role and has been extensively used as a key step in the total syntheses of several therapeutic molecules. The...

Synthesis of Potent Anticancer Substituted 5-Benzimidazol-2-amino Thiazoles Controlled by Bifunctional Hydrogen Bonding under Microwave Irradiations

Benzimidazol-amino thiazoles are synthesized under microwave irradiations using benzimidazole phenyl thiourea and 2-bromoacetophenone. Bifunctional hydrogen bonding plays an important role in chemical conversion. The reaction was carried out by C-C bond formation, followed by C-N bond cleavage and simultaneous migration of the benzimidazole ring. This reaction is novel and efficient for the synthesis of benzimidazol-amino thiazoles in which microwaves were used as driving forces. Synthesis of the product was controlled by double hydrogen bonding which is practically confirmed by the synthesis of routine imino-thiazole as an alternative product in the simple acidic condition. The simple acidic condition is neither responsible nor sufficient for optimum conversion of the benzimidazole migrated product. The synthesized products benzimidazole amino thiazoles D4 (IC₅₀ = 4.207 μM) and D8 (IC₅₀ = 2.398 μM) show interesting anticancer activities for human lung cancer with reference to doxorubicin (IC₅₀ = 1.750 μM).

tert-Amino Effect-Promoted Rearrangement of Aryl Isothiocyanate: A Versatile Approach to Benzimidazothiazepines and Benzimidazothioethers

A general and practical approach to benzimidazothiazepine and benzimidazothioether derivatives via an intramolecular nucleophilic addition/ring expansion rearrangement of aryl isothiocyanates promoted by the tert-amino effect has been developed. This reaction is catalyzed by low-cost camphorsulfonic acid and tolerates a broad substrate scope with complete atom economy. Structurally intriguing benzimidazothiazepine and benzimidazothioether products could be easily obtained by a simple operation in good to excellent yield (up to 98%).

Switchable Copper-Catalyzed Approach to Benzodithiole, Benzothiaselenole, and Dibenzodithiocine Skeletons

A copper-catalyzed reaction between 2-bromo-benzothioamides and S8 or Se involving sulfur rearrangement is reported, enabling access to benzodithioles 2 and benzothiaselenoles 6 in the presence of Cs2CO3. In the absence of S8 or Se, the reaction affords dibenzodithiocines 7 via two consecutive C(sp2)-S Ullmann couplings.

An efficient synthesis of 16H-dibenzo[2,3:6,7][1,4]oxazepino[5,4-b]quinazolin-16-ones via an Ullmann reaction catalyzed by CuI

CuI functions as a mild Lewis acid catalyst to promote the condensation and cyclization reaction of 2-amino-N-(2-hydroxyphenyl)benzamide and 2-bromobenzaldehyde to build the quinazoline moiety first. With the addition of Cs₂CO₃, it also can catalyse the subsequent intramolecular Ullmann type reaction to give 16H-dibenzo[2,3:6,7][1,4]oxazepino[5,4-b]quinazolin-16-ones in good yields.

Synthesis of Pyrimidine- and Quinazoline-Fused Benzimidazole-4,7-diones Using Combinatorial Cyclocondensation and Oxidation

β-Bromo-α,β-unsaturated aldehydes and 2-bromobenzaldehydes react with 4,7-dimethoxy-1H-benzo[d]imidazole-2-amine by microwave irradiation in dimethylformamide in the presence of a base to give the corresponding dimethoxy-substituted benzo[4,5]imidazo[1,2-a]pyrimidines and benzo[4,5]imidazo[1,2-a]quinazolines, respectively, in moderate to good yields. Oxidation of such N-fused hybrid scaffolds by aqueous ceric ammonium nitrate affords pyrimidine- and quinazoline-fused benzimidazole-4,7-diones in high yields.

Synthesis of Substituted 4 H-Thiochromen-4-imines via Copper-Catalyzed Cyclization Cascades of o-Bromobenzothioamides with Terminal Alkynes

A series of ( E)- N-aryl-4 H-thiochromen-4-imines has been conveniently obtained through a cascade reaction between o-bromobenzothioamides and terminal alkynes. This novel approach probably involved an initial generation of benzothietane-2-imine intermidates via an intramolecular Ullmann reaction under CuI/L-proline cocatalysis and alkaline conditions followed by imine alkynylation, ring opening, and cyclization sequences to provide the unexpected 4 H-thiochromen-4-imines rather than isothiochromans.

Synthesis of Symmetric and Unsymmetric Secondary Amines from the Ligand-Promoted Ruthenium-Catalyzed Deaminative Coupling Reaction of Primary Amines

The catalytic system generated in situ from the tetranuclear Ru-H complex with a catechol ligand (1/L1) was found to be effective for the direct deaminative coupling of two primary amines to form secondary amines. The catalyst 1/L1 was highly chemoselective for promoting the coupling of two different primary amines to afford unsymmetric secondary amines. The analogous coupling of aniline with primary amines formed aryl-substituted secondary amines. The treatment of aniline- d₇ with 4-methoxybenzylamine led to the coupling product with significant deuterium incorporation on CH₂ (18% D). The most pronounced carbon isotope effect was observed on the α-carbon of the product isolated from the coupling reaction of 4-methoxybenzylamine (C(1) = 1.015(2)). A Hammett plot was constructed from measuring the rates of the coupling reaction of 4-methoxyaniline with a series of para-substituted benzylamines 4-X-C₆H₄CH₂NH₂ (X = OMe, Me, H, F, CF₃) (ρ = -0.79 ± 0.1). A plausible mechanistic scheme has been proposed for the coupling reaction on the basis of these results. The catalytic coupling method provides an operationally simple and chemoselective synthesis of secondary amine products without using any reactive reagents or forming wasteful byproducts.

One-step construction of complex polyheterocycles via a sequential post-GBB cyclization/spiro ring expansion triggered by a [1,5]-hydride shift

An efficient tandem route to novel amino-indazolo[3′,2′:2,3]imidazo[1,5-c]quinazolin-6(5H)-ones has been explored.

An efficient synthesis of 6-arylbenzo[4,5]imidazo[2,1-a]isoquinolines via sequential α-arylation of carbonyl and deacylation catalyzed by CuI

Dibenzoyl methane was found to undergo α-arylation of carbonyl and deacylation reaction with 2-(2-bromophenyl)-1H-benzo[d]imidazoles catalyzed by CuI in the presence of Cs₂CO₃, and provided an efficient synthesis of 6-arylbenzo[4,5]imidazo[2,1-a]isoquinolines.

Chemoselective acylation of benzimidazoles with phenylacetic acids under different Cu catalysts to give fused five-membered N-heterocycles or tertiary amides

C-N bond formation via a copper-catalyzed aerobic oxidative decarboxylative tandem protocol was realized. The phenylacetic acids which contain ortho-X (X = F or Br) on the aromatic ring will render a fused five-membered heterocycle via a tandem aromatic nucleophilic substitution and aerobic oxidative decarboxylative acylation at the C(sp(2))-H bond of benzimidazoles under the Cu(OAc)2/K2CO3/BF3·Et2O catalytic system, while with CuBr as the catalyst and pyridine as the base, N-acylation occurred and tertiary amides were obtained.

Copper-catalyzed tandem Ullmann type C-N coupling and dehydrative cyclization: synthesis of imidazo[1,2-c]quinazolines

A simple and efficient one-pot protocol has been demonstrated for the synthesis of imidazo[1,2-c]quinazoline derivatives through a copper catalyzed tandem reaction between substituted 2-(2-bromophenyl)-1H-imidazoles and formamide. The synthetic protocol involves initial Ullmann-type C-N coupling followed by intramolecular dehydrative cyclization. The method uses readily available 2-(2-bromophenyl)-1H-imidazoles as the starting materials to afford imidazo[1,2-c]quinazolines in moderate to good yields and provided 610 mg (71%) yield of 3a from a gram scale reaction.

Copper(ii) supported on magnetic chitosan: a green nanocatalyst for the synthesis of 2,4,6-triaryl pyridines by C–N bond cleavage of benzylamines

In this paper, Cu/magnetic chitosan has been synthesized and used as a new green nanocatalyst for highly efficient synthesis of 2,4,6-triaryl pyridines via C–N bond cleavage of benzylamines under aerobic oxidation at 90 °C.