An efficient four-component domino protocol for the rapid and green synthesis of functionalized benzo[a]pyrano[2,3-c]phenazine derivatives using caffeine as a homogeneous catalyst

A new DES-mediated synthesis of Henna-based benzopyranophenazines and benzoxanthenetriones

MTPPBr/THFTCA-DES was prepared as a new deep eutectic solvent (DES) from a mixture (molar ratio 7:3) of methyltriphenyl-phosphonium bromide (MTPPBr) and tetrahydrofuran-2,3,4,5-tetra-carboxylic acid (THFTCA), and characterized with various spectroscopic techniques, densitometer, and eutectic point. Then, it was used as a new and powerful catalyst for the synthesis of two sets of biologically important compounds, namely the Henna-based benzopyranophenazines and benzoxan-thenetriones. Solvent-free conditions, short reaction time, high efficiency, and easy recycling and separation of the DES catalyst are among the most important features of the presented method. Also, there is a nice consistency between the proposed structure of the DES compound, the integration values of the 1H NMR peaks, and the ratio of MTPPBr to THFTCA obtained from the eutectic point phase diagram. In addition, the reduction of peak splitting patterns in DES compared to the two primary materials can be good evidence of the formation of hydrogen bonds between the two components.

Greening up organic reactions with caffeine: applications, recent developments, and future directions

Numerous studies in the field of alkaloid chemistry have provided researchers with valuable insights into their unique properties as catalysts. Among the diverse natural catalysts, caffeine has emerged as a green, expedient, and biodegradable catalyst with high efficiency and applicability. Interest in using caffeine as a catalyst has burgeoned over the past few years with its role in diverse multicomponent reactions. Preparation of its imidazolium salts and further conversion to Nitrogen Heterocyclic Carbene (NHC) ligands and ionic liquids offers new paradigms. Caffeine has also played a multifaceted role as a support material in influencing the structural properties of nanoparticles. We hope that the chemistry of caffeine and its applications for sustainable organic transformations discussed in this review will stimulate new thinking and open new avenues in this field.

Introducing a green nanocatalytic process toward the synthesis of benzo[a]pyrano-[2,3-c]phenazines utilizing copper oxide quantum dot-modified core-shell magnetic mesoporous silica nanoparticles as high throughput and reusable nanocatalysts

In this contribution, a green, simple, efficient, and straightforward nanocatalytic process was developed for the synthesis of benzo[a]pyrano[2,3-c]phenazine derivatives under mild thermal conditions. In this regard, the copper oxide quantum dot-modified magnetic silica mesoporous nanoparticles (M-MSNs/CuO(QDs)) were synthesized by surface modification of M-MSNs with CuO QDs to prepare a highly powerful magnetic core-shell nanocatalyst. The prepared nanocatalyst was then characterized for its functionality, size, morphology, elemental composition, surface area, crystallinity, and magnetic properties. Afterwards, it was applied for the synthesis of benzo[a]pyrano[2,3-c]phenazine derivatives under green reaction conditions. The factors affecting the reaction yield were optimized by the one-factor-at-a-time optimization method. Under obtained optimal conditions, the developed method showed a reaction yield range as high as 86-95% for different derivatives. The reusability studies were performed for indexing the cycling stability of the prepared magnetic nanocatalyst. The results exhibited that the catalytic efficiency of the nanocatalyst was saved for at least 5 operational times, showing high cycling stability of M-MSNs/CuO(QDs). Finally, the catalytic performances of the nanocatalyst was compared with the reported ones, revealing that the M-MSNs/CuO(QDs) presents very better performances toward the synthesis of benzo[a]pyrano[2,3-c]phenazine derivatives than the reported ones.

A review on lawsone-based benzo[a]phenazin-5-ol: synthetic approaches and reactions

Phenazine systems are an important class of aza-polycyclic compounds that are easily found in nature and isolated as secondary metabolites primarily from Pseudomonas, Streptomyces, and a few other genera from soil or marine habitats. Moreover, various synthetic phenazine analogs are known for their pharmaceutical activities. Among various phenazines, benzo[a]phenazines are structural subunits in a variety of important natural products and have been given special attention due to their unique biological properties in various fields. In this review article, we highlight the synthesis of benzo[a]phenazin-5-ol derivatives from lawsone and benzene-1,2-diamines and their applications for the construction of a variety of five and six membered fused heterocycles such as pyranophenazines, spiropyranophenazines, pyridophenazines, furophenazines, benzochromenophenazines and oxazinophenazines during the period of 1995 to 2021.

Dicarbonyl compounds in the synthesis of heterocycles under green conditions

Carbon–carbon and carbon-heteroatom bond forming reactions are strategically employed for the generation of a variety of heterocyclic systems. This class of compounds represents the most general structural unit, present in many natural compounds. They are recognized for their valuable biologically properties and wide range of applications in medicinal, pharmaceutical, and other related fields of chemistry. This is an updated review on the use of dicarbonyl compounds under environmentally friendly conditions to access a series of heterocyclic structures, e.g., quinoxaline, quinazolinones, benzochalcogenazoles, indoles, among others. Synthetic protocols involving copper-catalyzed, multicomponent and cascade reactions, decarboxylative cyclization, recycling of CO2, and electrochemical approaches are presented and discussed.

Chitosan-attached nano-Fe3O4 as a superior and retrievable heterogeneous catalyst for the synthesis of benzopyranophenazines using chitosan-attached nano-Fe3O4

A simple and rapid method for the preparation of benzopyranophenazines is presented, involving a one-pot four-component reaction of hydroxynaphthoquinone, o-phenylenediamine, benzaldehydes, and malononitrile with nano-Fe3O4@chitosan as an efficient heterogeneous solid acid catalyst under reflux conditions in ethanol. The catalyst is characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), magnetic susceptibility measurements, energy-dispersive X-ray spectroscopy (EDS), and Fourier transform infrared (FT-IR) spectroscopy. Atom economy, high catalytic activity, a wide range of products, excellent yields in short reaction times, and low catalyst loading are some of the important features of this method.

Multisulfonate hyperbranched polyglycerol functionalized graphene oxide as an efficient reusable catalyst for green synthesis of benzo[a]pyrano-[2,3-c]phenazines under solvent-free conditions

A novel acid catalyst was prepared based on growing hyperbranched polyglycerol (HPG) on the surface of graphene oxide. Then, the hydroxyl groups of HPG on graphene oxide were functionalized by sulfonate groups to form an acid catalyst. The catalyst displayed a good loading level of acidic groups on the surface because of coating graphene oxide with HPG. This new catalyst is demonstrated to be highly effective in the preparation of benzo[a]pyrano[2,3-c]phenazine dyes.

An efficient and environmentally sustainable domino protocol for the synthesis of structurally diverse spiroannulated pyrimidophenazines using erbium doped TiO2 nanoparticles as a recyclable and reusable heterogeneous acid catalyst

An efficient and environmentally sustainable domino protocol has been presented for the synthesis of structurally diverse spiroannulated pyrimidophenazines involving a four component reaction of 2-hydroxynaphthalene-1,4-dione, benzene-1,2-diamine, cyclic ketones and amino derivatives in the presence of erbium doped TiO2 nanoparticles as a recyclable and reusable heterogeneous acid catalyst. The present synthetic protocol features mild reaction conditions with operational simplicity, excellent yield with high purity, short reaction time and high atom economy with the use of a recoverable and reusable environmentally sustainable heterogeneous catalyst.

Recent developments in the isolation, biological function, biosynthesis, and synthesis of phenazine natural products

Phenazines are natural products which are produced by bacteria or by archaeal Methanosarcina species. The tricyclic ring system enables redox processes, which producing organisms use for oxidation of NADH or for the generation of reactive oxygen species (ROS), giving them advantages over other microorganisms. In this review we summarize the progress in the field since 2005 regarding the isolation of new phenazine natural products, new insights in their biological function, and particularly the now almost completely understood biosynthesis. The review is complemented by a description of new synthetic methods and total syntheses of phenazines.

Microwave-Assisted and L-proline Catalysed Domino Cyclisation in an Aqueous Medium: A Rapid, Highly Efficient and Green Synthesis of Benzo[a]Phenazine Annulated Heterocycles

A highly efficient one-pot, two-step microwave-assisted procedure was applied for the rapid and green synthesis of benzo[a]phenazine annulated heterocyclic ring systems from the three- or four-component condensation reactions of 2-hydroxynaphthalene-1,4-dione, o-phenylenediamine, aromatic aldehydes and 1,3-indandione using L-proline as a bifunctional organocatalyst in water. This new procedure has a number of advantages such as high yields, very short reaction times, operational simplicity, simple work-up procedures and avoidance of hazardous or toxic catalysts and organic solvents. Moreover, the catalyst can be recovered and reused several times without much loss of its performance.

Theophylline as the catalyst for the diastereoselective synthesis of trans-1,2-dihydrobenzo[a]furo[2,3-c]phenazines in water

Theophylline-catalyzed efficient and environmentally benign procedure for the diastereoselective synthesis of trans-1,2-dihydrobenzo[a]furo[2,3-c]phenazines with pyridinium ylide assisted domino reaction in water.