Transition metal-free one-pot synthesis of nitrogen-containing heterocycles

Progress in Continuous Flow Synthesis of Hydrogen-Bonded Organic Framework Material Synthons

Hydrogen-bonded organic framework (HOF) materials are typically formed by the self-assembly of small organic units (synthons) with specific functional groups through hydrogen bonding or other interactions. HOF is commonly used as an electrolyte for batteries. Well-designed HOF materials can enhance the proton exchange rate, thereby boosting battery performance. This paper reviews recent advancements in the continuous synthesis of HOF synthons, in the continuous synthesis of HOF's unit small molecules enabling the multi-step, rapid, and in situ synthesis of synthons, such as carboxylic acid, diaminotriazine (DAT), urea, guanidine, imidazole, pyrazole, pyridine, thiazole, triazole, and tetrazole, with online monitoring. Continuous flow reactors facilitate fast chemical reactions and precise microfluidic control, offering superior reaction speed, product yield, and selectivity compared to batch processes. Integrating the continuous synthesis of synthons with the construction of HOF materials on a single platform is essential for achieving low-cost, safe, and efficient processing, especially for reactions involving toxic, flammable, or explosive substances.

Metal-free oxoammonium salt-mediated C(sp3)-H oxidative Ugi-azide multicomponent reaction

In this work, an efficient oxidative C(sp³)-H Ugi-azide multicomponent reaction of cyclic benzylic amines to the corresponding α-tetrazolo compounds using a TEMPO salt as mild hydride abstractor-type oxidant is reported. This simple one-pot approach allows the direct functionalization of N-heterocycles such as tetrahydroisoquinolines with a variety of isocyanides and NaN₃ as a practical azide source. The reaction proceeds at room temperature and without the need of acid additives, allowing for the use of sensitive substrates, while minimizing isocyanide polymerization to provide the desired heterocycle-tetrazole products in synthetically useful yields (up to 99%).

One-Pot Construction of Diverse β-Lactam Scaffolds via the Green Oxidation of Amines and Its Application to the Diastereoselective Synthesis of β-Amino Acids

In this study, a simple one-pot construction of β-lactam scaffolds was successfully achieved via 4,6-dihydroxysalicylic acid-catalyzed organocatalytic oxidation of amines to imines using molecular oxygen. Although some imines are highly unstable and difficult to isolate by conventional methods, the organocatalytic oxidation of amines described herein, followed by their direct reaction with acyl chlorides in the presence of a base, afforded a series of new β-lactam derivatives with excellent cis selectivity, which could not be synthesized and isolated by previously reported methods. Thus, this one-pot protocol will be one of the powerful methods applicable to the synthesis of various potential drug candidates and functional molecules. Furthermore, the subsequent hydrolysis of these β-lactams successfully afforded the corresponding β-amino acids as almost single diastereomers in up to 99% yields.

Recent developments in the synthesis of azaindoles from pyridine and pyrrole building blocks

The azaindole framework is ubiquitous in bioactive natural products and pharmaceuticals. This review highlights the synthetic approaches to azaindoles with advantages and limitations, mechanistic pathways and biological importance.

Denitrative imino-diaza-Nazarov cyclization: synthesis of pyrazoles

An iodine-catalyzed denitrative imino-diaza-Nazarov cyclization (DIDAN) methodology has been developed for the synthesis of pyrazoles with high to excellent yields by using α-nitroacetophenone derivatives and in situ generated hydrazones. The key transformation of this oxidative 4π-electrocyclization proceeds through an enamine-iminium ion intermediate. This rapid one-pot DIDAN protocol results in the selective generation of C-C and C-N bonds and cleavage of a C-N bond.

Synthesis and Antimicrobial Evaluation of Some Novel Pyrimidine, Pyrazole, Chromene and Tetrahydrobenzo[b]thiophene Derivatives Bearing Pyrimidinthione Moiety

AIM AND OBJECTIVE

A novel collection of fused pyrimidine, pyridine, pyrazole, chromene and thiophene derivatives 2-30 have been newly synthesized by using the 1a, b as starting material. Fused pyrane exhibits a range of pharmacological activity such as cancer agents [1], antimicrobial [2-4], antioxidant [5], antiproliferative [6], cytotoxic activity [7], anticipated antitumor [8], antiparkinsonian [9] and anti-inflammatory [10]. Moreover, pyrane derivatives are well known for bacterial biofilm disruptor [11], anticonvulsant [12] and inhibitors of mycobacterium bovis [13].

MATERIALS AND METHODS

All melting points were measured using the Akofler Block instrument and are uncorrected. IR spectra (KBr) were recorded on a FTIR 5300 spectrometer (υ, cm-1). The 1H-NMR spectra were recorded on a Varian Gemini spectrometer. The 1H-NMR spectra were run at 300, 400 MHz and 13C-NMR spectra were run at 100 MHz in DMSO-d6, CDCl3 as solvents. The chemical shifts are expressed in parts per million (ppm) by using tetramethylsilane (TMS) as an internal reference, 1000 EX mass spectrometer at 70 eV. The purity of synthesized compounds was checked by thin-layer chromatography (TLC) (aluminum sheets) using nhexane, EtOAc (9:1, V/V, 7:3 V/V) eluent. Elemental analyses were carried out by the Microanalytical Research Center, Faculty of Science, and Microanalytical Unit, Faculty of Pharmacy, Cairo University, Egypt.

RESULTS AND DISCUSSION

A novel series of azoles and azines were designed and prepared via the reaction of 7-amino- 5-(4-chlorophenyl)-4-phenyl-2-thioxo-2,5-dihydro-1H-pyrano- [2,3-d]pyrimidine-6-carbonitrile 1a and 7-amino-4,5- diphenyl-2-thioxo-2,5-dihydro-1H-pyrano[2,3-d]-pyrimidine-6-carbonitrile 1b with some electrophilic and nucleophilic reagents. The structures of target compounds were confirmed by elemental analyses and spectral data. The novel synthesized compounds showed good antimicrobial activity against the previously mentioned microorganisms.

CONCLUSION

In conclusion, compounds 1a, 1b underwent ready cyclization to give fused heterocyclic compounds through reaction with different reagents and under different conditions and subjected to antimicrobial screening.

Cinnoline Scaffold-A Molecular Heart of Medicinal Chemistry?

The cinnoline nucleus is a very important bicyclic heterocycle that is used as the structural subunit of many compounds with interesting pharmaceutical properties. Cinnoline derivatives exhibit broad spectrum of pharmacological activities such as antibacterial, antifungal, antimalarial, anti-inflammatory, analgesic, anxiolytic and antitumor activities. Some of them are under evaluation in clinical trials. In the present review, we have compiled studies focused on the biological properties of cinnoline derivatives conducted by many research groups worldwide between 2005 and 2019. Comprehensive and target oriented information clearly indicate that the development of cinnoline based molecules constitute a significant contribution to the identification of lead compounds with optimized pharmacodynamic and pharmacokinetic properties.

First Metal-Free Synthesis of Tetracyclic Pyrido and Pyrazino Thienopyrimidinone Molecules

We report herein a new metal free synthetic pathway to generate tetracyclic compounds from 3-aminothieno[3,2-b]pyridine-2-carboxylate. To enlarge the molecular diversity, we studied the Suzuki coupling of 9-chloro-6H-pyrido[1,2-a]pyrido[2′,3′:4,5]thieno[3,2-d]pyrimidin-6-one and several boronic acids were easily introduced.

Chemo-, Regio-, and Stereoselective N-Alkenylation of Pyrazoles/Benzpyrazoles Using Activated and Unactivated Alkynes

Transition-metal-free chemo-, regio-, and stereoselective synthesis of (Z) and (E) styryl pyrazoles and benzpyrazoles by the addition of N-heterocycles onto functionalized terminal and internal alkynes using a super basic solution of KOH/DMSO has been described. The stereochemical outcome of the reaction was governed by time and quantity of the base. The reaction of pyrazoles and benzpyrazoles onto alkynes takes place chemoselectively without affecting the free -NH₂ group of pyrazoles and -OH group of alkynes. The designed protocol was well implemented on alkynes bearing long alkyl chain, an alicyclic ring, hydroxy, ether, and ester functionality, which offer the N-alkenylated products in good yields. This developed methodology also provides easy access for the synthesis of bis-vinylated heterocycles. The presence of free -NH₂, -OH, -COOR, and halo group in styryl pyrazoles, could be further utilized for synthetic elaboration, which is advantageous for biological evaluation. For the first time, we have disclosed the base-mediated conversion of (Z)-styryl pyrazoles to (E)-styryl pyrazoles in KOH/DMSO system. The cis-trans isomerization was supported by the control experiments and deuterium labeling studies.