Straightforward synthesis of pyrrolo[3,4-b]quinolines through intramolecular Povarov reactions

BF3·OEt2-catalyzed/mediated alkyne cyclization: a comprehensive review of heterocycle synthesis with mechanistic insights

The quest for efficient and versatile methods for heterocycle synthesis continues to drive innovation in organic chemistry. In this context, the cyclization of alkynes catalyzed or mediated by boron trifluoride diethyl etherate (BF3·OEt2) has emerged as a powerful and widely applicable strategy. This review provides a comprehensive and authoritative overview of BF3·OEt2-catalyzed/mediated alkyne cyclization reactions, covering the scope, mechanisms, and applications of these processes. We discuss the synthesis of a diverse range of heterocyclic compounds, including dihydropyrans, quinolines, dehydropiperidines, oxindoles and others, and highlight the unique advantages of BF3·OEt2 as a catalyst/mediator. Recent advances, challenges, and future directions in this rapidly evolving field are also addressed. This review aims to serve as a valuable resource for synthetic chemists, inspiring further research and applications in this exciting area.

The Intramolecular Povarov Tool in the Construction of Fused Nitrogen-Containing Heterocycles

Nitrogen heterocycles are part of the structure of natural products and agents with important biological activity, such as antiviral, antibiotic, and antitumor drugs. For this reason, heterocyclic compounds are one of today's most desirable synthetic targets and the Povarov reaction is a powerful synthetic tool for the construction of highly functionalized heterocyclic systems. This process involves an aromatic amine, a carbonyl compound, and an olefin or acetylene to give rise to the formation of a nitrogen-containing heterocycle. This review illustrates advances in the synthetic aspects of the intramolecular Povarov reaction for the construction of intricate nitrogen-containing polyheterocyclic compounds. This original review presents research done in this field, with references to important works by internationally relevant research groups on this current topic, covering the literature from 1992 to 2022. The intramolecular Povarov reactions are described here according to the key processes involved, using different combinations of aromatic or heteroaromatic amines, and aliphatic, aromatic, or heteroaromatic aldehydes. Some catalytic reactions promoted by transition metals are detailed, as well as the oxidative Povarov reaction and some asymmetric intramolecular Povarov processes.

Microwave-Assisted Domino Povarov-Type [4+2] Cycloaddition: A Rapid Access to 7-Phenyl-6H-chromeno[4,3-b]quinolines

A convenient, facile, and eco-friendly approach to synthesizing 7-phenyl-6H-chromeno[4,3-b]quinolines under microwave irradiation is presented. The current strategy enabled the synthesis of chromenoquinoline frameworks at 80 °C under shorter reaction times via intermolecular Schiff base formation followed by an intramolecular inverse demand hetero-Diels–Alder [4+2]-cycloaddition reaction by using a catalytic amount of copper triflate as the sole catalyst. Consequently, one C–N and two C–C bonds are constructed in a single pot, and a wide spread of 7-phenyl-6H-chromeno[4,3-b]quinolines have been synthesized with good functional group tolerance.

The Povarov Reaction: A Versatile Method to Synthesize Tetrahydroquinolines, Quinolines and Julolidines

The multicomponent Povarov reaction represents a powerful approach for the construction of substances containing N-heterocyclic frameworks. By using the Povarov reaction, in addition to accessing tetrahydroquinolines, quinolines and julolidines in a single step, it is possible to form the following new bonds: two Csp 3–Csp 3 and one Csp 3–Nsp 3, two Csp 2–Csp 2 and one Csp 2–Nsp 2, and four Csp 3–Csp 3 and two Csp 3–Nsp 1, respectively. This short review discusses the main features of the Povarov reaction, including its mechanism, the reaction scope by employing different catalysts and substrates, as well as stereoselective versions.

1 Introduction

2 Mechanism of the Povarov Reaction

3 Tetrahydroquinolines

4 Quinolines

5 Julolidines

6 Concluding Remarks

Recent advances in chemistry and therapeutic potential of functionalized quinoline motifs – a review

Quinoline, which consists of benzene fused with N-heterocyclic pyridine, has received considerable attention as a core template in drug design because of its broad spectrum of bioactivity. This review aims to present the recent advances in chemistry, medicinal potential and pharmacological applications of quinoline motifs to unveil their substantial efficacies for future drug development. Essential information in all the current and available literature used was accessed and retrieved using different search engines and databases, including Scopus, ISI Web of Knowledge, Google and PUBMED. Numerous derivatives of the bioactive quinolines have been harnessed via expeditious synthetic approaches, as highlighted herein. This review reveals that quinoline is an indisputable pharmacophore due to its tremendous benefits in medicinal chemistry research and other valuable areas of human endeavour. The recent in vivo and in vitro screening reported by scientists is highlighted herein, which may pave the way for novel drug development. Owing to the array of information available and highlighted herein on the medicinal potential of quinoline and its functionalized derivatives, a new window of opportunity may be opened to medicinal chemists to access more biomolecular quinolines for future drug development.

Quinoline, which consists of benzene fused with N-heterocyclic pyridine, has received considerable attention as a core template in drug design because of its broad spectrum of bioactivity.

Oxone promoted dehydrogenative Povarov cyclization of N-aryl glycine derivatives: an approach towards quinoline fused lactones and lactams

Oxone promoted intramolecular dehydrogenative imino Diels–Alder reaction (Povarov cyclization) of alkyne tethered N-aryl glycine esters and amides has been explored, thus affording biologically significant quinoline fused lactones and lactams.

Synthesis and Reactivity of Propargylamines in Organic Chemistry

Propargylamines are a versatile class of compounds which find broad application in many fields of chemistry. This review aims to describe the different strategies developed so far for the synthesis of propargylamines and their derivatives as well as to highlight their reactivity and use as building blocks in the synthesis of chemically relevant organic compounds. In the first part of the review, the different synthetic approaches to synthesize propargylamines, such as A³ couplings and C-H functionalization of alkynes, have been described and organized on the basis of the catalysts employed in the syntheses. Both racemic and enantioselective approaches have been reported. In the second part, an overview of the transformations of propargylamines into heterocyclic compounds such as pyrroles, pyridines, thiazoles, and oxazoles, as well as other relevant organic derivatives, is presented.

Design, synthesis and antiproliferative activity of decarbonyl luotonin analogues

A small library of benzimidazole-fused pyrrolo[3,4-b]quinoline has been synthesized from readily available benzimidazole 2-carbaldehyde and various substituted arylamines in good to excellent yields utilizing an intramolecular Povarov reaction catalyzed by boron trifluoride diethyl etharate as the key final step. The compounds thus synthesized can be considered as decarbonyl analogues of the anticancer alkaloid luotonin A and were evaluated in a DNA relaxation assay for their ability to inhibit human topoisomerase I. Interestingly, two of the compounds showed a remarkable activity that is comparable to that of the standard drug camptothecin. The compounds were also evaluated for their cytotoxic effect in four highly aggressive human cancer cell lines, namely KB, MDA-MB231 (breast), LNCap (prostate), and HT1080 (fibrosarcoma). Some of the compounds obtained showed promising cytotoxicities for these four cell lines.

Synthesis, Spectroscopic, X-ray Diffraction and DFT Studies of Novel Benzimidazole Fused-1,4-Oxazepines

A series of benzimidazole-tethered oxazepine heterocyclic hybrids has been synthesized in good to excellent yields from an N-alkylated benzimidazole 2-carboxaldehyde, which in turn was accomplished from o-phenylenediamine in three good yielding steps. The calculated molecular structure of compounds 2-methyl-4-(2-((phenylimino)methyl)-1H-benzo-[d]imidazol-1-yl)-butan-2-ol 9 and 10 3,3-dimethyl-N-phenyl-1,2,3,5-tetrahydrobenzo-[4,5]imidazo[2,1-c][1,4]oxazepin-5-amine using the B3LYP/6-31 G(d, p) method were found to agree well with their X-ray structures. The charge distributions at the different atomic sites were computed using the natural bond orbital (NBO) method. The regions of electrophilic and nucleophilic reactivity were shown using a molecular electrostatic potential (MEP) map. In addition, the frontier molecular orbitals of these compounds were discussed at the same level of theory. Nonlinear optical (NLO) properties have also been investigated by computational hyperpolarizability studies, and it was found that Compound 9 is the best candidate for NLO applications.

Novel routes to quinoline derivatives from N-propargylamines

A walk around the new avenue to the synthesis of quinoline derivatives from N-propargylamines.