Reactivity and stereoselectivity of oxazolopyridines with a ring‐junction nitrogen atom

Fused Nitrogen Bridgehead N,O-Acetals as Versatile Scaffolds: Synthetic Strategies, Mechanism and Applications

Fused Bicyclic N,O-acetals, are prominently present in several natural products and constitute a versatile family of compounds, with nitrogen-bridgehead fused N,O-bicyclic derivatives receiving specific emphasis as pivotal scaffolds due to their significant role in the bioactivity of medicinally relevant molecules. Hence, significant advancements in their applications in Organic Synthesis have been extensively documented in the literature, highlighting their role as key synthetic building blocks/motifs in the construction of complex organic molecules and their utility as chiral auxiliaries in the enantioselective synthesis of natural products and synthetic compound libraries. Nonetheless, while these developments have been well-explored, our review offers a new perspective by consolidating and critically evaluating various synthetic strategies for accessing the nitrogen-bridgehead fused N,O-acetal frameworks (such as hydropyrrolo-oxazole and oxazine frameworks) providing new insights into their mechanistic approaches and applications, and demonstrating their full potential in advanced synthetic chemistry. These methodologies are systematically covered in terms of their mechanistic pathways, synthetic efficiency, and practical applications, providing an integrated understanding of their contribution to the field of Organic Synthesis.

p-TSA catalyzed 6-endo-trig/dig cyclization of 5-aminopyrazoles and 3°/2°-propargylic alcohols: access to pyrazolo[1,5-a]dihydropyrimidines and pyrazolo[3,4-b]pyridines

A facile, straightforward synthesis of fused pyrazolo[1,5-a]dihydropyrimidines and pyrazolo[3,4-b]pyridines is accomplished by using 5-aminopyrazoles, 3°/2°-propargylic alcohols and ynones in the presence of p-TSA. The reaction proceeds through allenylation (N-alkylation)/propargylation (C-alkylation) of 5-aminopyrazoles, followed by intramolecular 6-endo-trig/dig cyclization leading to the title products with the formation of new C-N and C-C bonds. Operationally simple reaction conditions, inexpensive reagents, better yields, and gram-scale synthesis are the advantages of this protocol.

Synthesis and biological activities of bicyclic pyridines integrated steroid hybrid

Reports on structural modification of heterosteroids through various reactions, and developed synthetic routes have considerably increased over the last decade. The present review encompasses the applicable approaches dealing with the utility of reactive moieties in various steroids for the synthesis of fused bicyclic pyridines, and binary bicyclic pyridines all over the years. The different sections include the synthesis of steroids-fused, and binary quinolines, pyridopyrimidines, imidazopyridines, spirocyclic imidazopyridines, pyrazolopyridines, thienopyridines, pyridinyl-thiazoles, and tetrazolopyridine hybrids, as well as, the diverse biological applications of these heterocyclic steroids. The researchers' interest was principally focused on investigating the flexibility of synthetic strategies for various derivatives of natural steroids and building proposals based on heterocyclic steroids for drug discovery, biological assessments, and synthetic applications.

Synthesis, biological activities, and future perspectives of steroidal monocyclic pyridines

Steroidal pyridines are a class of compounds that have been the subject of extensive research in recent years due to their potential biological activities. The introduction of a pyridine ring into the steroid skeleton can significantly alter the chemical and biological properties of the compound, making it more potent and/or selective for a particular target. Different synthetic methods have been developed for the preparation of steroidal pyridines. This review provides an overview of the synthesis, biological activities, and future perspectives of steroidal monocyclic dihydropyridines, tetrahydropyridines, and pyridines from 2005 to the present. The different synthetic methods that have been developed for the preparation of these steroids are discussed, as well as the proposed mechanisms and the biological activities that have been reported. Finally, the potential of steroidal monocyclic pyridines for the development of new drugs is discussed. This review is intended to provide a comprehensive overview of the field of steroidal monocyclic pyridines for researchers and scientists who are interested in this area of research. It is also hoped that this review will stimulate further research into the synthesis and biological activities of steroidal pyridines to develop new and improved drugs for the treatment of diseases.

Advances on the biosynthesis of pyridine rings

Numerous studies have investigated the biosynthesis of pyridine heterocycles derived from nicotinic acid. However, metabolic pathways generating pyridine heterocycles in nature remain uninvestigated. Here, we summarize recent contributions conducted in the last decade on the biosynthetic pathways of non-derivate from nicotinic acid pyridine rings and discuss their implication on the study of natural products with pyridine structures.

Insights into the medicinal chemistry of heterocycles integrated with a pyrazolo[1,5-a]pyrimidine scaffold

Pyrazolo[1,5-a]pyrimidines are the dominant motif of many drugs; for instance, zaleplon and indiplon are sedative agents and ocinaplon was identified as an anxiolytic agent. The importance of this class of compounds lies in its varied and significant biological activities, and accordingly, considerable methods have been devised to prepare these compounds. Hence, other derivatives of this class of compounds were prepared by substitution reactions with different nucleophiles exploiting the activity of groups linked to the ring carbon and nitrogen atoms. The methods used vary through the condensation reactions of the aminopyrazoles with 1,2-allenic, enaminonitriles, enaminones, 1,3-diketones, unsaturated nitriles, or unsaturated ketones. Alternatively, these compounds are prepared through the reactions of acyclic reagents, as these methods were recently developed efficiently with high yields. The current review highlighted the recent progress of the therapeutic potential of pyrazolo[1,5-a]pyrimidines as antimicrobial, anticancer, antianxiety, anti-proliferative, analgesic, and antioxidant agents, carboxylesterase, translocator protein and PDE10A inhibitors, and selective kinase inhibitors.

Recent progress in the chemistry of β-aminoketones

The current study highlighted the significance of β-aminoketones as privileged biologically active molecules, recent synthetic strategies, and synthetic applications.

Bicyclic 5-6 Systems: Comprehensive Synthetic Strategies for the Annulations of Pyrazolo[ 1,5-a]pyrimidines

Pyrazolopyrimidines are a privileged class of 5-6 bicyclic systems with three or four nitrogen atoms, including four possible isomeric structures. The significance of this class of compounds is that they can be applied in medical and pharmaceutical fields due to their unlimited biological aptitude, hence it is the basic skeleton of several synthetic drugs. The current review aimed to highlight all the synthetic routes that have been applied to construct the pyrazolo[1,5-a]pyrimidine ring systems up to date. The sections in this study included the synthesis of pyrazolo[1,5- a]pyrimidines by condensation reactions of 5-aminopyrazoles with each of β-diketones, 1,5-diketones, β- ketoaldehydes, α-cyanoaldehydes, β-enaminones, enamines, enaminonitriles, ethers, with unsaturated ketones, unsaturated thiones, unsaturated esters, unsaturated dienones "1,2-allenic", unsaturated aldehydes, unsaturated imines, and unsaturated nitriles. The routes adopted to synthesize this class of heterocyclic compounds were extended for ring construction from acyclic reagents and multicomponent reactions under catalytic or catalyst-free conditions.