15N-Labelling and structure determination of adamantylated azolo-azines in solution

Trifluoromethyl-β-dicarbonyls as Versatile Synthons in Synthesis of Heterocycles

Trifluoromethyl group relishes a privileged position in the realm of medicinal chemistry because its incorporation into organic molecules often enhances the bioactivity by altering pharmacological profile of molecule. Trifluoromethyl-β-dicarbonyls have emerged as pivotal building blocks in synthetic organic chemistry due to their facile accessibility, stability and remarkable versatility. Owing to presence of nucleophilic and electrophilic sites, they offer multifunctional sites for the reaction. This review covers a meticulous exploration of their multifaceted role, encompassing an in-depth analysis of mechanism, extensive scope, limitations and wide-ranging applications in diverse organic synthesis, covering the literature from the 21st century. This comprehensive review encapsulates the applications of trifluoromethyl-β-dicarbonyls and their synthetic equivalents as precursors of complex and diverse heterocyclic scaffolds, fused heterocycles and spirocyclic compounds having medicinal and material importance. Their potent synthetic utility in cyclocondensation reactions with binucleophiles, cycloaddition reactions, C-C bond formations, asymmetric multicomponent reactions using classical/solvent-free/catalytic synthesis have been presented. Influence of unsymmetrical trifluoromethyl-β-diketones on regioselectivity of transformation is also reviewed. This review will benefit the synthetic and pharmaceutical communities to explore trifluoromethyl-β-dicarbonyls as trifluoromethyl building blocks for fabrication of heterocyclic scaffolds having implementation into drug discovery programs in the imminent future.

Iridium-Catalyzed Migratory Terminal C(sp3)-H Amidation of Heteroatom-Substituted Internal Alkenes via Olefin Chain Walking

Hydroamination facilitated by metal hydride catalysis is an appealing synthetic approach to access valuable nitrogen-containing compounds from readily available unsaturated hydrocarbons. While high regioselectivity can be achieved usually for substrates bearing polar chelation groups, the reaction involving simple alkenes frequently provides nonselective outcomes. Herein, we report an iridium-catalyzed highly regioselective terminal C(sp3)-H amidation of internal alkenes utilizing dioxazolones as an amino source via olefin chain walking. Most notably, this mechanistic motif of double bond migration to the terminal position operates not only with dialkyl-substituted simple alkenes including styrenes but also with heteroatom-substituted olefins such as enol ethers, vinyl silanes, and vinyl borons, thus representing the first example of the terminal methyl amidation of the latter type of alkenes through a nondissociative chain walking process.

The use of nitrogen-15 in microbial natural product discovery and biosynthetic characterization

This mini-review covers the use of nitrogen-15 in bacterial and fungal natural product discovery and biosynthetic characterization from 1970 to 2022. Nitrogen is an important element in a number of bioactive and structurally intriguing natural products including alkaloids, non-ribosomal peptides, and hybrid natural products. Nitrogen-15 can be detected at natural abundance utilizing two-dimensional nuclear magnetic resonance and mass spectrometry. Additionally, it is a stable isotope that can be added to growth media for both filamentous fungi and bacteria. With stable isotope feeding, additional two-dimensional nuclear magnetic resonance and mass spectrometry strategies have become available, and there is a growing trend to use nitrogen-15 stable isotope feeding for the biosynthetic characterization of natural products. This mini-review will catalog the use of these strategies, analyze the strengths and weaknesses of the different approaches, and suggest future directions for the use of nitrogen-15 in natural product discovery and biosynthetic characterization.

Mesomeric Betaines Based on Adamantylated 1,2,4-Triazolo[4,3-a]pyrimidin-5-ones: Synthesis, Structure and Conversion into Anionic N-Heterocyclic Carbenes

The C-N coupling of 1,2,4-triazolo[1,5-a]pyrimidin-7-ones with 1-adamantanol/1-bromoadamantane leads to 1,2,4-triazolo[4,3-a]pyrimidinium-5-olates, which are represented as mesomeric betaines (MBs). The formation of MBs involves not only N-alkylation of heterocyclic framework but also the rearrangement leading to a change in the type of fusion between pyrimidine and 1,2,4-triazole fragments. The structures of the obtained products were confirmed by the X-ray analysis and measurements of ¹³ C-¹³ C (J_CC ) coupling constants in the 1D ¹³ C NMR spectra of selectively ¹³ C-labeled samples. Treatment of the betaines with lithium bis(trimethylsilyl)amide (LiHMDS) gave anionic carbenes, which were detected by ¹³ C NMR spectroscopy and were trapped by reactions with phenyl isothiocyanate and sulfur. Density functional theory (DFT) and the quantum theory of atoms in molecules (QTAIM) analyses allowed for an insight into the electronic structure of the obtained betaines and N-heterocyclic carbene derivatives.

Photoinduced Transition-Metal-Free Chan-Evans-Lam-Type Coupling: Dual Photoexcitation Mode with Halide Anion Effect

Herein, we report a photoinduced transition-metal-free C(aryl)-N bond formation between 2,4,6-tri(aryl)boroxines or arylboronic acids as an aryl source and 1,4,2-dioxazol-5-ones (dioxazolones) as an amide coupling partner. Chloride anion, either generated in situ by photodissociation of chlorinated solvent molecules or added separately as an additive, was found to play a critical cooperative role, thereby giving convenient access to a wide range of synthetically versatile N-arylamides under mild photo conditions. The synthetic virtue of this transition-metal-free Chan-Evans-Lam-type coupling was demonstrated by large-scale reactions, synthesis of ¹⁵N-labeled arylamides, and applicability toward biologically relevant compounds. On the basis of mechanistic investigations, two distinctive photoexcitations are proposed to function in the current process, in which the first excitation involving chloro-boron adduct facilitates the transition-metal-free activation of dioxazolones by single electron transfer (SET), and the second one enables the otherwise-inoperative 1,2-aryl migration of the thus-formed N-chloroamido-borate adduct.

Synthetic approaches to 1,2,4-triazolo[5,1-c][1,2,4]triazin-7-ones as basic heterocyclic structures of the antiviral drug Riamilovir ("Triazavirin®") active against SARS-CoV-2 (COVID-19)

Fragments of 1,2,4-triazolo[5,1-c][1,2,4]triazin-7-one are found in many compounds with various types of biological activities, including the antiviral drug Riamilovir (Triazavirin®), which shows activity against SARS-CoV-2 (COVID-19). Therefore, the development of convenient methods for the synthesis of new derivatives of 1,2,4-triazolo[5,1-c][1,2,4]triazin-7-one is always in demand. This review systematizes the information on the most common synthetic methods for constructing the 1,2,4-triazolo[5,1-c][1,2,4]triazin-7-one heterocyclic system.

Enantioselective Synthesis of Chiral Substituted 2,4-Diketoimidazolidines and 2,5-Diketopiperazines via Asymmetric Hydrogenation

An enantioselective hydrogenation of 5-alkylidene-2,4-diketoimidazolidines (hydantoins) and 3-alkylidene-2,5-ketopiperazines catalyzed by the Rh/f-spiroPhos complex under mild conditions has been developed, which provides an efficient approach to the highly enantioselective synthesis of chiral hydantoins and 2,5-ketopiperazine derivatives with high enantioselectivities up to 99.9% ee.

15N labeling and analysis of 13C–15N and 1H–15N couplings in studies of the structures and chemical transformations of nitrogen heterocycles

This review provides a generalization of effective examples of ¹⁵N labeling followed by an analysis of J_CN and J_HN couplings in solution as a tool to study the structural aspects and pathways of chemical transformations in nitrogen heterocycles.