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Piperazine ranks as the third most common nitrogen heterocycle in drug discovery, and it is the key component of several blockbuster drugs, such as Imatinib (also marketed as Gleevec) or Sildenafil, sold as Viagra. Despite its wide use in medicinal chemistry, the structural diversity of piperazines is limited, with about 80% of piperazine-containing drugs containing substituents only at the nitrogen positions. Recently, major advances have been made in the C–H functionalization of the carbon atoms of the piperazine ring. Herein, we present an overview of the recent synthetic methods to afford functionalized piperazines with a focus on C–H functionalization.

A catalytic domino reduction–imine formation–intramolecular cyclization–oxidation for the general synthesis of a wide variety of biologically relevant N‐polyheterocycles, such as quinoxaline‐ and quinoline‐fused derivatives, and phenanthridines, is reported. A simple, easily available, and environmentally friendly dioxomolybdenum(VI) complex has proven to be a highly efficient and versatile catalyst for transforming a broad range of starting nitroarenes involving several redox processes. Not only is this a sustainable, step‐economical as well as air‐ and moisture‐tolerant method, but also it is worth highlighting that the waste byproduct generated in the first step of the sequence is recycled and incorporated in the final target molecule, improving the overall synthetic efficiency. Moreover, selected indoloquinoxalines have been photophysically characterized in cyclohexane and toluene with exceptional fluorescence quantum yields above 0.7 for the alkyl derivatives., A catalytic domino reduction / imine formation / intramolecular cyclization / oxidation allows the synthesis of a wide variety of biologically relevant N‐polyheterocycles. The reported process employs an inexpensive and nontoxic dioxomolybdenum(VI) complex as catalyst, easily available nitroarenes as starting materials and different glycols as reducing agents with reuse of the waste reduction carbonyl byproduct, which is embodied into the final compounds.

This article describes the application of N‐heterocyclic iod(az)olium salts (NHISs) as highly reactive organocatalysts. A variety of mono‐ and dicationic NHISs are described and utilized as potent XB‐donors in halogen‐bond catalysis. They were benchmarked in seven diverse test reactions in which the activation of carbon‐ and metal‐chloride bonds as well as carbonyl and nitro groups was achieved. N‐methylated dicationic NHISs rendered the highest reactivity in all investigated catalytic applications with reactivities even higher than all previously described monodentate XB‐donors based on iodine(I) and (III) and the strong Lewis acid BF3., N‐Heterocyclic iod(az)olium salts are introduced as highly potent halogen bonding (XB) organocatalysts reactivity in diverse test reactions based on the activation of halides and neutral species. Especially, N‐methylated, dicationic derivatives outperformed all known monodentate iodine(I) and (III) XB‐donors as well as the strong Lewis acid BF3.

In-situ-generated N-aryl nitrile imines derived from trifluoroacetonitrile efficiently react with polycyclic 1,4-quinones, yielding fused pyrazole derivatives as the exclusive products. The reactions proceed via the initially formed [3 + 2]-cycloadducts, which undergo spontaneous aerial oxidation to give aromatized heterocyclic products. Only for 2,3,5,6-tetramethyl-1,4-benzoquinone, the expected [3 + 2]-cycloadduct exhibited fair stability and could be isolated in moderate yield (53%). The presented method offers a straightforward access to hitherto little known trifluoromethylated polycyclic pyrazoles. All products were isolated as pale colored solids with medium-intensity absorption maxima in the range of 310–340 nm for naphthoquinone-derived products and low-intensity bands in the visible region (≈400 nm) for the anthraquinone series.

The tandem gold(I)-catalyzed rearrangement/Nazarov reaction of enynyl acetates in which the double bond is embedded in a piperidine ring was computationally and experimentally studied. The theoretical calculations predict that the position of the propargylic acetate substituent has a great impact on the reactivity. In contrast to our previous successful cyclization of the 2-substituted substrates, where the nitrogen favors the formation of the cyclized final product, the substitution at position 3 was computed to have a deleterious effect on the electronic properties of the molecules, increasing the activation barriers of the Nazarov reaction. The sluggish reactivity of 3-substituted piperidines predicted by the calculations was further confirmed by the results obtained with some designed substrates.

Stereoselective organocatalytic C–C bond formations that tolerate N‐heterocycles are valuable since these moieties are common motifs in numerous chiral bioactive compounds. Such transformations are, however, challenging since N‐heterocyclic moieties can interfere with the catalytic reaction. Here, we present a peptide that catalyzes conjugate addition reactions between aldehydes and nitroolefins bearing a broad range of different N‐heterocyclic moieties with basic and/or H‐bonding sites in excellent yields and stereoselectivities. Tuning of the pyramidalization direction of the enamine intermediate enabled the high stereoselectivity. © WILEY 2020 ISSN:0947-6539 ISSN:1521-3765

Benzazetidines are a class of N-heterocycles potentially very interesting for a variety of purposes, including biological applications and drug design. In the past, their high ring strain has hampered the development of trustable, general, and efficient synthetic methodologies for their preparation. In this review article, the aim is to disclose all the literature contributions about the synthesis of these compounds and the study of their reactivity, from the early examples to the most recent synthetic approaches. Recently, there has been a growth of interest for this heterocycle, driven by the publication of novel synthetic methodologies based on palladium-catalyzed intramolecular C-H amination and organocatalyzed ring-closure of 2-(N-Boc-anilino)-α-ketoesters/amides.

International audience; Palladium catalysts supported on acidic fluorinated magnesium hydroxide Pd/MgF2x(OH)x were prepared through precipitation or impregnation methods. Applications to the hydrogenation of various aldimines and ketimines resulted in good catalytic activities at mild temperatures using one atmosphere of hydrogen. Quinolines, pyridines and other Nheterocycles were successfully hydrogenated at higher temperature and hydrogen pressure using low palladium loadings and without the use of any acid additive. Such reactivity trend confirmed the positive effect of the Brønsted and Lewis acid sites from the fluorinated magnesium hydroxide support resulting in the effective pre-activation of N-heterocycle substrates and therefore in the good catalytic activity of the palladium nanoparticles during the hydrogenations. As demonstrated in the hydrogenation of imines, the catalyst was recycled up to 10 times without either loss of activity or palladium leaching.

N-heterocycles, both saturated and unsaturated, are ubiquitous biologically active molecules that are extremely appealing scaffolds in drug discovery programs. Although classical synthetic methods have been developed to access many relevant N-heterocyclic scaffolds, representing well-established and reliable routes, some do not meet the needs of sustainability. In this context, several advances have been made towards the sustainable synthesis of N-heterocycles. This review focuses on the most recent examples from the last five years of catalytic synthesis of several heterocyclic compounds of medicinal relevance. Thus, the synthesis of isoindoloquinazolines, quinazolines and azaindoles, among others, are covered. The synthetic methods selected include the use of homogeneous and heterogeneous catalysts and the use of alternative and sustainable methods such as, for example, metal-catalyzed acceptorless coupling and one-pot reactions. The green aspects of the individual synthetic approaches are highlighted, and the scope of each methodology is described.

Made available in DSpace on 2019-10-06T17:10:16Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-08-15 Fundação para a Ciência e a Tecnologia We report the design, synthesis and biological studies on a group of mixed ligand Fe(III) complexes as anti-cancer drug candidates, namely their interaction with DNA, cytotoxicity and mechanism(s) of action. The aim is to obtain stable, efficient and selective Fe-complexes to be used as anti-cancer agents with less damaging side effects than previously reported compounds. Five ternary Fe(III) complexes bearing a tripodal aminophenolate ligand L2−, H2L = N,N-bis(2-hydroxy-3,5-dimethylbenzyl)-N-(2-pyridylmethyl)amine, and different aromatic bases NN = 2,2′-bipyridine [Fe(L)(bipy)]PF6 (1), 1,10-phenanthroline [Fe(L)(phen)]PF6 (2), or a phenanthroline derivative co-ligand: [Fe(L)(amphen)]NO3 (3), [Fe(L)(amphen)]PF6 (3a), [Fe(L)(Clphen)]PF6 (4), [Fe(L)(epoxyphen)]PF6 (5) (where amphen = 1,10-phenanthroline-5-amine, epoxyphen = 5,6-epoxy-5,6-dihydro-1,10-phenanthroline, Clphen = 5-chloro-1,10-phenanthroline) and the [Fe(L)(EtOH)]NO3 (6) complex are synthesized. The compounds are characterized in the solid state and in solution by elemental analysis, ESI-MS, magnetic susceptibility measurements and FTIR, UV–Vis, 1H and 13C NMR and fluorescence spectroscopies. [Fe(phen)Cl3] and [Fe(amphen)Cl3] were also prepared for comparison purposes. Spectroscopic binding studies indicate groove binding as the main interaction for most complexes with DNA, and for those containing amphen a B- to Z-DNA conformational change is proposed to occur. As determined via MTT analysis all compounds 1–6 are cytotoxic against a panel of three different cell lines (HeLa, H1299, MDA-MB-231). For selected compounds with promising cytotoxic activity, apoptosis was evaluated using cell and DNA morphology, TUNEL, Annexin V/7AAD staining and caspase3/7 activity. The compounds induce oxidative DNA damage on plasmid DNA and in cell culture as assessed by 8-oxo-Guanine and γH2AX staining. Comet assay confirmed the presence of genomic damage. There is also increased reactive oxygen species formation following drug treatment, which may be the relevant mechanism of action, thus differing from that normally assumed for cisplatin. The Fe(III)-complexes were also tested against strains of M. Tuberculosis (MTb), complex 2 depicting higher anti-MTb activity than several known second line drugs. Hence, these initial studies show prospective anti-cancer and anti-MTb activity granting promise for further studies. Centro de Química Estrutural Departamento de Engenharia Química Instituto Superior Técnico Universidade de Lisboa, Av. Rovisco Pais 1 TUBITAK Marmara Research Center Genetic Engineering and Biotechnology Institute, Gebze Koc University Research Center for Translational Medicine (KUTTAM), Sariyer Koc University Medical School, Sariyer Adnan Menderes University School of Medicine BioISI Faculdade de Ciências Universidade de Lisboa, Lisboa Department of Physics University of Coimbra Centro de Química e Bioquímica Faculdade de Ciências Universidade de Lisboa, Lisboa Faculdade de Ciências Farmacêuticas UNESP, C.P.582, SP Centro de Quimica Estrutural Faculdade de Ciências Universidade de Lisboa, Lisboa Faculdade de Ciências Farmacêuticas UNESP, C.P.582, SP Fundação para a Ciência e a Tecnologia: IF/01179/2013 Fundação para a Ciência e a Tecnologia: RECI/QEQ-MED/0330/2012 Fundação para a Ciência e a Tecnologia: RECI/QEQ-QIN/0189/2012 Fundação para a Ciência e a Tecnologia: UID/BIO/04565/2013 Fundação para a Ciência e a Tecnologia: UID/MULTI/04349/2013 Fundação para a Ciência e a Tecnologia: UID/QUI/00100/2013

The fate of the green plant pigment chlorophyll (Chl) in de‐greening leaves has long been a fascinating biological puzzle. In the course of the last three decades, various bilin‐type products of Chl breakdown have been identified, named phyllobilins (PBs). Considered ‘mere’ leftovers of a controlled biological Chl detoxification originally, the quest for finding relevant bioactivities of the PBs has become a new paradigm. Indeed, the PBs are abundant in senescent leaves, in ripe fruit and in some vegetables, and they display an exciting array of diverse heterocyclic structures. This review outlines briefly which types of Chl breakdown products occur in higher plants, describes basics of their bio‐relevant structural and chemical properties and gives suggestions as to ‘why’ the plants produce vast amounts of uniquely ‘decorated’ heterocyclic compounds. Clearly, it is worthwhile to consider crucial metabolic roles of PBs in plants, which may have practical consequences in agriculture and horticulture. However, PBs are also part of our plant‐based nutrition and their physiological and pharmacological effects in humans are of interest, as well.

RECENT ADVANCES IN SELECTIVE FUNCTIONALIZATION OF QUINOLINES. Heterocyclic compounds form an important and extensive group of organic substances. Among nitrogenous heterocyclic molecules, quinolines stand out for exhibiting attractive chemical and biological properties. These substances can be used as ligands, sensors, luminescent and agrochemical materials. In addition, quinoline-containing compounds can exhibit a wide spectrum of pharmacological properties, allowing their use in several approved drugs nowadays. Due to its importance, the synthesis of molecules containing this nucleus becomes a point of interest for synthetic chemists. In this way, several methodologies have been recently developed to prepare quinoline derivatives with high structural diversity. Such chemical transformations allow the chemical modification of these rings with high selectivity and tolerance to diverse functional groups and these properties have been conveniently used in the preparation of biologically active molecules containing this unit. Herein, we present a review of the main methodologies employed in the selective functionalization of quinolines in the last twenty years. In this context, a brief introduction addressing general synthetic and medicinal aspects related to the functionalization positions of the quinoline ring is presented. Several methodologies used in the functionalization of this moiety are discussed, as well relevant synthetic applications, both in the preparation and functionalization of substances of biological interest.

Dibenzo[hi,st]ovalene (DBOV) has excellent photophysical properties, including strong fluorescence and high ambient stability. Moreover, the optical blinking properties of DBOV have enabled optical super-resolution single-molecule localization microscopy with an imaging resolution beyond the diffraction limit. Various organic and inorganic fluorescent probes have been developed for super-resolution imaging, but those sensitive to pH and/or metal ions have remained elusive. Here, we report a diaza-derivative of DBOV (N-DBOV), synthesized in eight steps with a total yield of 15%. Nitrogen (N)-bearing zigzag edges were formed through oxidative cyclization of amino groups in the last step. UV-vis and fluorescence spectroscopy of N-DBOV revealed its promising optical properties comparable to those of the parent DBOV, while cyclic voltammetry and density functional theory calculations highlighted its lower orbital energy levels and potential n-type semiconductor character. Notably, in contrast to that of the parent DBOV, the strong luminescence of N-DBOV is dependent on pH and the presence of heavy metal ions, indicating the potential of N-DBOV in sensing applications. N-DBOV also exhibited pH-responsive blinking, which enables pH-sensitive super-resolution imaging. Therefore, N-DBOV appears to be a highly promising candidate for fluorescence sensing in biology and environmental analytics.

Summary The Povarov reaction, a formal [4 + 2] cycloaddition between N-aryl imines and electron-rich dienophiles, has been defined as an efficient method to approach tetrahydroquinolines and has been well established in the past decades. In general, electron-rich heterosubstituted alkenes have served as the most popular dienophiles to achieve the exclusive regioselectivity. However, the use of Lewis acids and Bronsted acids as catalysts is required in these transformations, and, to our knowledge, the Povarov reaction of electron-rich heterosubstituted alkynes has not been reported. Here, we disclose a catalyst-free Povarov reaction of formyl-ynamides with anilines for the rapid and practical synthesis of a diverse range of valuable quindolines, which not only represents the first Povarov reaction of ynamides to the best of our knowledge but also constitutes a very rare example of a catalyst-free ynamide cyclization reaction. This formal [1 + 2 + 3] annulation shows a reversed regioselectivity compared with the previous protocols.

Pyrazolothiazole-substituted pyridine conjugates are an important class of heterocyclic compounds with an extensive variety of potential applications in the medicinal and pharmacological arenas. Therefore, herein, we describe an efficient and facile approach for the synthesis of novel pyrazolo-thiazolo-pyridine conjugate 4, via multicomponent condensation. The latter compound was utilized as a base for the synthesis of two series of 15 novel pyrazolothiazole-based pyridine conjugates (5–16). The newly synthesized compounds were fully characterized using several spectroscopic methods (IR, NMR and MS) and elemental analyses. The anti-proliferative impact of the new synthesized compounds 5–13 and 16 was in vitro appraised towards three human cancer cell lines: human cervix (HeLa), human lung (NCI-H460) and human prostate (PC-3). Our outcomes regarding the anti-proliferative activities disclosed that all the tested compounds exhibited cytotoxic potential towards all the tested cell lines with IC50 = 17.50–61.05 µM, especially the naphthyridine derivative 7, which exhibited the most cytotoxic potential towards the tested cell lines (IC50 = 14.62–17.50 µM) compared with the etoposide (IC50 = 13.34–17.15 µM). Moreover, an in silico docking simulation study was performed on the newly prepared compounds within topoisomerase II (3QX3), to suggest the binding mode of these compounds as anticancer candidates. The in silico docking results indicate that compound 7 was a promising lead anticancer compound which possesses high binding affinity toward topoisomerase II (3QX3) protein.

Thecatalytic properties of graphene-derived materials are evaluated in acceptorless dehydrogenation of N-heterocycles. Among them, reduced graphene oxides (rGOs) are active (quantitative yields in 23 h) under mild conditions (130 °C) and act as efficient heterogeneous carbocatalysts. rGO exhibits reusability and stability at least during eight consecutive runs. Mechanistic investigations supported by experimental evidence (i.e., organic molecules as model compounds, purposely addition of metal impurities and selective functional group masking experiments) suggest a preferential contribution of ketone carbonyl groups as active sites for this transformation., Supported by MCIN/AEI/10.13039/501100011033/FEDER (Grant Nos. RTI2018-098237-B-C21, RTI2018-098237-B-C22, and PID2019-105881RB-I00), Generalitat Valenciana (No. PROMETEU/2020/028), and Universitat Jaume I (No. UJI-B2018-23).

Pentacyclic triterpenoids are well-known phytochemicals with various biological activities commonly found in plants as secondary metabolites. The wide range of biological activities exhibited by triterpenoids has made them the most valuable sources of pharmacological agents. A number of novel triterpenoid derivatives with many skeletal modifications have been developed. The most important modifications are the formation of analogues or derivatives with nitrogen-containing heterocyclic scaffolds. The derivatives with nitrogen-containing heterocyclic compounds are among the most promising candidate for the development of novel therapeutic drugs. About 75% of FDA-approved drugs are nitrogen-containing heterocyclic moieties. The unique properties of heterocyclic compounds have encouraged many researchers to develop new triterpenoid analogous with pharmacological activities. In this review, we discuss recent advances of nitrogen-containing heterocyclic triterpenoids as potential therapeutic agents. This comprehensive review will assist medicinal chemists to understand new strategies that can result in the development of compounds with potential therapeutic efficacy.

Oxide is an attractive linker for building polymetallic complexes that provide molecular models for metal oxide activity, but studies of these systems are limited to metals in high oxidation states. Herein, we synthesized and characterized the molecular and electronic structure of diuranium bridged U-III/U-IV and U-III/U-III complexes. Reactivity studies of these complexes revealed that the U-O bond is easily broken upon addition of N-heterocycles resulting in the delivery of a formal equivalent of U-III and U-II, respectively, along with the uranium(IV) terminal-oxo coproduct. In particular, the U-III/U-III oxide complex effects the reductive coupling of pyridine and two-electron reduction of 4,4 '-bipyridine affording unique examples of diuranium(III) complexes bridged by N-heterocyclic redox-active ligands. These results provide insight into the chemistry of low oxidation state metal oxides and demonstrate the use of oxo-bridged U-III/U-III complexes as a strategy to explore U-II reactivity.

Perimidines are versatile scaffolds and a fascinating class of N-heterocycles that have evolved significantly in recent years due to their immense applications in life sciences, medical sciences, and industrial chemistry. Their ability of molecular interaction with different proteins, complex formation with metals, and distinct behavior in various ranges of light makes them more appealing and challenging for future scientists. Various novel technologies have been developed for the selective synthesis of perimidines and their conjugated derivatives. These methods extend to the preparation of different bioactive and industrially applicable molecules. This review aims to present the most recent advancements in perimidine synthesis under varied conditions like MW radiation, ultrasound, and grinding using different catalysts such as ionic liquids, acid, metal, and nanocatalyst and also under green environments like catalyst and solvent-free synthesis. The applications of perimidine derivatives in drug discovery, polymer chemistry, photo sensors, dye industries, and catalytic activity in organic synthesis are discussed in this survey. This article is expected to be a systematic, authoritative, and critical review on the chemistry of perimidines that compiles most of the state-of-art innovation in this area. Graphic Abstract

Tetraaza-macrocyclic pyridinophane L-Ts, decorated with a p-toluenesulfonyl (tosyl, Ts) group, appear to be a useful tool to provide evidence on how the interplay of various supramolecular forces can help stabilise exotic anionic species such as tribromide (Br3&minus, ) anions. Indeed, crystals of (H2L-Ts)(Br3)1.5(NO3)0.5 unexpectedly grew from an acidic (HNO3) aqueous solution of L-Ts in the presence of Br&minus, anions. The crystal structure of this compound was determined by single crystal XRD analysis. Hydrogen bonds, salt-bridges, anion-, - stacking, and van der Waals interactions contribute to stabilising the crystal lattice. The observation of two independent Br3&minus, anions stuck over the &pi, electron densities of pyridine and tosyl ligand groups, one of them being sandwiched between two pyridine rings, corroborates the significance of anion-&pi, interactions for N-containing heterocycles. We show herein the possibility of detecting anion-&pi, contacts from fingerprint plots generated by Hirshfeld surface analysis, demonstrating the effective usage of this structural investigation technique to further dissect individual contributions of stabilising supramolecular forces.

New porphyrin-imidazole derivatives were synthesised by Radziszewski reaction between 2-formyl-5,10,15,20-tetraphenylporphyrin 1 and several (hetem)aromatic 1,2-diones, which after cationization afforded promising monocationic photosensitizers 3a-d. Singlet oxygen studies have demonstrated that all the cationic porphyrin-imidazole conjugates 3a-d were capable to produce cytotoxic species. These photosensitizers were able to photoinactivate Eschericha coli and their inactivation profile was improved in the presence of KI., The authors are grateful to University of Aveiro and FCT/MCT for the financial support for QOPNA research Unit (FCT UID/QUI/00062/2019), the LAQV-REQUIMTE (UIDB/50006/2020), CESAM (UID/AMB/50017/2019) and CQUM (QUI/UI0686/2018) through national founds and, where applicable, co-financed by the FEDER, within the PT2020 Partnership Agreement, and to the Portuguese NMR Network. The research contract of N.M.M. Moura (REF.-048-88-ARH/2018) is funded by national funds (OE), through FCT - Fundacao para a Ciencia e a Tecnologia, I.P., in the scope of the framework contract foreseen in the numbers 4, 5 and 6 of the article 23, of the Decree-Law 57/2016, of August 29, changed by Law 57/2017, of July 19.

The novel coronavirus, COVID-19, caused by SARS-CoV-2, is a global health pandemic that started in December 2019. The effective drug target among coronaviruses is the main protease Mpro, because of its essential role in processing the polyproteins that are translated from the viral RNA. In this study, the bioactivity of some selected heterocyclic drugs named Favipiravir (1), Amodiaquine (2), 2&prime, Fluoro-2&prime, deoxycytidine (3), and Ribavirin (4) was evaluated as inhibitors and nucleotide analogues for COVID-19 using computational modeling strategies. The density functional theory (DFT) calculations were performed to estimate the thermal parameters, dipole moment, polarizability, and molecular electrostatic potential of the present drugs, additionally, Mulliken atomic charges of the drugs as well as the chemical reactivity descriptors were investigated. The nominated drugs were docked on SARS-CoV-2 main protease (PDB: 6LU7) to evaluate the binding affinity of these drugs. Besides, the computations data of DFT the docking simulation studies was predicted that the Amodiaquine (2) has the least binding energy (&minus, 7.77 Kcal/mol) and might serve as a good inhibitor to SARS-CoV-2 comparable with the approved medicines, hydroxychloroquine, and remdesivir which have binding affinity &minus, 6.06 and &minus, 4.96 Kcal/mol, respectively. The high binding affinity of 2 was attributed to the presence of three hydrogen bonds along with different hydrophobic interactions between the drug and the critical amino acids residues of the receptor. Finally, the estimated molecular electrostatic potential results by DFT were used to illustrate the molecular docking findings. The DFT calculations showed that drug 2 has the highest of lying HOMO, electrophilicity index, basicity, and dipole moment. All these parameters could share with different extent to significantly affect the binding affinity of these drugs with the active protein sites.

In search of unprecedented tri and/or tetrapod pharmacophoric conjugates, a series of 32 new 4-ethyl-1H-benzo[b][1,4]diazepin-2(3H)-ones were synthesized and properly elucidated using MS, IR, NMR, and elemental analysis. In vitro investigation of 11 compounds of this series, using a panel of two human tumor cell lines namely, human breast adenocarcinoma (MCF-7), and human colorectal carcinoma (HCT-116), revealed promising cytotoxic activities. Among all synthesized compounds, analogue 9 displayed maximum cytotoxicity with IC50 values of 16.19 &plusmn, 1.35 and 17.16 &plusmn, 1.54 &mu, M against HCT-116 and MCF-7, respectively, compared to standard drug doxorubicin.

Abstractsp2 Carbon-Hydrogen Bond (C-H) FunctionalizationbySirilata YotphanDoctor of Philosophy in ChemistryUniversity of California, BerkeleyProfessor Robert G. Bergman, ChairChapter 1. A review of the Bergman/Ellman group literature on rhodium-catalyzed direct sp2 C-H bond functionalization reactions is presented. In addition, some well-known late transition-metal catalyzed sp2 C-H bond functionalization reactions are described. These synthetic methods have valuable applications for organic chemistry and enable access to a number of interesting organic compounds and derivatives. These examples highlight the importance of this type of transformation and provide the background from which the results described in Chapters 2-5 may be viewed.Chapter 2. Bridgehead bicyclic unsaturated enamines were prepared by a tandem rhodium-catalyzed C-H bond activation/alkenylation/electrocyclization of alkyne-tethered unsaturated imines. These strained bicyclic enamines exhibit unique reactivity: for example, they lead to N-alkylated products upon treatment with alkylating reagents and undergo double bond isomerization to alleviate ring strain upon reduction.Chapter 3. An efficient method is reported for the preparation of multicyclic pyridines and quinolines by a rhodium-catalyzed intramolecular C-H bond functionalization process. The method shows good scope for branched and unbranched alkyl substituents on the pyridine ring and at the R position of the tethered alkene group. Starting materials capable of undergoing olefin isomerization to provide terminal 1,1-disubstituted alkenes also proved to be effective substrates.Chapter 4. A method for the direct arylation of benzotriazepines is reported, employing an aryl iodide as the coupling partner, copper iodide as the catalyst, and lithium tert-butoxide as the base. A variety of electron-rich, electron-poor, and sterically hindered aryl iodides are compatible with the reaction conditions. The arylation reaction can also be performed outside a glovebox in air without a significant decrease in yield. Furthermore, convenient microwave conditions for carrying out this transformation are reported.Chapter 5. The reaction of isopropyl Grignard reagent and 3-bromoquinoline leads to formation of interesting 3,4-disubstituted quinoline products in significant yields. This transformation was extensively studied for 3-bromoquinoline as the substrate, isopropyl magnesium chloride as the nucleophile, and a Brønsted acid or 3-bromopropene as electrophiles. A brief survey of this transformation, identification of the reaction limitations, and a suggested mechanism are reported in this Chapter.

Organic Letters, 19 (17), ISSN:1523-7060, ISSN:1523-7052

Coordination of FeCl3 to the redox-active pyridine–aminophenol ligand NNOH2 in the presence of base and under aerobic conditions generates FeCl2(NNOISQ) (1), featuring high-spin FeIII and an NNOISQ radical ligand. The complex has an overall S = 2 spin state, as deduced from experimental and computational data. The ligand-centered radical couples antiferromagnetically with the Fe center. Readily available, well-defined, and air-stable 1 catalyzes the challenging intramolecular direct C(sp3)–H amination of unactivated organic azides to generate a range of saturated N-heterocycles with the highest turnover number (TON) (1 mol% of 1, 12 h, TON = 62; 0.1 mol% of 1, 7 days, TON = 620) reported to date. The catalyst is easily recycled without noticeable loss of catalytic activity. A detailed kinetic study for C(sp3)–H amination of 1-azido-4-phenylbutane (S1) revealed zero order in the azide substrate and first order in both the catalyst and Boc2O. A cationic iron complex, generated from the neutral precatalyst upon reaction with Boc2O, is proposed as the catalytically active species.

Thiazoles and their hydrogenated analogues are not only key structural units in a wide variety of natural products but they also constitute important building blocks in medicinal chemistry. Therefore, the synthesis of these compounds using new protocols is always interesting. It is well known that N-propargylamines can undergo a number of cyclization reactions to produce various nitrogen-containing heterocycles. In this review, we highlight the most important developments on the synthesis of thiazole and its derivatives starting from N-propargylamines. This review will be helpful in the development of improved methods for the synthesis of natural and biologically important compounds.

Polynuclear silver(I) complex, [Ag(NO3-O)(2,2'-bq-N,N')]n, was synthesized by the reaction of equimolar amount of silver(I) nitrate and 2,2'-biquinoline (2,2'-bq) in ethanol at room temperature. The characterization of the complex was established on the basis of elemental microanalysis, IR, NMR (1H and 13C) and UV-Vis spectroscopic techniques. The results of spectroscopic analyses revealed that in [Ag(NO3-O)(2,2'-bq-N,N')]n complex, 2,2'-bq ligand behaves as a chelate, while the remaining coordination sites are occupied by the oxygen atoms of two nitrates.

Oxygen and nitrogen heterocyclic systems are present in a large number of natural and synthetic compounds. In particular, oxa- and aza-silacyclane, tetrahydrofuran, benzofuran, cycloheptadifuranone, cycloheptadipyrrolone, pyrrolidine, lactone, lactam, phthalan, isochromanone, tetrahydroisoquinolinone, benzoindolizidinone, indoline and indolizidine scaffolds are present in many classes of biologically active molecules. Most of these contain a C=O moiety which can be easily introduced using carbonylative reaction conditions. In this field, intramolecular silylformylation and silylcarbocyclization reactions may afford heterocyclic compounds containing a carbonyl functional group together with a vinylsilane moiety which can be further transformed. Considering these two aspects, in this review a detailed analysis of the literature data regarding the application of silylformylation and silylcarbocyclization reactions to the synthesis of several heterocyclic derivatives is reported.

Using purine as a scaffold, the methods for preparation of novel 2-aminopurine and purine derivatives substituted at position C6 by the fragments of natural amino acids, short peptides, andN-heterocycles, including enantiopure ones, have been proposed. The methods for determination of the enantiomeric purity of the obtained chiral compounds have been developed. Conjugates exhibiting high antimycobacterial or antiherpesvirus activity against both laboratory and multidrug-resistant strains were revealed among the obtained compounds. © 2020 De Gruyter. All rights reserved. Russian Science Foundation, RSF: 19-13-00231 Funding : The reviewed studies were financially supported by the Russian Science Foundation (project no. 19-13-00231).

A two-step palladium-catalyzed procedure based on Suzuki–Miyaura cross coupling, followed by a double Buchwald–Hartwig reaction, allows for the synthesis of pharmaceutically relevant benzo[4,5]furo[3,2-b]indoles in moderate to very good yield. The synthesized compounds have been analyzed with regard to their inhibitory activity (IC50) of nucleotide pyrophosphatases h-NPP1 and h-NPP3. The activity lies in the nanomolar range. The results were rationalized based on docking studies.

Nazarov tepkimesi beşli halkaların sentezinde kullanışlı bir sentetik yol olmasına rağmen, bu tepkimenin bir türevi olan ve N-heterosiklik bileşikler üreten aza-Nazarov tepkimeleri üzerine sınırlı sayıda çalışma bulunmaktadır. Aza-Nazarov tepkimesi için etkili ve ılımlı koşullar altında çalışan bir yöntem henüz geliştirilmemiştir. Azot atomu içeren heterosiklik bileşiklerin organik ve farmasötik kimyada önemi göz önüne alınınca, yeni bir aza-Nazarov tepkimesinin geliştirilmesi birçok sentetik kullanımda yararlı olacaktır. Bu çalışmada, 3,4-dihidroizokinolin ve α,β-doymamış açil klorür bileşikleri arasında yeni bir katalitik aza-Nazarov tepkimesi geliştirilmiştir. β-silikon kararlılık etkisi ve anyon değiştirme yönteminden faydalanılarak oluşturulan tepkime verim, tepkime koşulları ve çevre sorunları açısından çok daha uygun koşullar altında yürümektedir. İlk aşamada, akiral anyon değiştirme yönteminde anyon kaynağı olarak gümüş triflorometilsülfonat (AgOTf) kullanılmıştır. Tepkimenin geniş bir substrat aralığında çalıştığını göstermek için başlangıç maddelerinin bileşenleri elektron çekici ve verici gruplarla değiştirilerek denenmiştir. İlerleyen aşamalarda tepkimeyi enantioseçici yapmak amacıyla kiral katalizörler ile birçok deneme yapılmasına rağmen sonuçlar tatmin edici olamamıştır. Although Nazarov reaction is a synthetically useful route for the synthesis of five-membered rings, there are a very limited number of studies on its analogous process producing N-heterocycles; aza-Nazarov reaction, and an effective methodology that proceeds under mild conditions has yet to be developed. In consideration of the importance of nitrogen containing heterocyclic compounds in organic and pharmaceutical chemistry, developing a new aza-Nazarov reaction will have the potential to be beneficial in many synthetic applications. In this work, a novel catalytic aza-Nazarov reaction between 3,4-dihydroisoquinolines and α,β-unsaturated acyl chlorides, that can be used for a broad range of substrates, has been developed. By taking advantage of the stabilizing β-silicon effect and the anion exchange strategy, the proposed reaction proceeds under much better conditions with respect to reaction yield, reaction conditions and environmental issues. Our initial efforts focused on the use of achiral anion exchange strategy employing silver trifluoromethanesulfonate (AgOTf) as the anion source to develop a novel aza-Nazarov reaction. To demonstrate that the reaction has a wide substrate scope, the substituents on the starting materials have been changed with electron withdrawing and donating groups. Several attempts have been made to render the developed reaction enantioselective using chiral catalysts, nevertheless asymmetric aza-Nazarov reactions could not be achieved. 171

A modular and waste‐free strategy for constructing N‐substituted cyclic amines via decarboxylative N‐alkylation of α‐amino acids employing ruthenium‐ and iron‐based catalysts is presented. The reported method allows the synthesis of a wide range of five‐ and six‐membered N‐alkylated heterocycles in moderate‐to‐excellent yields starting from predominantly proline and a broad range of benzyl alcohols, and primary and secondary aliphatic alcohols. Examples using pipecolic acid for the construction of piperidine derivatives, as well as the one‐pot synthesis of α‐amino nitriles, are also shown.

We thank the EPSRC Centre for Doctoral Training in Critical Resource Catalysis (CRITICAT, grant code EP/L016419/1, R.M.N.) for funding. We thank the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007–2013) ERC grant agreement no. 279850 (A.D.S.). A.D.S. thanks the Royal Society for a Wolfson Research Merit Award. We also thank the EPSRC UK National Mass Spectrometry Service at Swansea. The research data supporting this publication can be accessed at https://doi.org/10.17630/00aff760-0732-438f-a9d1-30c7cf3a87a0 A serendipitously-discovered process for the synthesis of heterocyclic products containing a novel fused indoline-cyclobutanone ring system is reported. This process is believed to take place through in situ generation of a ketene intermediate, followed by intramolecular [2+2] cycloaddition with a pendant enamide. The formation of a ketene intermediate in this process is significant as the reaction conditions employed are analogous to those commonly used in tertiary amine Lewis base catalysis, where the potential intermediacy of ketenes is an important consideration that is often overlooked. Postprint

Aza-Heck cyclizations initiated by oxidative addition of Pd0-catalysts into the N−O bond of N-(pentafluoro-benzoyloxy)sulfonamides are described. These studies, which encompass only the second class of aza-Heck reaction developed to date, provide direct access to diverse N-heterocyclic ring systems.

The design of multistrain systems has markedly expanded the prospects of using long biosynthetic pathways to produce natural compounds. However, the cooperative use of artificially engineered microbes to synthesize xenobiotic chemicals from renewable carbohydrates is still in its infancy. Here, a microbial system is developed for the production of high‐added‐value N‐heterocycles directly from glucose. Based on a retrosynthetic analysis, eleven genes are selected, systematically modulated, and overexpressed in three Escherichia coli strains to construct an artificial pathway to produce 5‐methyl‐2‐pyrazinecarboxylic acid, a key intermediate in the production of the important pharmaceuticals Glipizide and Acipimox. Via one‐pot tandem collaborations, the designed microbes remarkably realize high‐level production of 5‐methyl‐2‐pyrazinecarboxylic acid (6.2 ± 0.1 g L−1) and its precursor 2,5‐dimethylpyrazine (7.9 ± 0.7 g L−1). This study is the first application of cooperative microbes for the total biosynthesis of functionalized N‐heterocycles and provides new insight into integrating bioretrosynthetic principles with synthetic biology to perform complex syntheses., A microbial system with three engineered Escherichia coli strains is developed for the production of N‐heterocycles directly from glucose. Via one‐pot tandem collaborations, it realizes high‐level production of 5‐methyl‐2‐pyrazinecarboxylic acid, a key intermediate for the important pharmaceuticals Glipizide and Acipimox. This work provides new insight into integrating bioretrosynthetic principles with synthetic biology to perform complex syntheses.

Saturated nitrogen heterocycles can be found with increasing abundance in bioactive molecules despite a limited number of methods to access these scaffolds. However, the coupling of recently introduced SnAP [tin (Sn) amine protocol] reagents with a wide range of aldehydes and ketones has proven to be a reliable, practical, and versatile one-step approach to saturated N-heterocycles. While effective, the lack of mechanistic understanding limits efforts to develop new catalytic and enantioselective variants. To distinguish between a polar or radical mechanism, we assessed Lewis and Brønsted acids, radical trapping experiments, and radical clock SnAP reagents reinforcing the current understanding of the SnAP protocol as a radical cyclization., Synlett, 30 (4), ISSN:1437-2096, ISSN:0936-5214