AgNTf₂-catalyzed formal [3 + 2] cycloaddition of ynamides with unprotected isoxazol-5-amines: efficient access to functionalized 5-amino-1H-pyrrole-3-carboxamide derivatives

• Ziping Cao,
• Jiekun Zhu,
• Li Liu,
• Yuanling Pang,
• Laijin Tian,
• Xuejun Sun and
• Xin Meng

Beilstein J. Org. Chem. 2019, 15, 2623–2630, doi:10.3762/bjoc.15.255

• employment of isoxazole nucleophiles in gold-catalyzed formal [3 + 2] cycloaddition reaction of ynamides [31][32], and zinc-catalyzed the reaction of ynol ethers [33], giving the respective multi-substituted pyrrole derivatives efficiently (Scheme 2a) [34][35]. The reaction proceeds via an α-imino gold

Effect of ring size on photoisomerization properties of stiff stilbene macrocycles

• Sandra Olsson,
• Óscar Benito Pérez,
• Magnus Blom and
• Adolf Gogoll

Beilstein J. Org. Chem. 2019, 15, 2408–2418, doi:10.3762/bjoc.15.233

• ]+ calcd for C30H38O4, 463; found, 463; HRMS (CI) m/z: [M + H]+ calcd for C30H38O4, 463.2843; found, 463.2836; UV–vis (CH2Cl2) λmax: 320, 248 nm. General procedure B: McMurry coupling Zinc powder previously grinded (12 equiv) was suspended in dry THF (30 mL). The suspension was cooled to 0 °C in an ice

Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups

• Xiaowei Li,
• Xiaolin Shi,
• Xiangqian Li and
• Dayong Shi

Beilstein J. Org. Chem. 2019, 15, 2213–2270, doi:10.3762/bjoc.15.218

• for the difluoromethylation of aryl-substituted acrylic acids was also achieved by Liu and co-workers. The HCF2-substituted E-alkenes were finally obtained with iron catalysis and zinc difluoromethanesulfinate ((CF2HSO2)2Zn, Baran reagent). Also, the authors proved that the formation of the Cvinyl–CF3

1,2,3-Triazolium macrocycles in supramolecular chemistry

• Mastaneh Safarnejad Shad,
• Pulikkal Veettil Santhini and
• Wim Dehaen

Beilstein J. Org. Chem. 2019, 15, 2142–2155, doi:10.3762/bjoc.15.211

• synthesized the novel tetra-1,2,3-triazolium zinc porphyrin cage 3 (Figure 4) and have probed its characteristics by using UV–visible spectroscopy, determining the association constants for complex formation in 5% water/acetone. This receptor has shown affinity toward all of the halide ions and especially

• triazole containing dialdehyde and binaphthyl with dipyrromethene, followed by zinc metalation and subsequent reaction with MeI resulted in the synthesis of the two-component catalytic system 16 (Figure 13). Here, the cooperative effect of nucleophilic triazolium moieties, their counter ion near the

Design, synthesis and biological evaluation of immunostimulating mannosylated desmuramyl peptides

• Rosana Ribić,
• Ranko Stojković,
• Lidija Milković,
• Mariastefania Antica,
• Marko Cigler and
• Srđanka Tomić

Beilstein J. Org. Chem. 2019, 15, 1805–1814, doi:10.3762/bjoc.15.174

• peracetylated mannose 8 was performed using the mild acidic catalyst, zinc acetate hydrate [33]. The reaction progress was monitored by thin-layer chromatography. Within the first 20 hours compound 9 was the only product and further progress resulted in gradual removal of the remaining acetate groups. The SN2

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

• activity. It is revealed from the literature that next to the copper, palladium catalysts in the form of salts (with or without ligands), complexes, NPs, etc. find their usage on mass scale syntheses of IPs. The role of zinc in synthetic chemistry Zinc salts being inexpensive, environmentally benign, low

• in toxicity and fits to the tenets of green chemistry. Zinc in the form of its salts, complexes (chelated by mono/di/tri/tetradentate ligands), oxides and sulfides proved to be a promising and active catalyst for organic chemists in both homogeneous as well as heterogeneous reaction systems [23][59

• systems based on zinc with excellent activity has been designed and used. The role of iron in synthetic chemistry Iron being the most abundant heavy element on earth with low biological toxicity along with cost economy and high reactivity was explored by Kharasch and Fields in the 1940s and Tamura and

Borylation and rearrangement of alkynyloxiranes: a stereospecific route to substituted α-enynes

• Ruben Pomar Fuentespina,
• José Angel Garcia de la Cruz,
• Gabriel Durin,
• Victor Mamane,
• Jean-Marc Weibel and
• Patrick Pale

Beilstein J. Org. Chem. 2019, 15, 1416–1424, doi:10.3762/bjoc.15.141

• ]. Alternatively, Unemaya et al. and more recently Buchwald et al. described a Negishi cross coupling of aryl bromides or chlorides to α-CF3-oxiranyl zincates generated by lithiation of trifluoromethyloxirane and transmetalation with zinc chloride [10][11]. In this context and based on the pioneering work of

Selenophene-containing heterotriacenes by a C–Se coupling/cyclization reaction

• Pierre-Olivier Schwartz,
• Sebastian Förtsch,
• Astrid Vogt,
• Elena Mena-Osteritz and
• Peter Bäuerle

Beilstein J. Org. Chem. 2019, 15, 1379–1393, doi:10.3762/bjoc.15.138

• B3LYP and CAMB3LYP functional and 6-31++(d,p) basis-set [56]. Materials Iodine, zinc(II) chloride, copper(II) chloride, potassium hydroxide, chlorotrimethylsilane, copper(I) iodide, and potassium phosphate were purchased from Merck. Diisopropylamine, bis(dibenzylideneacetone)palladium(0

• was stirred at −78 °C for 1.5 hours after complete addition of LDA and then a solution of zinc(II) chloride (1.0 g, 7.3 mmol) dissolved in 5.6 mL dry THF was added. After stirring for one hour at 0 °C, copper(II) chloride (986 mg, 7.3 mmol) was added in one portion and the resulting mixture was

Selective detection of DABCO using a supramolecular interconversion as fluorescence reporter

• Indrajit Paul,
• Debabrata Samanta,
• Sudhakar Gaikwad and
• Michael Schmittel

Beilstein J. Org. Chem. 2019, 15, 1371–1378, doi:10.3762/bjoc.15.137

• -component rectangle [Cu4(1)2(2)2]4+ and the four-component sandwich complex [Cu2(1)(2)(4)]2+ is triggered by inclusion and release of DABCO (4). The fully reversible and clean switching between two multicomponent supramolecular architectures can be monitored by fluorescence changes at the zinc porphyrin

• sites. The structural changes are accompanied by a huge spatial contraction/expansion of the zinc porphyrin–zinc porphyrin distances that change from 31.2/38.8 Å to 6.6 Å and back. The supramolecular interconversion was used for the highly selective detection of DABCO in a mixture of other similar

• compounds. Keywords: copper; detection; fluorescence; interconversion; macrocycles; self-assembly; self-sorting; zinc porphyrin; Introduction Since dynamic multicomponent supramolecular structures are nowadays abundant [1][2], the weak intercomponent binding [3][4][5][6][7][8][9] is often instrumentalized

One-pot activation–alkynylation–cyclization synthesis of 1,5-diacyl-5-hydroxypyrazolines in a consecutive three-component fashion

• Christina Görgen,
• Katharina Boden,
• Guido J. Reiss,
• Walter Frank and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2019, 15, 1360–1370, doi:10.3762/bjoc.15.136

• (Figure 2) [26][27]. In addition, 1-acyl-5-hydroxypyrazolines are bidentate ligands for zinc complexes and by virtue of being ring tautomers of β-enolhydrazones they can also act as tridentate ligands for nickel [28] and tin [29][30] complexes. In contrast, dimethylzinc forms dimeric complexes where the 1

Synthesis of dipolar molecular rotors as linkers for metal-organic frameworks

• Sebastian Hamer,
• Fynn Röhricht,
• Marius Jakoby,
• Ian A. Howard,
• Xianghui Zhang,
• Christian Näther and
• Rainer Herges

Beilstein J. Org. Chem. 2019, 15, 1331–1338, doi:10.3762/bjoc.15.132

• higher yields. Starting from commercially available 5,6-dibromo-1,3-benzodioxole (13a) and literature known 6,7-dibromo-1,4-benzodioxane (13b) [55], dicyanation of the dibromo compounds was achieved with zinc(II) cyanide under palladium catalysis [56]. The typical Rosemund–von-Braun reaction using copper

Synthesis of aryl cyclopropyl sulfides through copper-promoted S-cyclopropylation of thiophenols using cyclopropylboronic acid

• Emeline Benoit,
• Ahmed Fnaiche and
• Alexandre Gagnon

Beilstein J. Org. Chem. 2019, 15, 1162–1171, doi:10.3762/bjoc.15.113

• with hydrobromic acid and zinc bromide leads to 1-arylthiocyclobutenes 7 [13] and 2-alkyl-substituted cyclobutanones 8 [11][12], respectively. Treatment of 6 with hydrobromic acid and zinc bromide in the presence of a thiophenol provides the 1,1-di(arylthio)cyclobutane 9 which, upon reaction with

Multicomponent reactions (MCRs): a useful access to the synthesis of benzo-fused γ-lactams

• Edorta Martínez de Marigorta,
• Jesús M. de Los Santos,
• Ana M. Ochoa de Retana,
• Javier Vicario and
• Francisco Palacios

Beilstein J. Org. Chem. 2019, 15, 1065–1085, doi:10.3762/bjoc.15.104

• procedure has been described by Singh and co-workers [85], who used formylbenzoate 29 and preformed enol ethers instead of ketones in a Mukaiyama–Mannich lactamization reaction catalysed by zinc or copper under mild conditions. A large amount of diverse isoindolinones 32 (thirty-four examples) can be built

• yields (22 examples, 82–97% yields) [94]. On the contrary, another Strecker multicomponent synthesis, between 2-formylbenzoate 29, benzylamine and potassium cyanide, carried out under mechanochemical conditions and zinc catalysis, only produced a 31% yield of the corresponding cyanoisoindolinone 53a (R1

Coordination chemistry and photoswitching of dinuclear macrocyclic cadmium-, nickel-, and zinc complexes containing azobenzene carboxylato co-ligands

• Jennifer Klose,
• Tobias Severin,
• Peter Hahn,
• Alexander Jeremies,
• Jens Bergmann,
• Daniel Fuhrmann,
• Jan Griebel,
• Bernd Abel and
• Berthold Kersting

Beilstein J. Org. Chem. 2019, 15, 840–851, doi:10.3762/bjoc.15.81

• with λ = 365 nm reveals a photoisomerization of the co-ligand from the trans to the cis form. Keywords: azobenzene carboxylates; cadmium; complexes; macrocyclic ligands; nickel; zinc; Introduction The macrocyclic N6S2 donor ligand H2L is an effective dinucleating ligand that supports a large number

• , SQUID magnetometry and X-ray crystallography is reported herein. Preliminary results concerning the photoisomerization of compound 1 are reported as well. Results and Discussion Synthesis of ligands and metal complexes Scheme 1 shows the synthetic procedures. The yellow-orange colored zinc complexes (3

• determine their structures in solution the diamagnetic zinc and cadmium complexes were subjected to 1H and 13C NMR spectroscopic studies. Table 2, and Tables S4 and S5 (Supporting Information File 1) list the 1H and 13C NMR spectroscopic data for complexes 1, 3, 5, 6 and 8. The data for [Zn2L(μ-OAc)]+ and

Design, synthesis and spectroscopic properties of crown ether-capped dibenzotetraaza[14]annulenes

• Krzysztof M. Zwoliński and
• Julita Eilmes

Beilstein J. Org. Chem. 2019, 15, 617–622, doi:10.3762/bjoc.15.57

• differentiated Lewis-basic binding sites, however, from a broader perspective, the nature of the DBTAA binding site can be easily switched into a Lewis-acidic one after appropriate metal insertion (e.g., with zinc(II) ions) [33]. The crown-capped DBTAA’s were synthesized by refluxing 1,4,10-trioxa-7,13

Synthesis of the polyketide section of seragamide A and related cyclodepsipeptides via Negishi cross coupling

• Jan Hendrik Lang and
• Thomas Lindel

Beilstein J. Org. Chem. 2019, 15, 577–583, doi:10.3762/bjoc.15.53

• , geodiamolides and seragamides, is reported. The key step is a Negishi cross coupling of (R)-(3-methoxy-2-methyl-3-oxopropyl)zinc(II) bromide and an (E)-iodoalkene that was synthesized via an aluminium ester enolate attack at (R)-propylene oxide. The overall synthesis comprises nine steps with an overall yield

• ), MeI (4-Me), and (R)-(3-methoxy-2-methyl-3-oxopropyl)zinc(II) bromide (8, C1–C3, 2-Me). We obtained 8-hydroxyester 7 within nine steps and an overall yield of 21% starting from (R)-propylene oxide. The efficiency of our route to polyketide 7 compares well to earlier approaches. It proved to be possible

Study on the regioselectivity of the N-ethylation reaction of N-benzyl-4-oxo-1,4-dihydroquinoline-3-carboxamide

• Pedro N. Batalha,
• Luana da S. M. Forezi,
• Maria Clara R. Freitas,
• Nathalia M. de C. Tolentino,
• Ednilsom Orestes,
• José Walkimar de M. Carneiro,
• Fernanda da C. S. Boechat and
• Maria Cecília B. V. de Souza

Beilstein J. Org. Chem. 2019, 15, 388–400, doi:10.3762/bjoc.15.35

• carboxamide group, may contribute to enhance the bioactivity. This fact could be explained by the coplanarity induced by the C-4 carbonyl hydrogen bond interactions with biological targets [3] or complexation with physiological metal cations such as magnesium and zinc [23]. Besides the derivatives 3a and 3b

Synthesis of C₃-symmetric star-shaped molecules containing α-amino acids and dipeptides via Negishi coupling as a key step

• Sambasivarao Kotha and
• Saidulu Todeti

Beilstein J. Org. Chem. 2019, 15, 371–377, doi:10.3762/bjoc.15.33

• . Results and Discussion The required zinc insertion compound 7 was prepared from L-serine (3). Thus, commercially available L-serine (3) was treated with acetyl chloride in methanol to give methyl ester 4, which was subjected to N-Boc protection with di-tert-butyl dicarbonate (Boc2O) and triethylamine in

• iodo compound 6 was treated with freshly activated Zn in DMF at room temperature to afford the zinc insertion product 7 (Scheme 1) [43]. With the organozinc compound 7 at hand we turned to the synthesis of the halide component for the attempted Negishi coupling. For this 4-iodoacetophenone (8) was

• resonance (13C NMR, 100 MHz and 125 MHz) spectra were recorded on a Bruker spectrometer. The high-resolution mass measurements were carried out by using electrospray ionization (ESI) spectrometer. Melting points were recorded on a Veego melting point apparatus. Negishi coupling product 10 Zinc (Zn) dust was

Synthesis of 1,2-divinylcyclopropanes by metal-catalyzed cyclopropanation of 1,3-dienes with cyclopropenes as vinyl carbene precursors

• Jesús González,
• Alba de la Fuente,
• María J. González,
• Laura Díez de Tejada,
• Luis A. López and
• Rubén Vicente

Beilstein J. Org. Chem. 2019, 15, 285–290, doi:10.3762/bjoc.15.25

• generate the corresponding zinc–vinyl carbene to efficiently prepare vinylcyclopropane derivatives with a remarkable broad scope (Scheme 1c) [26]. In view of these precedents, we decided to study the feasibility of this reaction in the synthesis of 1,2-divinylcyclopropanes by using 1,3-dienes as trapping

• equimolar mixture of cis/trans diastereoisomers (cis refers to both vinyl substituents). Even though the lack of selectivity was already noticed by Uemura and co-workers in related reactions [17], we attempted the reaction with other zinc salts or rhodium(II) carboxylates as catalysts. Unfortunately, these

• as catalyst allowed the isolation of diastereomerically pure endo-7a,b oxabicycles showing the 1,2-divinylcyclopropane moiety. In contrast, [Rh2(OAc)4] afforded complex reaction mixtures. In spite of the modest yields, this zinc-catalyzed reaction deserves some comments as it constitutes a rare

Olefin metathesis in multiblock copolymer synthesis

• Maria L. Gringolts,
• Yulia I. Denisova,
• Eugene Sh. Finkelshtein and
• Yaroslav V. Kudryavtsev

Beilstein J. Org. Chem. 2019, 15, 218–235, doi:10.3762/bjoc.15.21

• (cyclohexene carbonate)s was carried out by the β-diiminate (BDI) zinc-catalyzed block copolymerization of functionalized epoxides and CO2 with a norbornenyl-containing initiator (Scheme 5) [68]. The subsequent “grafting through” by ROMP of norbornene resulted in the synthesis of multiblock copolymer brushes

Protein–protein interactions in bacteria: a promising and challenging avenue towards the discovery of new antibiotics

• Laura Carro

Beilstein J. Org. Chem. 2018, 14, 2881–2896, doi:10.3762/bjoc.14.267

• optimization due to its physicochemical properties and its potential for fragment growth. After virtual screening and binding studies by STD-NMR studies, the authors were able to find tetrazole 32 (Figure 7) which had a three-fold improved affinity (Kd = 1.3 mM) compared to the initial hit 31. Later, the ZINC

Unnatural α-amino ethyl esters from diethyl malonate or ethyl β-bromo-α-hydroxyiminocarboxylate

• Eloi P. Coutant,
• Vincent Hervin,
• Glwadys Gagnot,
• Candice Ford,
• Racha Baatallah and
• Yves L. Janin

Beilstein J. Org. Chem. 2018, 14, 2853–2860, doi:10.3762/bjoc.14.264

• for the low yield observed and could be sometimes acted upon. In any case, the final reduction of the α-hydroxyimino esters 2b–al using zinc and hydrochloric acid in ethanol gave the α-amino esters 1b–al, which were usually of a high purity grade without recourse to a chromatography. In few cases

• , 27 and 32 in 31–88% overall yield. These were then reduced into the corresponding α-amino esters 22, 24, 26, 28 and 33 using zinc and hydrochloric acid. We also focused on the preparation of the β-methylated furan-bearing α-hydroxyimino ester 35. The introduction of the methyl group was achieved

• (hydrochloric and powdered zinc) and we successfully used instead the much milder [34] mixture of ammonium formate and zinc in ethanol at room temperature to give 43% of the target α-amino ester 53. The same strategy gave the corresponding α-amino ester homolog 58 from the readily available dioxane derivative

Synthesis of unnatural α-amino esters using ethyl nitroacetate and condensation or cycloaddition reactions

• Glwadys Gagnot,
• Vincent Hervin,
• Eloi P. Coutant,
• Sarah Desmons,
• Racha Baatallah,
• Victor Monnot and
• Yves L. Janin

Beilstein J. Org. Chem. 2018, 14, 2846–2852, doi:10.3762/bjoc.14.263

• esters. This started with a study of its condensation with various arylacetals to give ethyl 3-aryl-2-nitroacrylates followed by a reduction (NaBH4 and then zinc/HCl) into α-amino esters. The scope of this method was explored as well as an alternative with arylacylals instead. We also focused on various

• significantly improved 46% yield of 6r, in comparison with our single trial via 5r, which ended up with less than 20% of an impure sample of 6r. Finally, from the isolated α-nitro esters 6a–s, their reduction into the corresponding α-amino esters 1a–s, using zinc and hydrochloric acid in ethanol usually

• proceeded in good yield, although care had to be taken during work-up as zinc complexes required the addition of an excess of ammonia to fully break in the course of the extraction. In an attempt to overcome the lack of condensation between ethyl nitroacetate (4) and electron-poor substrates 5j–l, we

Synthesis of mono-functionalized S-diazocines via intramolecular Baeyer–Mills reactions

• Miriam Schehr,
• Daniel Hugenbusch,
• Tobias Moje,
• Christian Näther and
• Rainer Herges

Beilstein J. Org. Chem. 2018, 14, 2799–2804, doi:10.3762/bjoc.14.257

• benzyl bromides 8–11, which were commercially available or synthesized by radical bromination. The S-diazocines precursors 13–16 were then subjected to the intramolecular Baeyer–Mills reaction yielding the S-diazocines 1–4. In the first step the nitro group was reduced with zinc powder to the

• zinc and the oxidation from the hydroxylamine to the nitroso compound. These reaction steps are difficult to monitor and furthermore the S-diazocine yield depends on the nature of substituents. However, the overall yields and the reliability of the formation of the azo group are superior to previously

• conditions: i) MeCN, AIBN, NBS; ii) NaBH4, THF; #commercially available iii) BH3·THF complex, THF, *product 17 is not stable; iv) 1. Zinc powder, ammonium chloride, ethanol, 2. Fe(III)Cl3 hexahydrate, H2O/ethanol, acetic acid. Comparison of previous diazocine syntheses approaches compared to the present

Copolymerization of epoxides with cyclic anhydrides catalyzed by dinuclear cobalt complexes

• Yo Hiranoi and
• Koji Nakano

Beilstein J. Org. Chem. 2018, 14, 2779–2788, doi:10.3762/bjoc.14.255

• epoxide/CA copolymerization was constricted until recently because of low catalytic activity and poor control over the main chain sequence (formation of ether linkages through consecutive epoxide enchainment) and molecular weight. In 2007, Coates and co-workers reported that β-diiminate zinc complexes