Facile synthesis of 7-alkyl-1,2,3,4-tetrahydro-1,8-naphthyridines as arginine mimetics using a Horner–Wadsworth–Emmons-based approach

• Rhys A. Lippa,
• John A. Murphy and
• Tim N. Barrett

Beilstein J. Org. Chem. 2020, 16, 1617–1626, doi:10.3762/bjoc.16.134

• to account for the deprotonation of the more acidic phosphonate product 7 versus the starting material 13, and potential lithium sequestration by chelation between an oxygen atom of the phosphonate and the nitrogen atom of the unsaturated ring. Monitoring of the deprotonation followed by quenching

4-Hydroxy-3-methyl-2(1H)-quinolone, originally discovered from a Brassicaceae plant, produced by a soil bacterium of the genus Burkholderia sp.: determination of a preferred tautomer and antioxidant activity

• Dandan Li,
• Naoya Oku,
• Yukiko Shinozaki,
• Yoichi Kurokawa and
• Yasuhiro Igarashi

Beilstein J. Org. Chem. 2020, 16, 1489–1494, doi:10.3762/bjoc.16.124

• Azurol S-Fe3+ (CAS) [45], which required a 1600 times higher concentration for metal-chelation. Thus, compound 1 was found to be another example of the antioxidant from Burkholderia. Detailed studies on the antioxidation mechanism of 1 is now underway. Experimental General experimental procedures UV and

Synthesis, antiinflammatory activity, and molecular docking studies of bisphosphonic esters as potential MMP-8 and MMP-9 inhibitors

• Abimelek Cortes-Pacheco,
• María Adelina Jiménez-Arellanes,
• Francisco José Palacios-Can,
• José Antonio Valcarcel-Gamiño,
• Rodrigo Said Razo-Hernández,
• María del Carmen Juárez-Vázquez,
• Adolfo López-Torres and
• Oscar Abelardo Ramírez-Marroquín

Beilstein J. Org. Chem. 2020, 16, 1277–1287, doi:10.3762/bjoc.16.108

• expected, 4–6 could bind the Zn2+ ion in a monodentate fashion through the oxygen atom double bonded to the phosphorus atom (P=O) of one of the phosphonate moieties, as reported in the literature for other structures [38][39]. Only for 3, zinc chelation was observed through the oxygen atom double bonded to

• the carbon atom (C=O) of the ester group (Figure 3). In all cases, a distorted tetrahedral coordination geometry was observed for the zinc ion, caused by the chelation with His197, Glu198, and His207 residues. His201 was far apart from the catalytic site, and the basic nitrogen atom in this residue

• was pointing away from the zinc ion [39]. The calculated distances from the Zn2+ ion and the different sites at the ligand and the protein are summarized in Table 5. The zinc chelation in MMP-9 occurred in a different way. The predicted orientation of the histidine residues at the catalytic site were

Recent developments in photoredox-catalyzed remote ortho and para C–H bond functionalizations

• Rafia Siddiqui and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 248–280, doi:10.3762/bjoc.16.26

• various functional groups (Scheme 8). The detailed proposed mechanism for the constructions of these intriguing molecules is shown in Figure 11. C–H benzoyloxylation: monobenzoyloxylation without chelation assistance Inspired by the innovative work reported by Tokumaru [112] and MacMillan [113], Li’s

• thiolation. Synthesis of indoles via C–H cyclization of anilides with alkynes. Preparation of 3-trifluoromethylcoumarins via C–H cyclization of arylpropiolate esters. Monobenzoyloxylation without chelation assistance. Aryl-substituted arenes prepared by inorganic photoredox catalysis using 12a. Arylation of

Synthesis and herbicidal activities of aryloxyacetic acid derivatives as HPPD inhibitors

• Man-Man Wang,
• Hao Huang,
• Lei Shu,
• Jian-Min Liu,
• Jian-Qiu Zhang,
• Yi-Le Yan and
• Da-Yong Zhang

Beilstein J. Org. Chem. 2020, 16, 233–247, doi:10.3762/bjoc.16.25

• -dicarbonyl bidentate chelation with the active center metal, and 2) through favorable sandwich π–π stacking interactions between aromatic rings and the Phe360, Phe403 residues of the active site. Thus, 1,3-dicarbonyl and aromatic moieties are indispensable pharmacophores for potent HPPD-inhibiting compounds

Why do thioureas and squaramides slow down the Ireland–Claisen rearrangement?

• Dominika Krištofíková,
• Juraj Filo,
• Mária Mečiarová and
• Radovan Šebesta

Beilstein J. Org. Chem. 2019, 15, 2948–2957, doi:10.3762/bjoc.15.290

• solvent and the amine’s structure [22][23]. The decomposition of the enolate is one of the side reactions, which can be suppressed by chelation. The chelation-stabilized enolates are more stable than the corresponding silyl ketene acetals, and they are capable of a direct rearrangement [24]. The chelation

Photoreversible stretching of a BAPTA chelator marshalling Ca²⁺-binding in aqueous media

• Aurélien Ducrot,
• Arnaud Tron,
• Robin Bofinger,
• Ingrid Sanz Beguer,
• Jean-Luc Pozzo and
• Nathan D. McClenaghan

Beilstein J. Org. Chem. 2019, 15, 2801–2811, doi:10.3762/bjoc.15.273

• differences between them, which may have consequences on the chelation, energy-minimized (PM6) structures were determined (Figure 2). The trans-form was found to be the lowest energy structure, as is generally observed for azobenzenes [37]. In the trans- versus cis-chelates the following bond lengths were

Combining the Ugi-azide multicomponent reaction and rhodium(III)-catalyzed annulation for the synthesis of tetrazole-isoquinolone/pyridone hybrids

• Gerardo M. Ojeda,
• Prabhat Ranjan,
• Pavel Fedoseev,
• Lisandra Amable,
• Upendra K. Sharma,
• Daniel G. Rivera and
• Erik V. Van der Eycken

Beilstein J. Org. Chem. 2019, 15, 2447–2457, doi:10.3762/bjoc.15.237

• in the literature supporting the chelation of metal centers by a tetrazole ring during the C–H activation processes, in which the tetrazole may also act as directing group [55][56][57][58][59][60][61]. The closely related triazole ring has also been used for the C–H modification of amino acids and

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

• the corresponding products with wide substrate tolerance in moderate to good yields (Scheme 82). After one year, the group of Cai [147] presented a Cu(II)-catalyzed 8-amido chelation-induced regioselective C5-trifluoromethylation of quinolines (Scheme 83a). With CuBr2 as a catalyst and

N-(1-Phenylethyl)aziridine-2-carboxylate esters in the synthesis of biologically relevant compounds

• Iwona E. Głowacka,
• Aleksandra Trocha,
• Andrzej E. Wróblewski and
• Dorota G. Piotrowska

Beilstein J. Org. Chem. 2019, 15, 1722–1757, doi:10.3762/bjoc.15.168

• NaBH4/ZnCl2 mixture (chelation controlled) gave the aziridine alcohol 20 as a major product. Reductive opening of the aziridine ring produced the amino alcohol 21 which was transformed into the substituted oxazolidin-2-one 22. Its catalytic hydrogenation effected deoxygenation at the benzylic position

• assured when a NaBH4/ZnCl2 mixture was applied in a chelation-controlled reduction of the ketone (2S,1'R)-93 to provide the (R)-alcohol (2S,1'R,1''R)-94 as a major (94:6) product. Alcohols (2S,1'S,1''R)- and (2S,1'R,1''R)-94 were transformed into N-Boc-safingol (2S,3S)-95 and N-Boc-ᴅ-erythro-sphinganine

• )-184 and its C4 epimer (2S,3R,4S,5R)-184 were accomplished from the aziridine aldehyde (2R,1'S)-6 (Scheme 49) [105]. The Lewis acid-catalyzed nucleophilic anti-addition of 2-trimethylsilyloxyfuran to (2R,1'S)-6 furnished diastereoisomerically pure secondary alcohol 185 since chelation-controlled

Introduction of an isoxazoline unit to the β-position of porphyrin via regioselective 1,3-dipolar cycloaddition reaction

• Xiujun Liu,
• Xiang Ma and
• Yaqing Feng

Beilstein J. Org. Chem. 2019, 15, 1434–1440, doi:10.3762/bjoc.15.143

• enantiomers of 3a is present, which assembled to a dimeric structure with the fifth chelation of a Zn2+ ion by the carbonyl group of the other molecule. The self-dimerization property of 3a may be utilized in supramolecular chemistry [50][51][52][53]. Experimental 1: Porphyrin phosphonium salt 1 was prepared

Synthesis of the aglycon of scorzodihydrostilbenes B and D

• Katja Weimann and
• Manfred Braun

Beilstein J. Org. Chem. 2019, 15, 610–616, doi:10.3762/bjoc.15.56

• transition metal-mediated, regioselective, chelation-directed activation of an aryl–hydrogen bond. A promising approach was seen in an application of Murai’s elegant ruthenium-catalyzed ortho-functionalization of aryl alkyl ketones and their addition to olefins [11][12][13][14][15]. This route appeared

• -D-glucose pentaacetate in the presence of an excess of boron trifluoride etherate [20], a regioselective reaction occurred at the phenolic group in ortho-position to the alkyl side chain to give mono-glycosylated product 12. Chelation of the carbonyl and the neighboring phenolic group by the Lewis

Synthesis of nonracemic hydroxyglutamic acids

• Dorota G. Piotrowska,
• Iwona E. Głowacka,
• Andrzej E. Wróblewski and
• Liwia Lubowiecka

Beilstein J. Org. Chem. 2019, 15, 236–255, doi:10.3762/bjoc.15.22

• stereoselectivity of the cyclocondensation step is best explained by the attack on a re-face of the C=O group due to chelation of Zn2+ to the carbonyl oxygen and amide nitrogen/oxygen atoms [49]. A better approach in terms of carbon atom economy relied on the addition of allylmagnesium chloride to the aldehyde (R

• subjected to Reformatsky reaction to give a 92:8 mixture of (2S,3R)-11 and (2S,3S)-11, respectively. The major diastereoisomer was formed by the attack on the re-face of the carbonyl group in accordance with the non-chelation Felkin–Ahn model 12 in which the largest substituent at Cα (orthoester) is

Catalysis of linear alkene metathesis by Grubbs-type ruthenium alkylidene complexes containing hemilabile α,α-diphenyl-(monosubstituted-pyridin-2-yl)methanolato ligands

• Tegene T. Tole,
• Johan H. L. Jordaan and
• Hermanus C. M. Vosloo

Beilstein J. Org. Chem. 2019, 15, 194–209, doi:10.3762/bjoc.15.19

• ligand, and that was to focus on substituents on the α-carbon of the ligand. To our knowledge, there are no reports on investigations of electronic and/or steric effect(s) of pyridinyl substituents on the chelation efficiency of pyridinyl alcoholato ligands, and subsequently its metathesis activity

• chelation. The activity of the precatalysts also showed a significant improvement upon increasing the reaction temperature from 40 to 110 °C. The increase in the activity of the precatalysts is relatively low in the 40–60 °C range, but a high activity difference is observed upon increasing the temperature

• Ru–N bond (2.181 Å) in the geometry-optimised structure (Figure 9) of precatalyst 9 compared to that of the Ru–N bond (2.166 Å) of 6. A longer bond suggests a weaker Ru–N chelation thus a more active hemilabile complex. The difference in the Ru–N bond length may be attributed to the electron

Stereodivergent approach in the protected glycal synthesis of L-vancosamine, L-saccharosamine, L-daunosamine and L-ristosamine involving a ring-closing metathesis step

• Pierre-Antoine Nocquet,
• Aurélie Macé,
• Frédéric Legros,
• Jacques Lebreton,
• Gilles Dujardin,
• Sylvain Collet,
• Arnaud Martel,
• Bertrand Carboni and
• François Carreaux

Beilstein J. Org. Chem. 2018, 14, 2949–2955, doi:10.3762/bjoc.14.274

• was obtained in similar yield than one reported [8][47]. Synthesis of daunosamine and ristosamine glycals. As previously, the chiral pool material 5 was used for this unbranched glycal synthesis (Scheme 4). The first step was the chelation-controlled addition of allylmagnesium bromide to 5 to provide

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

• the stronger lithium diisopropylamide. We do not have an explanation for this observation, although such oximation was achieved (in a low yield) when starting from the phenyl-bearing analogue 36 as described below. We suggest a somehow forbidding cation chelation by the oxygen of the furan ring which

Ring-opening metathesis of some strained bicyclic systems; stereocontrolled access to diolefinated saturated heterocycles with multiple stereogenic centers

• Zsanett Benke,
• Melinda Nonn,
• Márton Kardos,
• Santos Fustero and
• Loránd Kiss

Beilstein J. Org. Chem. 2018, 14, 2698–2707, doi:10.3762/bjoc.14.247

• of the behavior of the catalyst efficiency is a rather difficult task. Metathesis reactions are known to be often catalyst or substrate dependent. Electronic or steric factors, and chelation effects may contribute to the outcome of metathesis in view of the yield. Moreover, possible H-bonding

Cobalt- and rhodium-catalyzed carboxylation using carbon dioxide as the C1 source

• Tetsuaki Fujihara and
• Yasushi Tsuji

Beilstein J. Org. Chem. 2018, 14, 2435–2460, doi:10.3762/bjoc.14.221

• occur at the relatively acidic C–H bond. Regarding Rh as the catalyst, Iwasawa et al. first reported a rhodium-catalyzed chelation-assisted C(sp2)–H carboxylation using methylaluminum as a reducing reagent (Scheme 27) [59]. Subsequently, the reaction of 2-phenylpyridine (29a) was performed using AlMe2

• reaction mechanism for this Rh-catalyzed chelation-assisted C(sp2)–H bond carboxylation is shown in Scheme 29. First, a low-valent methyl–Rh(I) species A is generated by transmetalation. Secondly, a pyridine ring in the substrate coordinates to the Rh center, which prompts the cleavage of the adjacent C–H

• Rh complex B (step a). Then, chelation-assisted C–H bond activation proceeds to generate a rhodacycle C (step b). The reaction of C with CO2 affords an eight-membered rhodacycle intermediate D (step c). Next, D is converted to the corresponding rhodium complex E by ligand exchange with KOAc (step d

Some mechanistic aspects regarding the Suzuki–Miyaura reaction between selected ortho-substituted phenylboronic acids and 3,4,5-tribromo-2,6-dimethylpyridine

• Piotr Pomarański,
• Piotr Roszkowski,
• Jan K. Maurin,
• Armand Budzianowski and
• Zbigniew Czarnocki

Beilstein J. Org. Chem. 2018, 14, 2384–2393, doi:10.3762/bjoc.14.214

• conclusions about the order of substitution. Also, the observed selectivity in the case of ortho-methoxyphenylboronic acid suggested an additional metal O-chelation effect in the transition state, apparently not present in the ortho-chloro analogues. The rotational barrier in selected atropisomers was

• transformation [22]. In such cases the stereoselectivity may depend on additional chelation effects [28][29][30][31][32][33][34]. Buchwald and co-workers reported an efficient stereoselective synthesis of axially chiral biarylamides by Pd–O bond formation during the oxidative addition step [28][29]. Also other

• research groups have shown beneficial impact of the additional palladium chelation on the products distribution [31][32][33][34]. We also observed an additional chelation effect (N-chelation) in the case of 4-amino-3,5-diaryl-2,6-dimethylpyridine derivatives [30]. The above mentioned examples illustrate

Hydroarylations by cobalt-catalyzed C–H activation

• Rajagopal Santhoshkumar and
• Chien-Hong Cheng

Beilstein J. Org. Chem. 2018, 14, 2266–2288, doi:10.3762/bjoc.14.202

• activation. In 1941, Kharasch and Fields applied a cobalt salt as the catalyst for the homocoupling of Grignard reagents [28]. After 15 years, Murahashi discovered a cobalt-catalyzed chelation-assisted ortho C–H carbonylation of azobenzene and imines as the preliminary example of directing group assisted C–H

β-Hydroxy sulfides and their syntheses

• Mokgethwa B. Marakalala,
• Edwin M. Mmutlane and
• Henok H. Kinfe

Beilstein J. Org. Chem. 2018, 14, 1668–1692, doi:10.3762/bjoc.14.143

• . Due to the absence of this kind of chelation effect, the copper(II) acetate fails to catalyze the addition of diphenyl disulfide to alkenes under the same reaction conditions. 3.3.2 Acetoxysulfenylation using copper iodide-bipyridine as a catalyst. Taniguchi reported a copper(II) iodide-catalyzed 1,2

Nanoreactors for green catalysis

• M. Teresa De Martino,
• Loai K. E. A. Abdelmohsen,
• Floris P. J. T. Rutjes and
• Jan C. M. van Hest

Beilstein J. Org. Chem. 2018, 14, 716–733, doi:10.3762/bjoc.14.61

• ]. This draw-back has been circumvented by using Pd-catalytic micelles, which were assembled in water using TMEDA (tetramethylethylenediamine) as additive. TMEDA was used to stabilize the Pd catalyst by chelation and indeed, presence of TMEDA resulted in higher yield [65]. High catalytic efficiency of

Carbohydrate inhibitors of cholera toxin

• Vajinder Kumar and
• W. Bruce Turnbull

Beilstein J. Org. Chem. 2018, 14, 484–498, doi:10.3762/bjoc.14.34

• inhibitors Hol and Fan [46] designed and synthesised both spanning and non-spanning bivalent inhibitors. “Spanning” means the ligand has sufficient length of the linker to reach the two binding moieties of CT, whereas “non-spanning” means there is insufficient linker length for intra-pentamer chelation, but

Fluorogenic PNA probes

• Tirayut Vilaivan

Beilstein J. Org. Chem. 2018, 14, 253–281, doi:10.3762/bjoc.14.17

• another strategy, the PNA may be terminally functionalized with chelating ligands, such as iminodiacetic acid, iminotriacetic acid or terminal dihistidine, to form the so-called Snap-to-it probes (Figure 7) [48]. The addition of divalent metal ions, such as Ni2+, results in an intramolecular chelation

• that contributes to the reduction in the background fluorescence of the single stranded (ss) probe by forcing the labels in close contact. In addition, the chelation also introduces an additional thermodynamic barrier into the binding of the DNA target to the unstructured PNA beacons that is akin to

Diastereoselective Mannich reactions of pseudo-C₂-symmetric glutarimide with activated imines

• Tatsuya Ishikawa,
• Tomoko Kawasaki-Takasuka,
• Toshio Kubota and
• Takashi Yamazaki

Beilstein J. Org. Chem. 2017, 13, 2473–2477, doi:10.3762/bjoc.13.244

• unambiguously determined by X-ray crystallographic analysis (Figure 1) [16]. Based on this information a possible reaction mechanism was formulated as depicted in Scheme 1. It is well-known that oxazolidinone-derived imides in general construct bidentate chelation when they are converted to the corresponding