Total syntheses of the archazolids: an emerging class of novel anticancer drugs

• Stephan Scheeff and
• Dirk Menche

Beilstein J. Org. Chem. 2017, 13, 1085–1098, doi:10.3762/bjoc.13.108

• alcohol 60. In this Δ5,6-trans-selective reaction the desired anti-diastereomer could be isolated in 85% with a dr of 6:1, which presumably arises from a chelation-controlled stereoselectivity [89]. The aldehyde 59 itself can be prepared in two steps from the corresponding Roche ester [90]. After

Synthesis of tetrasubstituted pyrazoles containing pyridinyl substituents

• Josef Jansa,
• Ramona Schmidt,
• Ashenafi Damtew Mamuye,
• Laura Castoldi,
• Alexander Roller,
• Vittorio Pace and
• Wolfgang Holzer

Beilstein J. Org. Chem. 2017, 13, 895–902, doi:10.3762/bjoc.13.90

• and not fully complete, also the subsequent reaction with CO2 was more sluggish in comparison to 3a,b what resulted in lower yields. The increased reactivity of 3a,b compared to 3c,d may be explained by the ability of the former to stabilize the intermediate organolithium species by chelation due to

A direct method for the N-tetraalkylation of azamacrocycles

• Andrew J. Counsell,
• Angus T. Jones,
• Matthew H. Todd and
• Peter J. Rutledge

Beilstein J. Org. Chem. 2016, 12, 2457–2461, doi:10.3762/bjoc.12.239

• ]. N-Tetraalkylation is a simple modification which can facilitate significant diversification of the macrocycle, often inducing marked changes to the chelation properties of the ligand [2][29]. From the first reports of N-tetramethylcyclam (1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) [29

Protonated paramagnetic redox forms of di-o-quinone bridged with p-phenylene-extended TTF: A EPR spectroscopy study

• Nikolay O. Chalkov,
• Vladimir K. Cherkasov,
• Gleb A. Abakumov,
• Andrey G. Starikov and
• Viacheslav A. Kuropatov

Beilstein J. Org. Chem. 2016, 12, 2450–2456, doi:10.3762/bjoc.12.238

• solution due to chelation. It should be mentioned, that the reduction of (1)H2 with copper metal proceeds also in the presence of non-bridging phosphines, such as PPh3, but the radical anion species (1·−)H2 is stable only in the presence of a large counterion such as [Cu(dppe)2]+. The signal of the solvent

Stereo- and regioselectivity of the hetero-Diels–Alder reaction of nitroso derivatives with conjugated dienes

• Lucie Brulíková,
• Aidan Harrison,
• Marvin J. Miller and
• Jan Hlaváč

Beilstein J. Org. Chem. 2016, 12, 1949–1980, doi:10.3762/bjoc.12.184

Synthesis and characterization of fluorinated azadipyrromethene complexes as acceptors for organic photovoltaics

• Forrest S. Etheridge,
• Roshan J. Fernando,
• Sandra Pejić,
• Matthias Zeller and
• Geneviève Sauvé

Beilstein J. Org. Chem. 2016, 12, 1925–1938, doi:10.3762/bjoc.12.182

• chelation [1][2][3][4]. BF2+-chelated ADP derivatives (Figure 1b) in particular have drawn interest for photodynamic therapy, bio-imaging and light harvesting applications [5][6][7][8]. We have shown that derivatives of Zn(ADP)2 are promising electron acceptors for organic photovoltaics (OPVs) [9][10]. A

• showed negligible power conversion efficiencies, and Zn(ADP)2 gave a maximum efficiency of 1.4% [11]. Free ligands and BF2+ chelates tend to self-aggregate too much, leading to large scale phase separation with P3HT and low PCEs. Chelation with zinc(II) lowers the tendency to self-aggregate, but Zn(ADP)2

• modifications allowed for the synthesis of all fluorinated WS3 derivatives in good yield with sufficient purity for chelation. The BF2+ chelation was carried out according to the literature procedures in moderate yields (Scheme 2) [2][5]. For the zinc(II) chelation, the reaction was changed from a reaction

Cross-linked cyclodextrin-based material for treatment of metals and organic substances present in industrial discharge waters

• Élise Euvrard,
• Nadia Morin-Crini,
• Coline Druart,
• Justine Bugnet,
• Bernard Martel,
• Cesare Cosentino,
• Virginie Moutarlier and
• Grégorio Crini

Beilstein J. Org. Chem. 2016, 12, 1826–1838, doi:10.3762/bjoc.12.172

• substances in DWs). For this purpose, specific systems can be added, called effluent finishing treatments. A sequential dual approach can be considered: firstly, adsorption onto carbon to remove organics (e.g., solvents, oils, PAHs and volatile organic compounds) combined with ion-exchange and/or chelation

Total synthesis of leopolic acid A, a natural 2,3-pyrrolidinedione with antimicrobial activity

• Atul A. Dhavan,
• Rahul D. Kaduskar,
• Loana Musso,
• Leonardo Scaglioni,
• Piera Anna Martino and
• Sabrina Dallavalle

Beilstein J. Org. Chem. 2016, 12, 1624–1628, doi:10.3762/bjoc.12.159

• reduction is in agreement with previous results and is consistent with the Cram model for a chelation controlled reduction [16][17][18]. Both OH groups of compound 9 were oxidized by PCC to obtain aldehyde 10. The long carbon chain was incorporated into 10 by Wittig olefination with n

Chiral cyclopentadienylruthenium sulfoxide catalysts for asymmetric redox bicycloisomerization

• Barry M. Trost,
• Michael C. Ryan and
• Meera Rao

Beilstein J. Org. Chem. 2016, 12, 1136–1152, doi:10.3762/bjoc.12.110

• chelation effect wherein the o-methoxy group acts as a hemilabile ligand, changing the steric and electronic environment around the metal center. Since 20 displayed inferior conversions and yields, however, it was eschewed in favor of complex 1. Cyclohexyl 21 was also an excellent catalyst in terms of

Diastereoselective synthesis of new O-alkylated and C-branched inositols and their corresponding fluoro analogues

• Charlotte Collet,
• Françoise Chrétien,
• Yves Chapleur and
• Sandrine Lamandé-Langle

Beilstein J. Org. Chem. 2016, 12, 353–361, doi:10.3762/bjoc.12.39

• selectivity of this reduction was lower compared to previously published results [43]. A diastereoisomeric ratio of 4:1 myo-8/scyllo-8 was estimated by 1H NMR when the same reduction was done in a dichloromethane/methanol mixture. This selectivity can be explained by a chelation of the sodium ion with the two

New metathesis catalyst bearing chromanyl moieties at the N-heterocyclic carbene ligand

• Agnieszka Hryniewicka,
• Szymon Suchodolski,
• Agnieszka Wojtkielewicz,
• Jacek W. Morzycki and
• Stanisław Witkowski

Beilstein J. Org. Chem. 2015, 11, 2795–2804, doi:10.3762/bjoc.11.300

• complex compared to other catalysts. It may favour chelation of the ruthenium centre of the catalyst by the carbonyl ester oxygen from the diene substrate. It seems that the oxygen–ruthenium bond is rather labile. The oxygen coordination does not decrease the activity of the catalyst but rather stabilises

Easy access to heterobimetallic complexes for medical imaging applications via microwave-enhanced cycloaddition

• Nicolas Desbois,
• Sandrine Pacquelet,
• Adrien Dubois,
• Clément Michelin and
• Claude P. Gros

Beilstein J. Org. Chem. 2015, 11, 2202–2208, doi:10.3762/bjoc.11.239

• first dissolved in trifluoroacetic acid (TFA) and stirred at room temperature overnight. A brown oil was obtained upon concentration. The residue was then purified by flash chromatography. Chelation of Cu2+ with propargyl NOTA 4 was performed in aqueous solution by Cu(ClO4)2·6H2O. Purification of Cu

A comprehensive study of olefin metathesis catalyzed by Ru-based catalysts

• Albert Poater and
• Luigi Cavallo

Beilstein J. Org. Chem. 2015, 11, 1767–1780, doi:10.3762/bjoc.11.192

• on the cis/trans preference for 12, whereas for 11 trans coordination of C2H4 is not favored. This is easily explained by considering that the 5-membered ring formed through chelation of the cresol group to Ru makes a trans O–Ru–O disposition geometrically difficult, whereas the 6-membered ring

• formed by chelation of the sulfoxide ligand in 12 allows for a trans O–Ru–O geometry with little steric strain. 12 presents three cis isomers, denoted as C(S1), C(S2), and C(O) in Table 2, which correspond to have the phenolic or the sulfonic O atom trans to the NHC ligand (see Figure 1). Our

The facile construction of the phthalazin-1(2H)-one scaffold via copper-mediated C–H(sp²)/C–H(sp) coupling under mild conditions

• Wei Zhu,
• Bao Wang,
• Shengbin Zhou and
• Hong Liu

Beilstein J. Org. Chem. 2015, 11, 1624–1631, doi:10.3762/bjoc.11.177

• recovered in good yield. Based on previous works [22][23][25], a copper(II)-mediated C–H functionalization pathway is proposed in Scheme 5. A base-promoted cupration of the relatively acidic C–H of ethynylbenzene provides ethynylcopper intermediate M1. The following bidentate chelation with 1a yields

Diastereoselective and enantioselective conjugate addition reactions utilizing α,β-unsaturated amides and lactams

• Katherine M. Byrd

Beilstein J. Org. Chem. 2015, 11, 530–562, doi:10.3762/bjoc.11.60

• the oxygen of the resulting enolate of the CA reaction. This chelation to the magnesium would retard the 1,2-addition reaction from occurring. Since the Mukaiyama publication, there have been many chiral auxiliaries studied in DCA reactions of α,β-unsaturated amides [35]. Figure 2 highlights a few of

Chemoselective O-acylation of hydroxyamino acids and amino alcohols under acidic reaction conditions: History, scope and applications

• Tor E. Kristensen

Beilstein J. Org. Chem. 2015, 11, 446–468, doi:10.3762/bjoc.11.51

• that amino acid chemistry has fostered the development of a number of specialized methodologies to handle the manifold functional groups present in the most common amino acids. A salient example is the copper chelation chemistry originally introduced by Kurtz in 1941 to isolate lysine from protein

• liberating the acylated derivative from its copper salt using 8-hydroxyquinoline as an organic chelating precipitant [8]. While both useful and creative, the copper chelation procedure carries with it many of the same shortcomings as other types of protective group chemistry. However, by a change of the

A versatile δ-aminolevulinic acid (ΑLA)-cyclodextrin bimodal conjugate-prodrug for PDT applications with the help of intracellular chemistry

• Chrysie Aggelidou,
• Theodossis A. Theodossiou,
• Antonio Ricardo Gonçalves,
• Mariza Lampropoulou and
• Konstantina Yannakopoulou

Beilstein J. Org. Chem. 2014, 10, 2414–2420, doi:10.3762/bjoc.10.251

• cancerous rather than squamous tissues [1]. δ-Aminolevulinic acid (1, ALA, Scheme 1) is a δ-amino acid precursor in the cellular biosynthesis of heme [2]. The penultimate step in this biosynthetic cycle is the iron chelation of protoporphyrin IX (PpIX), a porphyrin photosensitizer (PS) which was shown to be

Efficient CO₂ capture by tertiary amine-functionalized ionic liquids through Li⁺-stabilized zwitterionic adduct formation

• Zhen-Zhen Yang and
• Liang-Nian He

Beilstein J. Org. Chem. 2014, 10, 1959–1966, doi:10.3762/bjoc.10.204

• cations derived from chelation between neutral ligands and Li+ are shown in Figure 1. The geometry optimizations were carried out by performing DFT calculations. Four O atoms in PEG150Me chelate with Li+ in a quasi-crown ether manner. For neutral ligands with PEG chain (PEG150MeIm, PEG150MeNH2

• cycles. Typical optimized structures of complex cations derived from chelation between Li+ and neutral ligands. H: white, C: grey, O: red, N: blue, Li: purple. Bond lengths are in Å. (a) Comparison of the thermal stability between the neutral ligands and the corresponding chelated ionic liquids after

Synthesis of the first examples of iminosugar clusters based on cyclopeptoid cores

• Mathieu L. Lepage,
• Alessandra Meli,
• Anne Bodlenner,
• Céline Tarnus,
• Francesco De Riccardis,
• Irene Izzo and
• Philippe Compain

Beilstein J. Org. Chem. 2014, 10, 1406–1412, doi:10.3762/bjoc.10.144

• bonds, which can isomerize more readily than secondary amides, and to the absence of amide protons, which stabilize secondary structure by backbone hydrogen bonding [15][16]. As we have previousy demonstrated, this heterogeneity can be reduced by metal chelation [35][38]. Addition of an excess of sodium

Automated solid-phase peptide synthesis to obtain therapeutic peptides

• Veronika Mäde,
• Sylvia Els-Heindl and
• Annette G. Beck-Sickinger

Beilstein J. Org. Chem. 2014, 10, 1197–1212, doi:10.3762/bjoc.10.118

• -histidinyl acetyl (NαHis-ac) chelator (Figure 5) was attached to lysine side chains or the N-terminus of the peptide by manual coupling, whereas the chelation with 99mTc occurred in solution [133]. The incorporation of carbaboranes that can be used for boron neutron capture therapy demonstrated the potential

Silver and gold-catalyzed multicomponent reactions

• Giorgio Abbiati and
• Elisabetta Rossi

Beilstein J. Org. Chem. 2014, 10, 481–513, doi:10.3762/bjoc.10.46

• chiral phosphine ligands and AgOAc via bidentate chelation of a properly substituted aldimine. Chiral phosphine–silver(I) complexes are emerging as a valuable tool for carbon–carbon bond forming reactions. These catalysts are effective in promoting enantioselective allylations, aldol reactions, Mannich

• bidentate chelation (Scheme 36). The substrate is bound anti to the bulky amino acid substituent (R) and reacts with the siloxyfuran via endo-type addition. Intramolecular silyl transfer, iPrOH mediated desilylation of the amide terminus, and protonation of the N–Ag bond delivers the final product and the

Garner’s aldehyde as a versatile intermediate in the synthesis of enantiopure natural products

• Mikko Passiniemi and
• Ari M.P. Koskinen

Beilstein J. Org. Chem. 2013, 9, 2641–2659, doi:10.3762/bjoc.9.300

• . Depending on the stereofacial selectivity, one can access either the anti-isomer 12 or syn-isomer 13 as the major product (Scheme 7). The high anti-selectivity can be rationalized with the attack of the nucleophile from the sterically least hindered side (re-side attack). The Felkin–Anh non-chelation

• density from the reaction center toward nitrogen. In cases where syn-selectivity is observed, the Cram’s chelation control model provides an explanation [56][57]. Chelating metal coordinates between the two carbonyls (the aldehyde and the carbamate), thus forcing the nucleophile to attack from the si-side

• syn-selectivities were achieved with vinylZnCl in Et2O (1:6 anti/syn). Coleman also noticed that the addition of excess ZnCl2 did not increase the syn-selectivity at all. They attributed this to the mono-coordination of the metal to the carbamate instead of the usual “bidentate” chelation control

Regioselective carbon–carbon bond formation of 5,5,5-trifluoro-1-phenylpent-3-en-1-yne

• Motoki Naka,
• Tomoko Kawasaki-Takasuka and
• Takashi Yamazaki

Beilstein J. Org. Chem. 2013, 9, 2182–2188, doi:10.3762/bjoc.9.256

• electrophiles, under equilibration of the possible two anionic species. Keywords: additives; computation; Li···F chelation; deprotonation; electron-withdrawing effect; organo-fluorine; Introduction We have previously reported [1] the interesting behavior of (E)-1-chloro-3,3,3-trifluoropropene ((E)-1) [2][3][4

• initial Hb abstraction from (E)-1 and the resultant Int-1 was stabilized by the energetically favorable 5-membered intramolecular Li···F chelation [5]. This intermediate Int-1 experienced Fritsch–Buttenberg-Wiechell (FBW) rearrangement [6][7] to give 3,3,3-trifluoropropyne, and Int-2 derived from this

• ] of the trans-disposed chlorine atom. However, it is also likely that the anionic intermediate produced after Hb abstraction would prefer the reaction course to 2 by way of FBW rearrangement because of its lower stability than Int-1 with loss of the possibility for Li···F chelation. It was not only

An approach towards azafuranomycin analogs by gold-catalyzed cycloisomerization of allenes: synthesis of (αS,2R)-(2,5-dihydro-1H-pyrrol-2-yl)glycine

• Jörg Erdsack and
• Norbert Krause

Beilstein J. Org. Chem. 2013, 9, 1936–1942, doi:10.3762/bjoc.9.229

• ) was carried out (Scheme 5). The aldehyde (R)-2, which was prepared from D-serine [42][43][44], underwent chelation-controlled nucleophilic addition of metallated alkyne 3 [45] to give the propargyl alcohol 14 in 84% yield and a syn-diastereoselectivity of >95:5 [7][46][47]. After tosylation of 14 (85

A reductive coupling strategy towards ripostatin A

• Kristin D. Schleicher and
• Timothy F. Jamison

Beilstein J. Org. Chem. 2013, 9, 1533–1550, doi:10.3762/bjoc.9.175

• most likely candidate for chelation is the oxygen protected as the PMB ether. Although an eight-membered chelate might seem too large to play an important role in directing regioselectivity, the 3:1 regioselectivity observed in the “normal” direction is consistent with chelation playing a diminished