Recent applications of chiral calixarenes in asymmetric catalysis

• Mustafa Durmaz,
• Erkan Halay and
• Selahattin Bozkurt

Beilstein J. Org. Chem. 2018, 14, 1389–1412, doi:10.3762/bjoc.14.117

• six-membered-ring transition state similar to that described earlier by Feng et al. [69]. Epoxidation In 2014 Sciotto et al. reported the synthesis of two novel calix[4]arene–salen ligands 105a,b in 1,3-alternate conformation. Reaction of the salen ligands with appropriate metal acetate salt according

• coligand, their uranyl-(salen) derivatives 106a,b have been employed as models of the oxo-Mn(V)–(salen) oxidant species. The reactions were highly efficient in terms of productivity (up to 96% yield) and enantioselectivity (up to 93% ee) when rigid bicyclic alkenes such as 1,2-dihydronaphthalene and

• calix[4]arene–(salen) complexes. Enantioselective epoxidation of 108 catalyzed by 107a/107b. Synthesis of inherently chiral calix[4]arene catalysts 111 and 112. Enantioselective MPV reduction. Synthesis of chiral calix[4]arene ligands 116a–c. Asymmetric MPV reduction with chiral calix[4]arene ligands

Recent developments in the asymmetric Reformatsky-type reaction

• Hélène Pellissier

Beilstein J. Org. Chem. 2018, 14, 325–344, doi:10.3762/bjoc.14.21

• ketones with ethyl iodoacetate performed with enantioselectivities of up to 86% ee in the presence of a chiral manganese salen complex [36]. The same year, this author also described the first catalytic enantioselective aza-Reformatsky reaction between in situ generated imines and ethyl iodoacetate [37

Solvent-free sonochemistry: Sonochemical organic synthesis in the absence of a liquid medium

• Deborah E. Crawford

Beilstein J. Org. Chem. 2017, 13, 1850–1856, doi:10.3762/bjoc.13.179

• sonochemical reactions being carried out in the absence of solvent, or a liquid reagent [8][9]. Herein, we report two condensation reactions (investigated extensively by ball milling), one to form salen ligand 1 by sonicating o-vanillin and 1,2-phenylenediamine, and the second to form 1,3-indandione 2 from

Exploring endoperoxides as a new entry for the synthesis of branched azasugars

• Svenja Domeyer,
• Mark Bjerregaard,
• Henrik Johansson and
• Daniel Sejer Pedersen

Beilstein J. Org. Chem. 2017, 13, 644–647, doi:10.3762/bjoc.13.63

• anticipated that the reaction conditions could be optimised to favour the desired diol product. Ring contraction of acetonide-protected endoperoxide 23 by treatment with triphenylphosphine provided ready access to tetrahydrofuran 24 in good yield [21]. Finally, treatment of endoperoxide 23 with Co(salen) gave

Extrusion – back to the future: Using an established technique to reform automated chemical synthesis

• Deborah E. Crawford

Beilstein J. Org. Chem. 2017, 13, 65–75, doi:10.3762/bjoc.13.9

• heating (right). Taken from [44]. Synthesis of Ni(NCS)2(PPh3)2 and [Ni(salen)] by twin screw extrusion. Adapted from [2]. Polymerisation of styrene using s-BuLi as an initiator. Telescoping process of the formation of polystyrene, followed by post polymerisation functionalisation with isoprene. The figure

Chromium(II)-catalyzed enantioselective arylation of ketones

• Gang Wang,
• Shutao Sun,
• Ying Mao,
• Zhiyu Xie and
• Lei Liu

Beilstein J. Org. Chem. 2016, 12, 2771–2775, doi:10.3762/bjoc.12.275

• addition reactions mainly focused on allylation, propargylation, alkenylation and alkylation of aldehydes [10][11]. Since the first example of enantioselective allylation of aldehydes catalyzed by a Cr(II)–salen complex in 1999 by Cozzi and co-workers [12], several elegant catalytic enantioselective

Rearrangements of organic peroxides and related processes

• Ivan A. Yaremenko,
• Vera A. Vil’,
• Dmitry V. Demchuk and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2016, 12, 1647–1748, doi:10.3762/bjoc.12.162

Recent advances in metathesis-derived polymers containing transition metals in the side chain

• Ileana Dragutan,
• Valerian Dragutan,
• Bogdan C. Simionescu,
• Albert Demonceau and
• Helmut Fischer

Beilstein J. Org. Chem. 2015, 11, 2747–2762, doi:10.3762/bjoc.11.296

• between the metal and the organic polymer backbone and/or side chains is crucial for ensuring the desired properties for the hybrid material [68]. Indeed, when appraising luminescence of a series of polynorbornenes attaching various homoleptic bi- or trinuclear lanthanide salen complexes (with La, Nd, Yb

Pyridylidene ligand facilitates gold-catalyzed oxidative C–H arylation of heterocycles

• Kazuhiro Hata,
• Hideto Ito,
• Yasutomo Segawa and
• Kenichiro Itami

Beilstein J. Org. Chem. 2015, 11, 2737–2746, doi:10.3762/bjoc.11.295

• -catalyzed reactions, phosphines, N-heterocyclic carbenes, pyridines and salen ligands have been applied as ligands for controlling the stability of catalysts, and chemo-, regio- and enantioselectivities of the reactions [31][32][33][34][35][36]. Recent advances in the gold-catalyzed reactions are

Robust bifunctional aluminium–salen catalysts for the preparation of cyclic carbonates from carbon dioxide and epoxides

• Yuri A. Rulev,
• Zalina Gugkaeva,
• Victor I. Maleev,
• Michael North and
• Yuri N. Belokon

Beilstein J. Org. Chem. 2015, 11, 1614–1623, doi:10.3762/bjoc.11.176

• one-component aluminium-based catalysts for the reaction between epoxides and carbon dioxide have been prepared. The catalysts are composed of aluminium–salen chloride complexes with trialkylammonium groups directly attached to the aromatic rings of the salen ligand. With terminal epoxides, the

• mixture and reused. Keywords: aluminium; carbon dioxide; cyclic carbonate; epoxide; salen; Introduction Carbon dioxide is a renewable and inexpensive carbon source, so great efforts have been directed at developing novel methods for the valorization of this abundant raw material [1]. One way of

• developed for the production of cyclic carbonates [7][8][9] and polycarbonates [10][11] from carbon dioxide and epoxides, the most developed and privileged set of catalysts are based on Lewis acidic metal–salen complexes. In particular, cobalt(III) and chromium(III) complexes were found to be highly

Surprisingly facile CO₂ insertion into cobalt alkoxide bonds: A theoretical investigation

• Willem K. Offermans,
• Claudia Bizzarri,
• Walter Leitner and
• Thomas E. Müller

Beilstein J. Org. Chem. 2015, 11, 1340–1351, doi:10.3762/bjoc.11.144

• calculations to elucidate the reaction step of CO2 insertion into cobalt(III)–alkoxide bonds, which is also the central step of metal catalysed carboxylation reactions. It was found that CO2 insertion into the cobalt(III)–alkoxide bond of [(2-hydroxyethoxy)CoIII(salen)(L)] complexes (salen = N,N”-bis

• , a linear Brønsted–Evans–Polanyi relationship was found between the activation energy and the reaction energy. Keywords: activation; alkoxide; carbon dioxide; cobalt; insertion; salen; Introduction Carbon dioxide (CO2) has been known to be an attractive carbon source for decades [1][2][3][4][5][6

• – [13][14][15][16][17][18] and cobalt–salen complexes [19][20][21][22] and heterogeneous double metal cyanide (DMC) catalysts [11][23][24][25][26]. In comparison, industrially well-established catalysts are available to accelerate the production of cyclic carbonates [27][28][29]. As the CO2-based

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

• ] and biological chemistry [249][250][251][252]. In the past, the Jacobsen group has used chiral (salen)Al complexes [253] as catalysts for the asymmetric 1,4-addition of azide [254], cyanide [219], substituted nitriles [255] and oximes [256] to α,β-unsaturated imides. The authors used these previous

Anion effect controlling the selectivity in the zinc-catalysed copolymerisation of CO₂ and cyclohexene oxide

• Sait Elmas,
• Muhammad Afzal Subhani,
• Walter Leitner and
• Thomas E. Müller

Beilstein J. Org. Chem. 2015, 11, 42–49, doi:10.3762/bjoc.11.7

• secondary amino and two phenoxy donor groups [17]. The binuclear Zn(II) complex ([LZn2X2], X = acetate) is substrate specific for the copolymerisation of CO2 and cyclohexene oxide [16]. Another established common structural motif is based on Salen-type ligands with a central Co(III) [18][19][20] or Cr(III

• ) [21][22][23][24] atom (Type II). Most catalysts based on Salen-type ligands are substrate specific and are most efficient for the copolymerisation of CO2 with propylene oxide (PO). The use of zinc-based catalysts of Type I appears more favourable from an environmental perspective compared to the use

• : mononuclear complexes with a Salen ligand. Binuclear Zn(II) complexes [LZn2](CF3SO3)2 (1, KOP113) and [LZn2](p-TSO3)2 (2, KOP115) explored in this study (the numbers refer to the assignment of the NMR signals, see also Table 1). Copolymerisation of CO2 and cyclohexene oxide (*: end groups of the polymer chain

Oligomerization of optically active N-(4-hydroxyphenyl)mandelamide in the presence of β-cyclodextrin and the minor role of chirality

• Helmut Ritter,
• Antonia Stöhr and
• Philippe Favresse

Beilstein J. Org. Chem. 2014, 10, 2361–2366, doi:10.3762/bjoc.10.246

• the oligomerization of substituted electron-rich phenols in the presence of oxidizing agents [3][4]. In addition to that, N,N'-bis(salicylidene)ethylenediamine-iron(II) (iron(II)-salen) represents an alternative catalyst for oxidative coupling reactions of phenol derivatives [5]. The use of β

• from horseradish or iron(II)-salen were used as catalysts. The obtained yellow powdery oligomers 2 show high solubility in many commonly used organic solvents like acetone, THF, ethanol, methanol, acetonitrile and 1,4-dioxan. Because of the broad signals of the oligomers 2 in the 1H NMR spectra the

• enzymatic oligomerization consists of up to 10 repetitive units which could be detected by MALDI–TOF MS measurements. Furthermore comparable molecular weights are accessible through oligomerization of 1 with iron(II)-salen as catalyst. Here oligomers 2 with up to 8 repetitive units are detectable. The

Comparing kinetic profiles between bifunctional and binary type of Zn(salen)-based catalysts for organic carbonate formation

• Carmen Martín and
• Arjan W. Kleij

Beilstein J. Org. Chem. 2014, 10, 1817–1825, doi:10.3762/bjoc.10.191

• Carmen Martin Arjan W. Kleij Institute of Chemical Research of Catalonia (ICIQ), Av. Països Catalans 16, 43007 Tarragona, Spain Catalan Institute for Research and Advanced Studies (ICREA), Pg. Lluis Companys 23, 08010 Barcelona, Spain 10.3762/bjoc.10.191 Abstract Zn(salen) complexes have been

• opposed to the binary catalyst that is connected with a first-order dependence on the catalyst concentration and a monometallic mechanism. Keywords: CO2 chemistry; cyclic carbonates; kinetic studies; salen complexes; zinc; Introduction Carbon dioxide may be regarded as an ideal, renewable carbon feed

• , nontoxic and earth-abundant metal-based complexes based on aluminum [24] and iron [25] amino-triphenolate complexes. Additionally, salen-based Zn complexes were also found to be rather efficient catalyst for this transformation. More specifically, these systems relate to the Zn(salphen) family of complexes

Copolymerization and terpolymerization of carbon dioxide/propylene oxide/phthalic anhydride using a (salen)Co(III) complex tethering four quaternary ammonium salts

• Jong Yeob Jeon,
• Seong Chan Eo,
• Jobi Kodiyan Varghese and
• Bun Yeoul Lee

Beilstein J. Org. Chem. 2014, 10, 1787–1795, doi:10.3762/bjoc.10.187

• Jong Yeob Jeon Seong Chan Eo Jobi Kodiyan Varghese Bun Yeoul Lee Department of Molecular Science and Technology, Ajou University, Suwon 443-749 Korea 10.3762/bjoc.10.187 Abstract The (salen)Co(III) complex 1 tethering four quaternary ammonium salts, which is a highly active catalyst in CO2

• with epoxides [1][2][3][4][5][6]. The pioneering work for this copolymerization was introduced by Inoue in 1969 [7]. Eventually, a highly active and efficient catalyst was developed based on the concept of combining (salen)Co(III) units with quaternary ammonium salts in a molecule [8][9][10][11][12

• using a diiminate zinc catalyst as well as a chromium(III) salen complex have been reported [26][27]. Long reaction times (>10 h) were needed to reach full conversion, and the average molecular weights were in the region of several ten thousand. When a zinc glutarate catalyst was used in PO/PA

Isocyanide-based multicomponent reactions towards cyclic constrained peptidomimetics

• Gijs Koopmanschap,
• Eelco Ruijter and
• Romano V.A. Orru

Beilstein J. Org. Chem. 2014, 10, 544–598, doi:10.3762/bjoc.10.50

• ) is easily evaporated. Based on this Passerini reaction, the group of Zhu developed an enantioselective approach using hydrazoic acid as the azide source and [(salen)AlIIIMe] as the catalyst [123]. A variety of aliphatic aldehydes and both aliphatic and aromatic isocyanides were tolerated in their

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

• [Au(III)salen] [20] and [Au(III)(2-phenylpyridine)Cl2] [21] complexes, immobilized heterogeneous catalysts [22], and gold nanoparticles (Au NP) [23][24][25][26] have been reported until 2010, as well as recognized in two recent exhaustive reviews by Li [2] and Van der Eycken [3]. In the past three

• , N-benzylimines and acid chlorides. The reaction was catalyzed by a Au(III)–salen complex 22 and occurred in acetonitrile at 170 °C under dielectric heating (Scheme 15). On the basis of the results of some smart kinetic experiments on ad-hoc synthetized plausible intermediates (III and V) in the

Development of the titanium–TADDOLate-catalyzed asymmetric fluorination of β-ketoesters

• Lukas Hintermann,
• Mauro Perseghini and
• Antonio Togni

Beilstein J. Org. Chem. 2011, 7, 1421–1435, doi:10.3762/bjoc.7.166

• coworkers were able to open meso-epoxides asymmetrically with HF equivalents and chiral chromium–salen complexes [25][26]. In the year 2000, two conceptually different applications of Banks’ electrophilic fluorinating reagent F–TEDA (1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis

Studies on Pd/NiFe₂O₄ catalyzed ligand-free Suzuki reaction in aqueous phase: synthesis of biaryls, terphenyls and polyaryls

• Sanjay R. Borhade and
• Suresh B. Waghmode

Beilstein J. Org. Chem. 2011, 7, 310–319, doi:10.3762/bjoc.7.41

• of phosphorous ligands. Efforts have been made to enhance the catalytic activity by the use of various ligands containing nitrogen or sulfur, as well as phosphines, salen and N-heterocyclic carbenes in traditional organic solvents [12][13][14][15][16][17][18][19]. However, the problems associated

Kinetics and mechanism of vanadium catalysed asymmetric cyanohydrin synthesis in propylene carbonate

• Michael North and
• Marta Omedes-Pujol

Beilstein J. Org. Chem. 2010, 6, 1043–1055, doi:10.3762/bjoc.6.119

• synthesis of cyanohydrin trimethylsilyl ethers from aldehydes and trimethylsilyl cyanide catalysed by VO(salen)NCS, though reactions are slower in this solvent than the corresponding reactions carried out in dichloromethane. A mechanistic study has been undertaken, comparing the catalytic activity of VO

• (salen)NCS in propylene carbonate and dichloromethane. Reactions in both solvents obey overall second-order kinetics, the rate of reaction being dependent on the concentration of both the aldehyde and trimethylsilyl cyanide. The order with respect to VO(salen)NCS was determined and found to decrease from

• 1.2 in dichloromethane to 1.0 in propylene carbonate, indicating that in propylene carbonate, VO(salen)NCS is present only as a mononuclear species, whereas in dichloromethane dinuclear species are present which have previously been shown to be responsible for most of the catalytic activity. Evidence

Molecular recognition of organic ammonium ions in solution using synthetic receptors

• Andreas Späth and
• Burkhard König

Beilstein J. Org. Chem. 2010, 6, No. 32, doi:10.3762/bjoc.6.32

Prediction of reduction potentials from calculated electron affinities for metal-salen compounds

• Sarah B. Bateni,
• Kellie R. England,
• Anthony T. Galatti,
• Handeep Kaur,
• Victor A. Mendiola,
• Alexander R. Mitchell,
• Michael H. Vu,
• Benjamin F. Gherman and
• James A. Miranda

Beilstein J. Org. Chem. 2009, 5, No. 82, doi:10.3762/bjoc.5.82

• Abstract The electron affinities (EAs) of a training set of 19 metal-salen compounds were calculated using density functional theory. Concurrently, the experimental reduction potentials for the training set were measured using cyclic voltammetry. The EAs and reduction potentials were found to be linearly

• could be used to predict the reduction potentials of a variety of metal-salen compounds, an important class of coordination compounds used in synthetic organic electrochemistry as electrocatalysts. Keywords: density functional theory; electron affinity; metal-salen; reduction potential; Introduction

• and the acceptor unit [1]. The ERC reaction has been applied towards the total synthesis of many complex natural products, including quadrone and phorbol [2][3]. Previously, it has been shown that Ni(II)-salen can serve as an electrochemical mediator in the ERC reaction [4]. The most significant

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

Beilstein J. Org. Chem. 2009, 5, No. 33, doi:10.3762/bjoc.5.33

• was prepared in 94.7% ee by asymmetric ring opening of the corresponding N-Boc protected meso epoxide using the Jacobsen (salen)Cr(III) complex and TMSN3 [111]. The acetate group was installed on the aromatic using a palladium catalyzed reaction with the silylketene acetal 140 in the presence of

From discovery to production: Scale- out of continuous flow meso reactors

• Peter Styring and
• Ana I. R. Parracho

Beilstein J. Org. Chem. 2009, 5, No. 29, doi:10.3762/bjoc.5.29

• environmental and economic burden on the process. Previously, we have described a series of catalysts based on nickel(II) and palladium(II) that have functionalised salen-acac (salenac) ligands that were functionalised such that they could be covalently bound to organic or inorganic polymer supports [6][7][8][9