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Search for "squaramide" in Full Text gives 39 result(s) in Beilstein Journal of Organic Chemistry.

A novel recyclable organocatalyst for the gram-scale enantioselective synthesis of (S)-baclofen

  • Gyula Dargó,
  • Dóra Erdélyi,
  • Balázs Molnár,
  • Péter Kisszékelyi,
  • Zsófia Garádi and
  • József Kupai

Beilstein J. Org. Chem. 2023, 19, 1811–1824, doi:10.3762/bjoc.19.133

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  • , application, and recycling of a new lipophilic cinchona squaramide organocatalyst. The synthesized lipophilic organocatalyst was applied in Michael additions. The catalyst was utilized to promote the Michael addition of cyclohexyl Meldrum’s acid to 4-chloro-trans-β-nitrostyrene (quantitative yield, up to 96
  • , acetonitrile, with 91–100% efficiency, and the catalyst was reused in five reaction cycles without the loss of activity and selectivity. Keywords: baclofen; catalyst recovery; lipophilic cinchona squaramide; organocatalysis; stereoselective catalysis; Introduction In today’s chemical industry, catalytic
  • cinchona squaramide organocatalyst. Its catalytic activity and recyclability were examined in a new stereoselective synthesis of baclofen, which is used to treat muscle spasms [30]. Finally, the catalyst was easily recycled by centrifugation over five reaction cycles without significant loss of activity
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Published 24 Nov 2023

N-Sulfenylsuccinimide/phthalimide: an alternative sulfenylating reagent in organic transformations

  • Fatemeh Doraghi,
  • Seyedeh Pegah Aledavoud,
  • Mehdi Ghanbarlou,
  • Bagher Larijani and
  • Mohammad Mahdavi

Beilstein J. Org. Chem. 2023, 19, 1471–1502, doi:10.3762/bjoc.19.106

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  • thiiranium ion by the tosylamide and deprotonation led to the final product 99 or 100 (Scheme 41). Through the coupling reaction of N-(aryl/alkylthio)succinimides 1 with 5H-oxazol-4-ones 101 in the presence of an organocatalyst named cinchona alkaloid-derived squaramide F, a series of α-sulfenylated products
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Published 27 Sep 2023
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  • investigated to install the all-substituted aza-quaternary stereocenter at the C4 position of the pyrazolinone scaffold. Stereoinduction on this chiral center was regulated by the chiral squaramide catalyst S1 affording the products with excellent enantioselectivities. A stereodefined transition state
  • developed an aza-Friedel–Crafts reaction involving β-naphthols 119 as π-nucleophiles and benzothiazolimines 118 as electrophiles. Chiral squaramide S1-assisted this process affording enantioenriched 1-((benzothiazol-2-ylamino)methyl)naphthalen-2-ols 120 with high chemical yields. The activation of the
  • . Atroposelective aza-Friedel–Crafts reaction. Coupling of 5-aminopyrazole and 3H-indol-3-ones. Pyrophosphoric acid-catalyzed aza-Friedel–Crafts reaction on phenols. Squaramide-assisted aza-Friedel–Crafts reaction. Thiourea-catalyzed aza-Friedel–Crafts reaction. Squaramide-catalyzed reaction between β-naphthols and
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Published 28 Jun 2023

Catalytic aza-Nazarov cyclization reactions to access α-methylene-γ-lactam heterocycles

  • Bilge Banu Yagci,
  • Selin Ezgi Donmez,
  • Onur Şahin and
  • Yunus Emre Türkmen

Beilstein J. Org. Chem. 2023, 19, 66–77, doi:10.3762/bjoc.19.6

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  • (Table 1, entry 11). With this promising result in hand, we next examined the use of squaramides, which were shown to be highly effective hydrogen-bonding catalysts in a broad range of transformations [61][62][63][64]. When achiral squaramide derivatives 11 [65] and 12 [66] were tested in stoichiometric
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Published 17 Jan 2023

Total synthesis of grayanane natural products

  • Nicolas Fay,
  • Rémi Blieck,
  • Cyrille Kouklovsky and
  • Aurélien de la Torre

Beilstein J. Org. Chem. 2022, 18, 1707–1719, doi:10.3762/bjoc.18.181

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  • optimization showed that chiral squaramide 47 developed by Jacobsen’s group significantly accelerated the Mukaiyama reaction compared to TMSOTf or TiCl4 thanks to chiral hydrogen bond-donor effect [35]. After Sakurai cyclization promoted by EtAlCl2, the desired product 48 was obtained with the required
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Published 12 Dec 2022

New advances in asymmetric organocatalysis

  • Radovan Šebesta

Beilstein J. Org. Chem. 2022, 18, 240–242, doi:10.3762/bjoc.18.28

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  • nitromethane to β-silyl α,β-unsaturated carbonyl compounds catalyzed by bifunctional squaramide catalysts are effective under solvent-free conditions [26]. Zhai and Du demonstrated that asymmetric [3 + 2] annulation reactions of 2-isothiocyanato-1-indanones with barbiturate-based olefins are efficiently
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Published 28 Feb 2022

Organocatalytic asymmetric nitroso aldol reaction of α-substituted malonamates

  • Ekta Gupta,
  • Narendra Kumar Vaishanv,
  • Sandeep Kumar,
  • Raja Krishnan Purshottam,
  • Ruchir Kant and
  • Kishor Mohanan

Beilstein J. Org. Chem. 2022, 18, 217–224, doi:10.3762/bjoc.18.25

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  • reported a squaramide-catalyzed asymmetric nitroso aldol reaction of cyclic β-ketoesters and malonamate [61]. Inspired by this, we decided to investigate the use of malonamate in the asymmetric nitroso aldol reaction using thiourea catalysis. Herein, we report a novel nitroso aldol reaction of malonamates
  • squaramide catalyst 3c, however, with low enantioselectivity (Table 1, entry 6). Disappointingly, the reaction catalyzed by ʟ-proline-derived catalysts gave very low enantioselectivity (Table 1, entries 7 and 8). Having identified Takemoto’s catalyst as the most efficient one for this transformation, our
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Published 21 Feb 2022

Asymmetric organocatalytic Michael addition of cyclopentane-1,2-dione to alkylidene oxindole

  • Estelle Silm,
  • Ivar Järving and
  • Tõnis Kanger

Beilstein J. Org. Chem. 2022, 18, 167–173, doi:10.3762/bjoc.18.18

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  • presence of a multifunctional squaramide catalyst. Michael adducts were obtained in high enantioselectivities and in moderate diastereoselectivities. Keywords: cyclopentane-1,2-dione; enantioselective catalysis; Michael addition; organocatalysis; squaramide; Introduction Diketones are generally very
  • bifunctional hydrogen-bonding catalyst would activate both CPD via a tertiary amino group of a quinuclidine moiety acting as a base via anion-binding, and an oxindole through the squaramide or thiourea moieties of the catalyst as hydrogen bond donors (Figure 1) [29][30][31][32]. Therefore, squaramide and
  • thiourea catalysts were screened in a model reaction between CPD 1 and Boc-protected benzylidene oxindole 2a at room temperature in the presence of 10 mol % of catalyst (Figure 2). First, the quinidine-derived squaramide A was used and the desired product was obtained as a mixture of chromatographically
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Published 03 Feb 2022

Bifunctional thiourea-catalyzed asymmetric [3 + 2] annulation reactions of 2-isothiocyanato-1-indanones with barbiturate-based olefins

  • Jiang-Song Zhai and
  • Da-Ming Du

Beilstein J. Org. Chem. 2022, 18, 25–36, doi:10.3762/bjoc.18.3

Graphical Abstract
  • . Results and Discussion To verify the feasibility of the reaction, the domino Michael addition/cyclization reaction of 2-isothiocyanato-1-indanone (1a) and barbiturate-based olefin 2a was used as a model reaction, which was carried out in dichloromethane (DCM) with 5 mol % quinine-derived squaramide C1 at
  • results, it was found that the yield of product did not increase significantly with the cinchona alkaloid-derived squaramide catalysts (Table 1, entries 2 and 3). Consequently, we decided to explore the effects of different types of catalysts on the reaction. Through experiments, it can be found that
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Published 04 Jan 2022

Solvent-free synthesis of enantioenriched β-silyl nitroalkanes under organocatalytic conditions

  • Akhil K. Dubey and
  • Raghunath Chowdhury

Beilstein J. Org. Chem. 2021, 17, 2642–2649, doi:10.3762/bjoc.17.177

Graphical Abstract
  • -unsaturated carbonyl compounds catalyzed by bifunctional squaramide catalysts has been developed. This methodology offers both enantiomers of β-silyl nitroalkanes in good to excellent yields (up to 92%) and enantioselectivities (up to 97.5% ee) under solvent-free conditions at room temperature. Control
  • 6). The catalytic performance of the squaramide catalysts was also explored for the model reaction. Catalyst VII afforded the conjugate addition product 3a in 78% yield with excellent enantiopurity of 97% ee (Table 1, entry 7). A solvent survey (see Supporting Information File 1 for details
  • even with better yields while the enantiomeric excess was unperturbed. Conclusion In summary, we have outlined bifunctional squaramide-catalyzed 1,4-conjugate addition reaction of nitromethane to β-silyl α,β-unsaturated carbonyl compounds to access a series of chiral β-silyl nitroalkanes in high yields
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Published 27 Oct 2021

N-Sulfinylpyrrolidine-containing ureas and thioureas as bifunctional organocatalysts

  • Viera Poláčková,
  • Dominika Krištofíková,
  • Boglárka Némethová,
  • Renata Górová,
  • Mária Mečiarová and
  • Radovan Šebesta

Beilstein J. Org. Chem. 2021, 17, 2629–2641, doi:10.3762/bjoc.17.176

Graphical Abstract
  • syntheses, including total syntheses of natural compounds [15]. The pyrrolidine moiety has been successfully combined with thiourea [16][17][18] and the squaramide unit [19][20]. Thioureas and squaramides often feature the electron-withdrawing group attached to one of the nitrogen atoms to increase the
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Published 25 Oct 2021

Recent advances in organocatalytic asymmetric aza-Michael reactions of amines and amides

  • Pratibha Sharma,
  • Raakhi Gupta and
  • Raj K. Bansal

Beilstein J. Org. Chem. 2021, 17, 2585–2610, doi:10.3762/bjoc.17.173

Graphical Abstract
  • compounds; however, in order to comply with the requirements of a mini review, additions of amines and amides only will be included. 1. Non-covalent bonding organocatalytic aza-Michael reactions Organocatalysts catalyzing aza-MRs through mainly hydrogen bonding include cinchona alkaloids, squaramide
  • . It was concluded that the catalytic activity of the MDO was the result of the cooperative action of both constituents. Several examples of such MDOs are included in the paper. The reported yield varies from 56–90% with excellent ee ≈ 99% in all cases. 1.2. Reactions catalyzed by chiral squaramide
  • reactions [34][35]. In 2015, Zhao et al. synthesized spiro[pyrrolidine-3,3'-oxindoles] 29 in single step by asymmetric cascade aza-Michael/Michael addition reaction between 4-tosylaminobut-2-enoates 27 and 3-ylideneoxindoles 26 catalyzed by a chiral bifunctional tertiary amine, squaramide (cat. 28) which
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Published 18 Oct 2021

Base-free enantioselective SN2 alkylation of 2-oxindoles via bifunctional phase-transfer catalysis

  • Mili Litvajova,
  • Emiliano Sorrentino,
  • Brendan Twamley and
  • Stephen J. Connon

Beilstein J. Org. Chem. 2021, 17, 2287–2294, doi:10.3762/bjoc.17.146

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  • , the reactions were carried out under base-free conditions. It was found that urea-based catalysts outperformed squaramide derivatives, and that the installation of a chlorine atom adjacent to the catalyst’s quinoline moiety aided in avoiding selectivity-reducing complications related to the production
  • region of the catalyst led to racemic products (Table 1, entries 6 and 7). Employing a different hydrogen bond-donating motif such as the squaramide (catalyst 8, Table 1, entry 8) resulted in a substantial drop of the enantiocontrol as well as in the reduction of the reaction rate [29][31] – probably due
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Published 02 Sep 2021

Halides as versatile anions in asymmetric anion-binding organocatalysis

  • Lukas Schifferer,
  • Martin Stinglhamer,
  • Kirandeep Kaur and
  • Olga García Macheño

Beilstein J. Org. Chem. 2021, 17, 2270–2286, doi:10.3762/bjoc.17.145

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  • complex or active nucleophiles. In 2014, Jacobsen et al. developed a highly enantioselective selenocyclization reaction of olefins 26, using the chiral squaramide 28 as a dual hydrogen bond donor (Scheme 6) [16]. Although early-stage enantio-enrichment during the introduction of selenium is hard to
  • performances as nucleophile precursors using a triazolium-amide chiral catalyst 34 [21] (Scheme 8a), as well as by Jacobsen in the desymmetrization of oxetanes 35 using TMSBr and squaramide 37 as catalyst [56] (Scheme 8b). For the latter, a more detailed mechanistic study was recently provided [57]. The
  • design of more efficient H-donor catalyst structures, offering additional noncovalent interactions in order to provide extra coordination points with the anion, substrate and/or reagent. The most important approaches in this direction used to date are presented in the following. (Thio)urea and squaramide
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Published 01 Sep 2021

Asymmetric organocatalyzed synthesis of coumarin derivatives

  • Natália M. Moreira,
  • Lorena S. R. Martelli and
  • Arlene G. Corrêa

Beilstein J. Org. Chem. 2021, 17, 1952–1980, doi:10.3762/bjoc.17.128

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  • , provides coumarin derivatives 3 with good to excellent yields and moderate to good enantiomeric excesses (Scheme 5). The authors highlighted that the employed organocatalyst 18 is an alternative to those of squaramide and thiourea commonly used with coumarins. In 2013, Lee et al. reported the
  • , with moderate to excellent enantioselectivity followed by two decarboxylations (Scheme 21). Huang’s group has used azadienes to perform an enantioselective 1,4-addition to afford benzofuran-fused six-membered heterocycles with a squaramide catalyst [56]. Based on their previous work, the authors
  • results were obtained using a squaramide cinchona alkaloid catalyst 73 in only 1 mol % loading. In addition, the reaction was also very efficient in a gram-scale experiment, which demonstrates the applicability of the method (Scheme 22). More recently, Yuan et al. developed a methodology for the synthesis
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Published 03 Aug 2021

Organocatalytic asymmetric Michael/acyl transfer reaction between α-nitroketones and 4-arylidenepyrrolidine-2,3-diones

  • Chandrakanta Parida and
  • Subhas Chandra Pan

Beilstein J. Org. Chem. 2021, 17, 1447–1452, doi:10.3762/bjoc.17.100

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  • presence of the quinine-derived bifunctional squaramide catalyst I in dichloromethane at room temperature (Table 1). Delightfully, after stirring for 12 hours, a product was isolated in 70% yield that was characterized as compound 3a and was supposed to be formed through conjugate addition followed by
  • benzoyl-transfer reaction. However, only 20% enantiomeric excess was achieved. Then, the tert-leucine-derived squaramide catalyst II was employed and here both yield and ee slightly improved. Next, we turned our attention to bifunctional thiourea catalysts [26][27] that proved to be fruitful. Thus, the
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Published 14 Jun 2021

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

  • Guido Gambacorta,
  • James S. Sharley and
  • Ian R. Baxendale

Beilstein J. Org. Chem. 2021, 17, 1181–1312, doi:10.3762/bjoc.17.90

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Published 18 May 2021
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  • building blocks for the construction of more elaborate structures [7][8][9][10][11]. An outstanding class of quinine derived organocatalysts exhibits a bifunctional mode of activation by the incorporation of an acidic unit, such as urea, thiourea, squaramide or sulfonamide moieties, giving rise to the
  • synthesis of new amino-substituted-DMAP-based sulfonamides [39] and quinine-based squaramide-type organocatalysts [40]. Motivated by the excellent results obtained with our aforementioned catalysts, we developed a new chiral bifunctional sulfonamide–quinine organocatalyst that unites both classes. The
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Published 18 Feb 2021

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

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  • rearrangement, we tried to optimize its reaction course under mild conditions using various bases, solvents, and hydrogen-bond-donating catalysts. We also present a computational explanation and NMR kinetic study for the inefficient Ireland–Claisen rearrangement under thiourea and squaramide catalysis. Results
  • catalyst’s action in the rearrangement, we have studied the effect of catalyst loading in the reaction of ester 1c with squaramide C1. The reaction with Et3N as a base and Me3SiOTf without any chiral organocatalyst afforded acid 3c with 74% yield. Repeating the reaction in the presence of squaramide C1 (5
  • of squaramide C1 completely stopped the reaction (Table 3, entry 6). We also studied the effect of the amount of base on the Ireland–Claisen rearrangement of ester 1c in the presence of sulfanediamine C6 (Table 4). The best yield of acid 3c (74%) was recorded with 4.9 equivalents of Et3N without
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Published 10 Dec 2019

Synthesis and supramolecular self-assembly of glutamic acid-based squaramides

  • Juan V. Alegre-Requena,
  • Marleen Häring,
  • Isaac G. Sonsona,
  • Alex Abramov,
  • Eugenia Marqués-López,
  • Raquel P. Herrera and
  • David Díaz Díaz

Beilstein J. Org. Chem. 2018, 14, 2065–2073, doi:10.3762/bjoc.14.180

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  • describe the preparation and characterization of two new unsymmetrical squaramide-based organogelators. The synthesis of the compounds was carried out by subsequent amine condensations starting from dimethyl squarate. The design of the gelators involved a squaramide core connected on one side to a long
  • concentrations and gel-to-sol transition temperatures were also determined for each case. In addition, the superior squaramide diester gelator was compared with an analogue triazole-based gelator in terms of critical gelation concentration, gelation kinetics and thermal phase transition. Keywords: glutamic acid
  • derivative; organogel; self-assembly; squaramide; supramolecular gel; Introduction Since their discovery, squaramides have gained importance across different fields from chemistry to biomedicine due to their synthetic versatility and wide applicability [1]. These compounds, formed by two amine units
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Published 06 Aug 2018

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

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  • both catalysts gave the Michael adduct in excellent yields, high ees were obtained only when 54b was used as organocatalyst (up to 94% ee, Scheme 16). During the last decade, squaramide catalysts have become a powerful alternative to the urea/thiourea and guanidine catalysts as multiple hydrogen bond
  • donors in order to design novel bifunctional catalytic scaffolds [54][55]. Hybrid calixarene hosts bearing bis-squaramide moieties at the endo (or lower) and exo (or upper) rims and their recognition properties toward anionic guests have been already reported [56][57]. Therefore, it would be interesting
  • to investigate the application of chiral calixarene-based squaramides in asymmetric catalysis. Recently, a novel chiral organocatalyst based on the calix[4]arene scaffold carrying squaramide and tertiary amine as catalytic functionalities has been readily developed in two steps from p-tert-butylcalix
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Published 08 Jun 2018

Synthesis of chiral 3-substituted 3-amino-2-oxindoles through enantioselective catalytic nucleophilic additions to isatin imines

  • Hélène Pellissier

Beilstein J. Org. Chem. 2018, 14, 1349–1369, doi:10.3762/bjoc.14.114

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  • -dicarbonyl compounds 5 performed in the presence of chiral cinchona alkaloid-derived squaramide 6 [36]. A range of chiral 3-amino-2-oxindoles 7 was obtained under mild reaction conditions in high to quantitative yields (78–99%) and uniformly excellent enantioselectivities (90–99% ee) as shown in Scheme 2. In
  • diastereoselectivity of 90% de was achieved in the reaction of 1-benzoylacetone (R2 = Me, R3 = Ph) which afforded the corresponding single diastereoisomeric product in 96% yield and 95% ee. In 2018, Tanyeli et al. reinvestigated this type of reactions in the presence of related cinchona alkaloid-derived squaramide
  • asymmetric formal [3 + 2] annulation reaction between N-Boc-isatin imines 3 and 1,4-dithiane-2,5-diol (53) as equal equivalent of 2-mercaptoacetaldehyde [78]. The domino reaction catalyzed by chiral tertiary amine-squaramide catalyst 54 began with the addition of 2-mercaptoacetaldehyde to isatin imine 3
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Published 06 Jun 2018

Investigations towards the stereoselective organocatalyzed Michael addition of dimethyl malonate to a racemic nitroalkene: possible route to the 4-methylpregabalin core structure

  • Denisa Vargová,
  • Rastislav Baran and
  • Radovan Šebesta

Beilstein J. Org. Chem. 2018, 14, 553–559, doi:10.3762/bjoc.14.42

Graphical Abstract
  • medicines and can be obtained by organocatalytic Michael additions. We show here the stereoselective synthesis of 4-methylpregabalin stereoisomers using a Michael addition of dimethyl malonate to a racemic nitroalkene. The key step of the synthesis operates as a kinetic resolution with a chiral squaramide
  • catalyst. Furthermore, specific organocatalysts can provide respective stereoisomers of the key Michael adduct in up to 99:1 er. Keywords: kinetic resolution; Michael addition; organocatalysis; pregabalin; squaramide; Introduction Asymmetric organocatalysis has considerably broadened possibilities for
  • addition of dimethyl malonate. An initial catalyst screening was performed in dichloromethane, based on our previous experiences with this type of Michael additions [18]. We have employed a range of squaramide and thiourea organocatalysts C1–C7 [18][27][28][29][30][31][32][33][34], as well as two newly
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Published 05 Mar 2018

Novel amide-functionalized chloramphenicol base bifunctional organocatalysts for enantioselective alcoholysis of meso-cyclic anhydrides

  • Lingjun Xu,
  • Shuwen Han,
  • Linjie Yan,
  • Haifeng Wang,
  • Haihui Peng and
  • Fener Chen

Beilstein J. Org. Chem. 2018, 14, 309–317, doi:10.3762/bjoc.14.19

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  • development of chiral bifunctional urea 1 [35], thiourea 2 and 3 [36][37], sulfonamide 4 [38][39][40] and squaramide 5 [38][39][40] catalysts derived from chloramphenicol base (Figure 1), which showed excellent reactivity and enantioselectivity for this asymmetric transformation. A typical example of the
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Published 31 Jan 2018

Chiral phase-transfer catalysis in the asymmetric α-heterofunctionalization of prochiral nucleophiles

  • Johannes Schörgenhumer,
  • Maximilian Tiffner and
  • Mario Waser

Beilstein J. Org. Chem. 2017, 13, 1753–1769, doi:10.3762/bjoc.13.170

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  • the first squaramide-containing chiral PTCs E, which also turned out to be very promising catalysts for the asymmetric α-fluorination of compounds 1 [44]. The groups of Ma and Cahard have intensively investigated the use of chiral spirocyclic phosphonium salts F as phase-transfer catalysts for
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Published 22 Aug 2017
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