Copper catalysis with redox-active ligands

• Agnideep Das,
• Yufeng Ren,
• Cheriehan Hessin and
• Marine Desage-El Murr

Beilstein J. Org. Chem. 2020, 16, 858–870, doi:10.3762/bjoc.16.77

• ). Acetonitrile gave the highest yield (55%) and ee (72%) of product (S)-11 in presence of Λ-10 as catalyst. While the free ligand is found to catalyze the reaction, the authors show that the templating effect of the copper ion is necessary to sustain enantioselectivity. Himmel and co-workers have reported the

Combining enyne metathesis with long-established organic transformations: a powerful strategy for the sustainable synthesis of bioactive molecules

• Valerian Dragutan,
• Ileana Dragutan,
• Albert Demonceau and
• Lionel Delaude

Beilstein J. Org. Chem. 2020, 16, 738–755, doi:10.3762/bjoc.16.68

• constructing the five-membered oxacyclic ring. As stated in this protocol, a functionalized enyne precursor was prepared in several steps with high enantioselectivity (92% ee), starting from isovanillin. This precursor underwent a ring-closing metathesis in the presence of the Grubbs first-generation Ru

Recent advances in Cu-catalyzed C(sp³)–Si and C(sp³)–B bond formation

• Balaram S. Takale,
• Ruchita R. Thakore,
• Elham Etemadi-Davan and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2020, 16, 691–737, doi:10.3762/bjoc.16.67

• PhMe2Si moiety in a 1,4-manner to unsaturated nitro and cyano derivatives leading to adducts 209–218, each being obtained in high chemical yield and good enantioselectivity (Scheme 37). 1.5 Miscellaneous reactions The Tsuji group developed a mild method for the regio-divergent silacarboxylation of allenes

• enantioselectivities remain unaffected. In addition to the impact of steric effects, variations in the alkyl-substituted silicon reagents also negatively impacted the chemical yields. However, again, there was no effect on enantioselectivity. Interestingly, upon replacement of the alkyl groups on the silicon by three

• )- and (E)-alkenes 311 afforded the (E)-alkene 312 as the major product. The targeted γ-borylated compounds (relative to the leaving group) were formed, each with high enantioselectivity, which can be used for further stereoselective C–C and C–X (X = heteroatom) bond formation. Catalytic Cu(NHC)-mediated

Asymmetric synthesis of CF₂-functionalized aziridines by combined strong Brønsted acid catalysis

• Xing-Fa Tan,
• Fa-Guang Zhang and
• Jun-An Ma

Beilstein J. Org. Chem. 2020, 16, 638–644, doi:10.3762/bjoc.16.60

• no enantioselectivity at all. As arylboronic acids have been harnessed to enhance the Brønsted acidity in asymmetric organocatalysis in combination with chiral diols or chiral aminoalcohols [40][41][42][43][44], we envisioned that the simultaneous use of arylboronic acids and chiral Brønsted acids

• the chiral additive in combination with 2-carboxyphenylboronic acid (COOH-BA) in the model reaction (Table 1, entries 3–8). We were pleased to find that CDSI-4 gave the most promising result in terms of both yield and enantioselectivity (64% isolated yield with 73% ee, Table 1, entry 6). An

• to further improve the enantioselectivity promoted us to search for other practical solutions. Considering the poor solubility of 4a in organic solvents, a dissolution–filtration process with isopropanol was found to be workable for increasing the final ee value. This simple procedure could afford 4a

Copper-catalyzed enantioselective conjugate reduction of α,β-unsaturated esters with chiral phenol–carbene ligands

• Shohei Mimura,
• Sho Mizushima,
• Yohei Shimizu and
• Masaya Sawamura

Beilstein J. Org. Chem. 2020, 16, 537–543, doi:10.3762/bjoc.16.50

• diethoxymethylsilane (4 equiv) as a reductant and t-AmOH (1 equiv) as a protonation reagent in DMA as the solvent at 25 °C for 15 h, the product 2a was produced in 98% yield (1H NMR analysis) with a promising enantioselectivity of 69% ee (Table 1, entry 1). When the phenolic hydroxy group of L1 was changed to a

• methoxy group (in L2), the enantioselectivity drastically dropped to −10% ee, while the yield remained 99% (Table 1, entry 2). Similarly, N,N'-dimesityl-NHC L3, which lacked an oxygen functionality in the N-aryl group, showed poor enantioselectivity (9% ee) with high yield (99% yield, Table 1, entry 3

• ). Thus, the hydroxy group of L1 was essential for the enantioselectivity by the catalyst. When the mesityl group of L1 was changed to a bulkier 2-Me-4,6-Cy2-C6H2 group in L4, the enantioselectivity was markedly improved to 90% ee, with a high yield (97%, Table 1, entry 4). A naphthol substituent on the

Architecture and synthesis of P,N-heterocyclic phosphine ligands

• Wisdom A. Munzeiwa,
• Bernard Omondi and
• Vincent O. Nyamori

Beilstein J. Org. Chem. 2020, 16, 362–383, doi:10.3762/bjoc.16.35

• catalysis [116]. However, the majority of them exhibited good to moderate enantioselectivity. The syntheses of chiral phosphinooxazolines was reported independently by Williams et al., Pfaltz and Helmchen, and Matt and Pfaltz [48][116][117]. Pfaltz et al. reported on the postfunctionalization in the

Copper-catalyzed enantioselective conjugate addition of organometallic reagents to challenging Michael acceptors

• Delphine Pichon,
• Jennifer Morvan,
• Christophe Crévisy and
• Marc Mauduit

Beilstein J. Org. Chem. 2020, 16, 212–232, doi:10.3762/bjoc.16.24

• reagents to these challenging Michael acceptors, with excellent regio- and enantioselectivity. Furthermore, thanks to their easy derivatization, the resulting chiral conjugated products could be converted into various natural products. The aim of this tutorial review is to summarize recent advances

• moderate to good yields, with ee values of up to 76%. When the conjugate addition was performed with Grignard reagents, significant amounts of 1,2-products and enols were formed, despite the use of cryogenic conditions. (R)-BINAP (L2) gave the best regio- and enantioselectivity, with 62% of the 1,4-product

• combination with (R)-TolBINAP (L3), a promising 85% regioselectivity was observed, without altering the enantioselectivity (90% ee), whereas only 32% of the desired 1,4- product was obtained without TMSCl [20]. With those optimized conditions, various enals and Grignard reagents were screened. Nevertheless

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

• Bratislava, Mlynská dolina, Ilkovičova 6, 84215 Bratislava, Slovakia 10.3762/bjoc.15.290 Abstract A range of chiral hydrogen-bond-donating organocatalysts was tested in the Ireland–Claisen rearrangement of silyl ketene acetals. None of these organocatalysts was able to impart any enantioselectivity on the

• diastereoselectivities, and ees up to 86% [26]. Rearrangement of allyl esters of glycine derivatives gave under similar conditions amino acids with a quaternary stereocenter on the β-carbon with high yields and excellent diastereo- as well as enantioselectivity [5]. A reductive rearrangement of allyl esters of acrylic

• activate the enolates or the corresponding silyl ketene acetals or stabilize the corresponding transition states. In addition, chiral organocatalysts could induce diastereo- as well as enantioselectivity. Therefore, we examined the Ireland–Claisen rearrangement of ester 1c in the presence of a range of

A review of asymmetric synthetic organic electrochemistry and electrocatalysis: concepts, applications, recent developments and future directions

• Munmun Ghosh,
• Valmik S. Shinde and
• Magnus Rueping

Beilstein J. Org. Chem. 2019, 15, 2710–2746, doi:10.3762/bjoc.15.264

• . Notably, the highest optical yields were achieved using strychnine (Scheme 8) [31]. Similarly, by applying modified electrolytic conditions, in 1993, Schoo and Schäfer increased the enantioselectivity of the alkaloid-catalyzed enantioselective electroreduction of 4-methylcoumarin (8) relative to that

• of methyl-substituted diols 51 on a TEMPO-modified graphite felt electrode in the presence of the chiral base (−)-sparteine (43) with excellent enantioselectivity (conditions A, Scheme 20) [51]. Later in 2003, they reported another protocol for a graphite felt electrode for asymmetric electrochemical

• supporting electrolyte. A slight improvement in the enantioselectivity (8.4% ee) was observed using 55b [55]. Kodama explained the reason of chiral induction in terms of ion pair interaction [56]. A further improvement in stereoselectivity was reported by Yadav, who added tetrabutylammonium trifluoroborate

Synthesis of acremines A, B and F and studies on the bisacremines

• Nils Winter and
• Dirk Trauner

Beilstein J. Org. Chem. 2019, 15, 2271–2276, doi:10.3762/bjoc.15.219

• reduction conditions to afford cyclohexa-1,4-diene 13 [9]. Enantioselective Sharpless dihydroxylation proceeded in good chemoselectivity but with modest yield and optical purity (25% ee). Unfortunately, all attempts to improve the enantioselectivity of this reaction failed. We discovered, however, that at a

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

• conditions with excellent enantioselectivity and yields, a broad substrate scope, as well as a wide range of functional group compatibility. Notably, this strategy overcomes the challenges associated with the formation of secondary allylic fluorides bearing α-linear substituents, providing complete regio and

• were thus obtained with good enantioselectivity. In the same year, Kim’s group [97] accomplished an efficient enantioselective electrophilic α-fluorination of various α-chloro-β-ketoesters catalyzed by chiral nickel complexes with good enantioselectivity (up to 99% ee). Notably, the chiral nickel

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

• reaction with the highest enantioselectivity. The importance of the bifunctional system for the catalytic activity and enantioselectivity was demonstrated by performing a series of reactions with lower activity and selectivity, utilizing free-base porphyrin 16h with triazolium moieties and the two

• component catalytic system composed of 16c before methylation and TBAI as reference catalysts. Optimization studies of the reaction conditions showed that the addition of CHCl3 and lowering of the reaction temperature (to 10 °C) considerably increased the enantioselectivity (s value of 4.1). An evaluation

α-Photooxygenation of chiral aldehydes with singlet oxygen

• Dominika J. Walaszek,
• Magdalena Jawiczuk,
• Jakub Durka,
• Olga Drapała and
• Dorota Gryko

Beilstein J. Org. Chem. 2019, 15, 2076–2084, doi:10.3762/bjoc.15.205

• )-18 furnished, after in situ reduction, diol (2R,3R)-6 with high syn-diastereo- and enantioselectivity (Scheme 6). Conclusion We have demonstrated that oxygenation of aldehydes with singlet oxygen can be successfully achieved in the presence of diphenylprolinol silyl ether affording diols in a highly

Naphthalene diimides with improved solubility for visible light photoredox catalysis

• Barbara Reiß and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2019, 15, 2043–2051, doi:10.3762/bjoc.15.201

• ) is one of the benchmark reactions for photoredox catalysis because it combines photoredox catalysis with organocatalysis [53]. Initially, [Ru(bpy)3]Cl2 was applied by MacMillan et al. as photoredox catalyst together with the chiral imidazolidinone 15 as organocatalyst to achieve enantioselectivity

• following paragraphs because enantioselectivity is not a matter of discussion in this work. The photoredox catalysis with NDI 1 was performed by LEDs with 387 nm maximum emission wavelength and an irradiation time of 18 h. In order to ensure solubility of all components, a solvent mixture of DMF/CH2Cl2 = 1

Complexation of chiral amines by resorcin[4]arene sulfonic acids in polar media – circular dichroism and diffusion studies of chirality transfer and solvent dependence

• Bartosz Setner and
• Agnieszka Szumna

Beilstein J. Org. Chem. 2019, 15, 1913–1924, doi:10.3762/bjoc.15.187

• cyclodextrines, which, when unmodified, interact with a wide range of hydrophobic guests albeit with low general selectivity and enantioselectivity in particular [6]. In this paper we present a group of synthetic macrocyclic compounds – resorcin[4]arene sulfonic acids (RSAs) and analyze their interactions with

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

• , recyclable catalyst in the N-arylation of indoles [45][46]. Copper catalysts have shown exceptional enantioselectivity for reactions such as hydrosilylation, hydroboration, and heterogeneous as well as homogeneous hydrogenation [47][48][49]. Also, the copper salts found used as oxidants in a number of

Enantioselective PCCP Brønsted acid-catalyzed aza-Piancatelli rearrangement

• Gabrielle R. Hammersley,
• Meghan F. Nichol,
• Helena C. Steffens,
• Jose M. Delgado,
• Gesine K. Veits and
• Javier Read de Alaniz

Beilstein J. Org. Chem. 2019, 15, 1569–1574, doi:10.3762/bjoc.15.160

• , it was not until 2016 that the first asymmetric aza-Piancatelli reaction was described. To control the absolute stereochemistry of the aza-Piancatelli rearrangement, Rueping [35], Sun [36], and Patil [37] independently demonstrated that chiral phosphoric acids can be used as an enantioselectivity

• optimization of the reaction conditions was required to achieve high enantioselectivity and good yield, with small variations to the catalyst architecture or solvent having dramatic effects on enantioselectivity or yield. Because of these challenges and our group’s ongoing interest in further developing the

• reaction of the furylcarbinol to generate the oxocarbenium intermediate. Second, by analogy to asymmetric induction in aza-Piancatelli reactions with chiral phosphoric acids, where enantioselectivity has generally been achieved by strategically installing bulky groups on the hydrogen-bonding catalysts, we

Enantioselective Diels–Alder reaction of anthracene by chiral tritylium catalysis

• Qichao Zhang,
• Jian Lv and
• Sanzhong Luo

Beilstein J. Org. Chem. 2019, 15, 1304–1312, doi:10.3762/bjoc.15.129

• , the enantioselectivity was low in most cases. In addition, the synthetic efforts to access these chiral cations were generally non-trivial which limited their further development. Recently, we developed a chiral ion-pair strategy for asymmetric carbocation catalysis, with chiral trityl phosphate as

• cycloadduct 5a in excellent enantioselectivity (97% ee), however, with only 9% yield (Table 1, entry 1). Subsequent efforts to improve the activity by enhancing the dissociation efficiency of latent carbocation through heating or photolysis did not lead to any improvement. We next investigated whether the

• anthracene (3a) and β,γ-unsaturated α-ketoester 4a. When TP was first treated with metal Lewis acid (Scheme 2a, and Table S1 in Supporting Information File 1), the reaction showed good reactivity but no enantioselectivity at all, indicating a strong background reaction (Table 1, entry 2). We next examined

Synthesis of non-racemic 4-nitro-2-sulfonylbutan-1-ones via Ni(II)-catalyzed asymmetric Michael reaction of β-ketosulfones

• Alexander N. Reznikov,
• Anastasiya E. Sibiryakova,
• Marat R. Baimuratov,
• Eugene V. Golovin,
• Victor B. Rybakov and
• Yuri N. Klimochkin

Beilstein J. Org. Chem. 2019, 15, 1289–1297, doi:10.3762/bjoc.15.127

• nitroalkenes in the presence of Ni(II) complexes with various chiral vicinal diamines was studied. This reaction provides convenient access to non-racemic 4-nitro-2-sulfonylbutan-1-ones with two stereocenters with high yield and excellent enantioselectivity (up to 99%). It has been established that the

• , which allows to obtain chiral cyclic sulfones with high enantioselectivity [10][11][12]. Also non-racemic cyclic sulfones can be obtained by the Diels–Alder reaction, catalyzed by chiral Lewis acids or organocatalysts. Rh- and Cu-catalyzed CH-insertion reactions occurring at moderate or high

• enantioselectivity are also known [13][14][15][16][17][18]. The studied methods for obtaining acyclic sulfones with stereogenic centers in the side chain are more limited. One of the most significant approaches to obtaining both cyclic and acyclic chiral sulfones is asymmetric hydrogenation in the presence of

Ugi reaction-derived prolyl peptide catalysts grafted on the renewable polymer polyfurfuryl alcohol for applications in heterogeneous enamine catalysis

• Alexander F. de la Torre,
• Gabriel S. Scatena,
• Oscar Valdés,
• Daniel G. Rivera and
• Márcio W. Paixão

Beilstein J. Org. Chem. 2019, 15, 1210–1216, doi:10.3762/bjoc.15.118

• polyfurfuryl alcohol-supported catalysts for applications in heterogeneous enamine catalysis. The utilization of the polymer-supported catalysts in both batch and continuous-flow organocatalytic procedures proved moderate catalytic efficacy and enantioselectivity, but excellent diastereoselectivity in the

• diastereoselectivity remains constantly high in all solvents [19]. Unfortunately, the enantioselectivity of the Michael additions remained moderate with both catalysts in all tested solvents and conditions, only rising to 84% ee when using catalyst 3 in toluene. The reason of the better catalytic performance of PFA

• material by β-nitrostyrene (50 times as residence time calculated) limits the formation of the Michael product and, consequently, lowers the chemical efficiency. Despite the good level of diastereocontrol in Michael addition (dr 95:5 syn/anti), a little drop in the enantioselectivity was observed (i.e., 74

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

• rearrangement that would lead to isoindolinone 46 through the bridged intermediate 51. Therefore, this mechanistic path shows that the enantioselectivity of the reaction is a consequence of a dynamic kinetic resolution of enamine 50. Cyanide can also be used, instead of isocyanide, in an analogous three

Novel (2-amino-4-arylimidazolyl)propanoic acids and pyrrolo[1,2-c]imidazoles via the domino reactions of 2-amino-4-arylimidazoles with carbonyl and methylene active compounds

• Victoria V. Lipson,
• Tetiana L. Pavlovska,
• Nataliya V. Svetlichnaya,
• Anna A. Poryvai,
• Nikolay Yu. Gorobets,
• Erik V. Van der Eycken,
• Irina S. Konovalova,
• Svetlana V. Shiskina,
• Alexander V. Borisov,
• Vladimir I. Musatov and
• Alexander V. Mazepa

Beilstein J. Org. Chem. 2019, 15, 1032–1045, doi:10.3762/bjoc.15.101

• described in the literature [38][39][40], the authors recognized the importance of protecting the amide fragment of isatin, since it affects the reactivity and, in some cases, the enantioselectivity of processes. In order to prevent undesirable side reactions in the future, three-component condensations

Catalytic asymmetric oxo-Diels–Alder reactions with chiral atropisomeric biphenyl diols

• Chi-Tung Yeung,
• Wesley Ting Kwok Chan,
• Wai-Sum Lo,
• Ga-Lai Law and
• Wing-Tak Wong

Beilstein J. Org. Chem. 2019, 15, 955–962, doi:10.3762/bjoc.15.92

• , different from the synthesis of catalyst 3, asymmetric reduction of the corresponding ketone, (2-bromophenyl)(mesityl)methanone c, using (S)-(–)-2-methyl-CBS-oxazaborolidine as the catalyst resulted in a very low enantioselectivity (<15% ee) of the product, (2-bromophenyl)(mesityl)methanol (d, Scheme 3

• removing the chiral-resolving menthyl substituent with lithium aluminium hydride (LAH), the enantioselectivity of (R)-d was higher than 99% ee when checked with HPLC (Supporting Information File 1, Figure S3). Catalyst 4 was then obtained by homo-coupling of (R)-d with Ni(PPh3)3Br2/Zn with 37% yield. The

• previously to have a significant effect on controlling catalytic enantioselectivites [41][42]. For organocatalyst 6, it gave the highest enantioselectivity (59% ee) but a low chemical yield. When the bulkier trimethylacetaldehyde was used as substrate, the enantioselectivities were improved when 1–3 were

New α- and β-cyclodextrin derivatives with cinchona alkaloids used in asymmetric organocatalytic reactions

• Iveta Chena Tichá,
• Simona Hybelbauerová and
• Jindřich Jindřich

Beilstein J. Org. Chem. 2019, 15, 830–839, doi:10.3762/bjoc.15.80

• improve the rate and modulate the regioselectivity and enantioselectivity of reactions [11]. For example, metal-based CD catalytic systems and CD derivatives for organocatalysis have already shown promising results in the studies by Hapiot and Monflier [12], Armspach [13] and others [14][15]. The chemical

• lower enantiomeric excess (54% ee). Conversely, Shen et al. [18] performed an aldol reaction in a buffer using L- and D-proline-derived CDs connected through a pyrrolidine skeleton as catalysts and observed 94% ee. More recently, Liu et al. [19] reported the excellent enantioselectivity of 99% ee in an

Diastereo- and enantioselective preparation of cyclopropanol derivatives

• Marwan Simaan and
• Ilan Marek

Beilstein J. Org. Chem. 2019, 15, 752–760, doi:10.3762/bjoc.15.71

• facial selection by the catalyst is required: (i) regioselectivity when R1 is different to H and enantioselectivity when R1 is equal to H (left or right) and (ii) diastereotopic face selection (top or bottom) as described in Scheme 2. Since the pioneering addition of a carbon–metal bond (carbometalation