Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

Hierarchically assembled helicates as reaction platform – from stoichiometric Diels–Alder reactions to enamine catalysis

• David Van Craen,
• Jenny Begall,
• Johannes Großkurth,
• Leonard Himmel,
• Oliver Linnenberg,
• Elisabeth Isaak and
• Markus Albrecht

Beilstein J. Org. Chem. 2020, 16, 2338–2345, doi:10.3762/bjoc.16.195

• reaction yielded the racemic product after purification. Scheme 3 is showing that the induction of stereochemistry of the Diels–Alder reaction depends on the chirality at the chiral ligand and not at the helix. This allows improvement of the stereoselectivity by using more appropriate sterically hindered

Design and synthesis of a bis-macrocyclic host and guests as building blocks for small molecular knots

• Elizabeth A. Margolis,
• Rebecca J. Keyes,
• Stephen D. Lockey IV and
• Edward E. Fenlon

Beilstein J. Org. Chem. 2020, 16, 2314–2321, doi:10.3762/bjoc.16.192

• were formed (see Scheme S1 in Supporting Information File 1). Repeated attempts to grow X-ray crystals of the product failed. To test for topological chirality, a europium chiral shift reagent was added, but the 1H NMR spectrum was too noisy to discern any peak doubling. Additional experiments, such as

Synthetic approaches to bowl-shaped π-conjugated sumanene and its congeners

• Shakeel Alvi and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 2212–2259, doi:10.3762/bjoc.16.186

• et al. [13], this field of research is continuously booming because of the developments of advanced synthetic organic tools [14][15][16]. Among the PAHs, the buckybowls are of significant importance not only because of the presence of unique inherent chirality (bowl-chirality) originating either from

• strategy via the transfer of sp3 chirality of 27 into the bowl chirality of 28 as a key conversion (Scheme 3) [17][31]. In this context, they began with the Pd-catalyzed hydrosilylation reaction using HSiCl3 at −3 °C in the presence of a chiral phosphine ligand to furnish the hydrosilylated product which

Naphthalene diimide–amino acid conjugates as novel fluorimetric and CD probes for differentiation between ds-DNA and ds-RNA

• Annike Weißenstein,
• Myroslav O. Vysotsky,
• Ivo Piantanida and
• Frank Würthner

Beilstein J. Org. Chem. 2020, 16, 2032–2045, doi:10.3762/bjoc.16.170

• molecules [49][50]. Also achiral small molecules can eventually acquire induced CD (ICD) upon binding to chiral polynucleotides, which could give useful information about modes of interaction [49][50]. The NDIs 3a,b are chiral but the chirality of the amino acid residue is not transferred through the

• commonly attributed to nucleobase pairs. However, since it is not likely that the chirality of the double helix will strongly increase upon binding of a small molecule, the most prominent changes at 300 nm and above are most likely attributable to ICD bands of the NDI core bound to the polynucleotide in a

[3 + 2] Cycloaddition with photogenerated azomethine ylides in β-cyclodextrin

• Margareta Sohora,
• Leo Mandić and
• Nikola Basarić

Beilstein J. Org. Chem. 2020, 16, 1296–1304, doi:10.3762/bjoc.16.110

• the macrocyclic host affected the stereochemistry of the reaction. Moreover, we studied photodecarboxylation reactions initiated by the phthalimide chromophore [17][18][19] and applied them in cyclizations with memory of chirality [20] and diastereoselective peptide cyclizations [21

A cyclopeptide and three oligomycin-class polyketides produced by an underexplored actinomycete of the genus Pseudosporangium

• Shun Saito,
• Kota Atsumi,
• Tao Zhou,
• Keisuke Fukaya,
• Daisuke Urabe,
• Naoya Oku,
• Md. Rokon Ul Karim,
• Hisayuki Komaki and
• Yasuhiro Igarashi

Beilstein J. Org. Chem. 2020, 16, 1100–1110, doi:10.3762/bjoc.16.97

• -acetyl-ʟ-Tyr-ʟ-Pro-ʟ-Trp, was determined by a combination of spectroscopic analyses, chemical derivatization, ECD calculation, and DFT-based theoretical chemical shift calculation, revealing the presence of an (Sa)-axial chirality around the biaryl bond. Compounds 2–4 lacked hydroxylation on the side

• Pro residues was not proven by HMBC, but confirmed by ROESY correlations between H-5' and H-2/H-3 to give a planar structure of 1. The chirality of the Pro residue was determined by the advanced Marfey’s method. Compound 1 was acid-hydrolyzed and the hydrolysate was derivatized with 1-fluoro-2,4

• C2''. As positive ΔδS−R values were obtained for 10''-NH and H-11'', and negative values for 2''-NH, H-2', H-3', H-4', H-5', and 2-NH (Figure 3), an (S)-configuration was assigned to C-2''. The chirality of the AcTyr residue was investigated by computer-assisted conformational analysis and NMR

Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches

• Rodrigo Costa e Silva,
• Luely Oliveira da Silva,
• Aloisio de Andrade Bartolomeu,
• Timothy John Brocksom and
• Kleber Thiago de Oliveira

Beilstein J. Org. Chem. 2020, 16, 917–955, doi:10.3762/bjoc.16.83

• amides (71–99% yields) and with 5–66% ee (Scheme 42). In 2018, Meng and co-workers developed a bifunctional photo-organocatalyst combining both the photosensitizer and the chirality inducer. Relevant enantiomeric excesses were observed (up to 86% ee) in the oxidation of both β-keto esters and β-keto

Bipyrrole boomerangs via Pd-mediated tandem cyclization–oxygenation. Controlling reaction selectivity and electronic properties

• Liliia Moshniaha,
• Marika Żyła-Karwowska,
• Joanna Cybińska,
• Piotr J. Chmielewski,
• Ludovic Favereau and
• Marcin Stępień

Beilstein J. Org. Chem. 2020, 16, 895–903, doi:10.3762/bjoc.16.81

• each produced a single broadened signal, indicating that the helix inversion occurs in the fast exchange regime. This apparently faster inversion in cNMI2H than in the cNMI2O and cNDA2O lactams correlates with the higher bond order of the α–α linkage in the latter two systems. The chirality of cNMI3H

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

• iminosemiquinone redox-active ligand which was oxidized to iminobenzoquinone. The Canary group [30] reported a redox-reconfigurable copper catalyst that exhibits reversal of its helical chirality through redox stimuli (Scheme 8). Combining ʟ-methionine and catalytic urea groups with two different copper salts as

• precursors affords both enantiomers Δ-10 (from CuClO4) and Λ-10 from (Cu(CH3CN)4PF6). UV–vis and circular dichroism spectroscopic studies evidence that the helical chirality exhibited by these two catalysts could be reversed by redox stimuli. These complexes could perform enantioselective Michael addition

• trifluoromethylation of heteroaromatics with redox-active iminosemiquinone ligands. Reversal of helical chirality upon redox stimuli and enantioselective Michael addition with a redox-reconfigurable copper catalyst. Interaction of guanidine-copper catalyst with oxygen and representative coupling products. a4 mol

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

• ]. Following this report, Oestreich and co-workers examined asymmetric additions of silicon to unsaturated ketones 113 using P–N-type ligand L13. However, the background reaction of the silyl–zinc reagent was predominant leading to poor chirality transfer from the phosphine ligand L13, giving essentially the

Synthesis of C₇₀-fragment buckybowls bearing alkoxy substituents

• Yumi Yakiyama,
• Shota Hishikawa and
• Hidehiro Sakurai

Beilstein J. Org. Chem. 2020, 16, 681–690, doi:10.3762/bjoc.16.66

• vapour diffusion method using CHCl3/hexane conditions. Figure 2 shows the crystal structure of 5a. The crystal was obtained as a racemic compound containing a pair of two enantiomers defined by bowl chirality [26], as a result of the rapid bowl inversion under the crystallization conditions. 5a formed a

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

• phosphorous atom, and the ease of optimizing steric and electronic properties. Additionally, properties like chirality can be conferred to the backbone of the ligands to generate C-stereogenic [1] and P-chirogenic [2] compounds. Furthermore, the 31P-nucleus abundance allows the use of NMR for reaction

• -oxazaphosphorine ligands with a P-center and backbone chirality (Scheme 24). Spiro-1,3-amino alcohol compounds 124 were synthesized according to a literature procedure [107]. For the synthesis of the mono-N-methylated amino alcohol ligands a cooled solution of dichlorophenylphosphine was treated with triethylamine

[1,3]/[1,4]-Sulfur atom migration in β-hydroxyalkylphosphine sulfides

• Katarzyna Włodarczyk,
• Piotr Borowski and
• Marek Stankevič

Beilstein J. Org. Chem. 2020, 16, 88–105, doi:10.3762/bjoc.16.11

• at the γ-carbon atom, suggesting that the reaction followed a more complex mechanism. All reactions tested proceeded with the formation of an additional chirality center at the γ-carbon atom in the alkyl substituent, and therefore, almost all products were obtained as mixtures of epimers

• ]-rearrangement proceeded with additional partial enrichment of one enantiomer. The latter may have occurred through the preferential acylation of one of two diastereoisomers under the reaction conditions where the second chirality center at the phosphorus atom influenced the ratio of the acylation reaction. With

• . The nature of this difference is currently a subject of further research in our laboratory. Nevertheless, the above results opened a new pathway for the synthesis of bicyclic organophosphorus compounds possessing a chirality center at phosphorus. Moreover, the formation of the bicyclic compounds

Pigmentosins from Gibellula sp. as antibiofilm agents and a new glycosylated asperfuran from Cordyceps javanica

• Soleiman E. Helaly,
• Wilawan Kuephadungphan,
• Patima Phainuphong,
• Mahmoud A. A. Ibrahim,
• Kanoksri Tasanathai,
• Suchada Mongkolsamrit,
• Janet Jennifer Luangsa-ard,
• Souwalak Phongpaichit,
• Vatcharin Rukachaisirikul and
• Marc Stadler

Beilstein J. Org. Chem. 2019, 15, 2968–2981, doi:10.3762/bjoc.15.293

• with pigmentosin A, a 3,4-dihydro-α-naphthopyrone dimer with a 7,7′-dimethoxy pattern, by comparing its spectroscopic data with the published data for pigmentosin A [12]. Nevertheless, the chirality of the stereogenic centers C-3/C-3′ as well as the atropisomerism at the 6,6′ axis of pigmentosin A (1

• effects: a first negative at 274 nm (Δε −196) and a positive second one at 252 nm (Δε +203), indicating the helicity of the 6-6′ axis as aR, according to the exciton chirality method [13]. Furthermore, the TDDFT-ECD calculations were performed on three isomers, namely (3R,3′R,6R)-1, (3S,3′S,6S)-1, and (3S

• -13′, H-3′, and H2-4′ (+0.06, +0.24, and +0.10, respectively). Thus, the absolute configuration at C-12′ was assigned as R (Figure 3). The atropisomerism at the 6,6′ axis of pigmentosin B (2) was assigned, similarly to pigmentosin A (1), by the exciton chirality method. A strong negative first Cotton

Influence of the cis/trans configuration on the supramolecular aggregation of aryltriazoles

• Sara Tejera,
• Giada Caniglia,
• Rosa L. Dorta,
• Andrea Favero,
• Javier González-Platas and
• Jesús T. Vázquez

Beilstein J. Org. Chem. 2019, 15, 2881–2888, doi:10.3762/bjoc.15.282

• ECD exciton chirality method [22][23][24]. ECD of compound 10 in a DMSO/H2O (1:2, v/v) solution and in gel form were successfully measured (Figure 6). ECD of the solution exhibited negative first/positive second exciton Cotton effects at 262 (Δε = −8.6) and 242 nm (Δε = +3.3), respectively (Figure 6

A chiral self-sorting photoresponsive coordination cage based on overcrowded alkenes

• Constantin Stuckhardt,
• Diederik Roke,
• Wojciech Danowski,
• Edwin Otten,
• Sander J. Wezenberg and
• Ben L. Feringa

Beilstein J. Org. Chem. 2019, 15, 2767–2773, doi:10.3762/bjoc.15.268

• switches have not been reported in the literature. In chiral self-sorting SCCs, either homo- or heterochiral complexes are formed exclusively through high fidelity recognition of the components within the complex [31][32][33]. The formation of such complexes with high selectivity and well-defined chirality

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

• exploiting electroorganic reactions to their fullest extent [15]. Asymmetric electrochemical synthesis refers to electroorganic reactions resulting in the introduction of one or more new elements of chirality into a target compound. The induction of asymmetry into achiral substrates through electrochemical

• asymmetric electrocatalytic reactions. Review Classification and systematic description of chiral inductors Transformations of achiral organic substrates into chiral products by electrochemical synthetic methods require the active participation of an external source of chirality. Organic chemists working in

• summarized the background and recent advances and arranged this article to provide a systematic description of electrochemical reactions in which chirality has been induced using these three sources (Figure 1). Chemically modified chiral electrodes Electrochemical asymmetric reductions using chiral

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

• compounds transparent in the UV–vis region. In solution, chirality of diols is transfered to the newly in situ-formed complexes. The signs of Cotton effects (CEs) observed in their spectra undergo the helicity rule linking the positive/negative sign of CE at about 300–400 nm with positive/negative sign of O

Attempted synthesis of a meta-metalated calix[4]arene

• Christopher D. Jurisch and
• Gareth E. Arnott

Beilstein J. Org. Chem. 2019, 15, 1996–2002, doi:10.3762/bjoc.15.195

• yielding transformations to azide and 1,2,3-triazole derivatives which may have application in other areas of research. Keywords: calixarene; inherent chirality; mesoionic carbene; mononitration; ruthenacycle; Introduction Calix[4]arenes are a class of diverse macrocyclic compounds which have been the

• whose chiral nature is a result of selective substitution on the calix[4]arene by various functional groups [9]. In particular, we have focused on the less-studied meta-substituted derivatives [10] whose inherent chirality is more commonly introduced by a suitable directing group [11][12][13][14][15

• potential implications for asymmetric catalysis, due to the inherent chirality of the calix[4]arene, coupled with the point chirality from, for example, a tetrahedral ruthenium center. We therefore decided to apply the methods reported by Albrecht to a calix[4]arene system in order to prove this theory

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

• spectroscopy. Chirality transfer from amines onto a resorcinarene skeleton was manifested by the appearance of signals in CD spectra and diastereotopic splitting in NMR spectra. The complexes proved to be thermodynamically stable in methanol, but DMSO and methanol/water mixtures were found to be highly

• disintegrative for these complexes. This result is quite non-intuitive and worth attention in the context of formation of supramolecular complexes in polar environment, for which DMSO is most often a first-choice solvent. Keywords: cavitands; chirality; macrocycle; resorcin[4]arene; self-assembly

• manifested in chirality transfer. We will also present a crucial and non-intuitive solvent dependence. RSAs (e.g., 1) can be considered as analogues of calix[4]arene sulfonic acids (CSAs) – the class of macrocycles widely studied in the context of various host–guest interactions, especially with various

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

• MeBmt are rather challenging endeavor since these amino acids in addition to an E-configured C=C bond has three neighboring stereogenic centers. The starting aziridine aldehyde (2R,1'R)-6 already introduces the required configuration at C2 and the two other centers of chirality were created by the

Synthesis, enantioseparation and photophysical properties of planar-chiral pillar[5]arene derivatives bearing fluorophore fragments

• Guojuan Li,
• Chunying Fan,
• Guo Cheng,
• Wanhua Wu and
• Cheng Yang

Beilstein J. Org. Chem. 2019, 15, 1601–1611, doi:10.3762/bjoc.15.164

• : aggregation; circular dichroism; chirality; click chemistry; macrocycles; pillar[5]arenes; Introduction Planar-chiral compounds are structurally appealing and potentially applicable in various functional materials such as chiral discriminators [1][2], chiral polymers, supramolecular sensors [3] and chiral

• that differs from the common macrocycles is the planar chirality resulting from the different orientations of the alkoxy substituents on the rims. Theoretically, eight conformers can be formed including diastereomeric ones: (Sp,Sp,Sp,Sp,Sp), (Rp,Sp,Sp,Sp,Sp), (Rp,Rp,Sp,Sp,Sp), (Rp,Sp,Rp,Sp,Sp) and

• center and therefore chirality transfer is non-effective [43]. Supramolecular assembly usually leads to different photophysical properties than homogeneous solutions. We have demonstrated that solvents play a critical role in chiral recognition and chiral photoreactions [44][45][46][47][48][49][50][51

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

• synthesize stabilized chiral carbocations with chirality installed onto their backbones. Pioneering efforts along this line by Kagan, Sammakia, and Chen have shown that chiral catalysis with such chiral carbocations was indeed plausible to achieve stereocontrol (Scheme 1a). [14][15][16][17][18][19]. However

• is catalyzed by tritylium salts with Fe(III)-complexed bisphosphate as the chirality-inducing anion. With the optimal reactions conditions established, the scope was next explored with Ph3CCl/2f in CH2Cl2 (DCM) at room temperature and the results are presented in Table 2. A variety of β,γ-unsaturated

Steroid diversification by multicomponent reactions

• Leslie Reguera,
• Cecilia I. Attorresi,
• Javier A. Ramírez and
• Daniel G. Rivera

Beilstein J. Org. Chem. 2019, 15, 1236–1256, doi:10.3762/bjoc.15.121

• hormonal ones. All steroids are based on a common skeleton containing three fused six-membered rings and one five membered ring. This fused-ring system provides a readily available source of rigidity and chirality, whose substituents can be oriented either towards the α- or the β-face. Steroids feature a