CF₃-substituted carbocations: underexploited intermediates with great potential in modern synthetic chemistry

• Anthony J. Fernandes,
• Armen Panossian,
• Bastien Michelet,
• Agnès Martin-Mingot,
• Frédéric R. Leroux and
• Sébastien Thibaudeau

Beilstein J. Org. Chem. 2021, 17, 343–378, doi:10.3762/bjoc.17.32

• amount of the moderately acidic (S)-TRIP (pKa = 3–4 in DMSO [113][114]) in dichloromethane afforded the chiral α-(trifluoromethyl)aminoaryl derivatives 177 in an excellent yield and enantiomeric excess (Scheme 42). The authors proposed that hemiacetal 175 and amine 176 react under the reaction conditions

The preparation and properties of 1,1-difluorocyclopropane derivatives

• Kymbat S. Adekenova,
• Peter B. Wyatt and
• Sergazy M. Adekenov

Beilstein J. Org. Chem. 2021, 17, 245–272, doi:10.3762/bjoc.17.25

• corresponding monoacetate through Alcaligenes sp. lipase-catalyzed hydrolysis with >99% enantiomeric excess. Kirihara et al. have reported the synthesis of the separate enantiomers of 2,2-difluoro-1-aminocyclopropanecarboxylic acid, which are analogs of the naturally occurring 1-aminocyclopropanecarboxylic acid

Insight into functionalized-macrocycles-guided supramolecular photocatalysis

• Minzan Zuo,
• Krishnasamy Velmurugan,
• Kaiya Wang,
• Xueqi Tian and
• Xiao-Yu Hu

Beilstein J. Org. Chem. 2021, 17, 139–155, doi:10.3762/bjoc.17.15

• the modified CDs 7a–9a as sensitizing hosts and (Z)-6 as the guest (Figure 5 and Figure 6) [24]. The compounds 8a, 8b, and 8e could yield a higher enantiomeric excess (10.7% ee in 2 min at 25 °C, host occupancy 91%, 23.9% ee in 25 min at 40 °C, host occupancy 98%, and 8.1% ee in 30 min at 25 °C, host

Recent progress in the synthesis of homotropane alkaloids adaline, euphococcinine and N-methyleuphococcinine

• Dimas J. P. Lima,
• Antonio E. G. Santana,
• Michael A. Birkett and
• Ricardo S. Porto

Beilstein J. Org. Chem. 2021, 17, 28–41, doi:10.3762/bjoc.17.4

• tetroxide and potassium periodate, to provide (−)-adaline (1) and (−)-euphococcinine (2). Originally, Yu et al. synthesized (−)-adaline (1) with good yields and high enantiomeric excess using catalytic asymmetric allylation from commercially available 58. Additionally, intramolecular allylic transfer led to

• subjected to simultaneous catalytic hydrogenation and hydrogenolysis of the protecting group Cbz to give (−)-adaline (1) in 90% yield. The asymmetric synthesis achieved by Liebeskind et al. presented a high enantiomeric excess and good yields. Also, the proposed route differed from the previously mentioned

• in terms of common intermediaries. Therefore, it’s a new synthesis of (−)-adaline (1) and might eventually be applied to related homotropanes. In conclusion, (−)-adaline (1) was obtained in 14 steps from 66 using a new scaffold-based semipinacol/1,5-Michael-like strategy. The enantiomeric excess for

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

• on subsequent Tamao–Fleming oxidation provided the exo-diol 18 in an overall good yield with 99% enantiomeric excess (Scheme 3). Furthermore, the diol 18 was converted into the corresponding diketone 19 using pyridinium chlorochromate (PCC) as an oxidizing agent. Interestingly, they have also

Controlling the stereochemistry in 2-oxo-aldehyde-derived Ugi adducts through the cinchona alkaloid-promoted electrophilic fluorination

• Yuqing Wang,
• Gaigai Wang,
• Anatoly A. Peshkov,
• Ruwei Yao,
• Muhammad Hasan,
• Manzoor Zaman,
• Chao Liu,
• Stepan Kashtanov,
• Olga P. Pereshivko and
• Vsevolod A. Peshkov

Beilstein J. Org. Chem. 2020, 16, 1963–1973, doi:10.3762/bjoc.16.163

• asymmetric electrophilic fluorination for derivatizing the 2-oxo-aldehyde-derived Ugi adducts. This allowed us to obtain the post-Ugi products fluorinated at the peptidyl position with the enantiomeric excess values in several instances reaching more than 70%. Molecular representation of the X-ray crystal

Stereoselective Biginelli-like reaction catalyzed by a chiral phosphoric acid bearing two hydroxy groups

• Xiaoyun Hu,
• Jianxin Guo,
• Cui Wang,
• Rui Zhang and
• Victor Borovkov

Beilstein J. Org. Chem. 2020, 16, 1875–1880, doi:10.3762/bjoc.16.155

• ago [10], little attention was given to asymmetric pathways. Only in 2003, Juaristi and Muñoz-Muñiz have reported the reaction of benzaldehyde, urea, and methyl acetoacetate using a chiral amide with CeCl3 for the first time. However, only 40% enantiomeric excess (ee) was obtained [11]. Then, Zhu

• -341 Mc polarimeter. Melting points were determined on a VEB Wägetechnik Rapio PHMK05 instrument, and are uncorrected. Enantiomeric excess (ee) values were analyzed by a Thermo UltiMate 3000 HPLC and SHIMADZU LC-20 AR at room temperature with n-hexane/isopropanol as eluent. Diethyl ʟ-tartrate was

Pd-catalyzed asymmetric Suzuki–Miyaura coupling reactions for the synthesis of chiral biaryl compounds with a large steric substituent at the 2-position

• Yongsu Li,
• Bendu Pan,
• Xuefeng He,
• Wang Xia,
• Yaqi Zhang,
• Hao Liang,
• Chitreddy V. Subba Reddy,
• Rihui Cao and
• Liqin Qiu

Beilstein J. Org. Chem. 2020, 16, 966–973, doi:10.3762/bjoc.16.85

• silica gel. The enantiomeric excess value of the product was determined by HPLC by using an AD-H, OD-H or IA-3 column. (R)-MeO-MOP and our ligands. Asymmetric Suzuki–Miyaura coupling. Reaction conditions: 1 equiv N-aryl-bromoaryl compounds, 2 equiv arylboronic acids, 5 mol % Pd, 6 mol % ligand, 3 equiv

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

• dichloromethane/petroleum ether) to give CF2-substituted aziridine 4. The enantiomeric excess was determined by chiral HPLC analysis. See Supporting Information File 1 for the dissolution–filtration procedure for each compound. Preparation of chiral aziridines from fluorinated diazo reagents. Substrate scope of

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

• catalyst worked well for various (Z)-isomer substrates. Opposite enantiomers were obtained from (Z)- and (E)-isomers, with a higher enantiomeric excess from the (Z)-isomer. Keywords: catalyst; chiral NHC; conjugate reduction; copper catalysis; enantioselective reaction; Introduction Since the leading

• ligand on the copper-catalyzed enantioselective conjugate reduction of α,β-unsaturated esters with hydrosilanes, placing a focus on (Z)-isomer substrates, which generally gave slightly lower enantiomeric excess with the chiral bisphosphines compared to the (E)-isomer substrates. Results and Discussion

[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

• appeared to be quite low due to the significant racemization of the phosphorus center under the applied conditions. On the other hand, the treatment of (SP)-60 with Lewis acid led to the formation of chiral γ-mercaptoalkylphosphine oxide 46 in good yield and with only slight decrease in enantiomeric excess

• pseudorotation. This, in turn, should have led to a remarkable deterioration of the enantiomeric excess of the product. The same might be postulated for the rearrangement of alkenylphosphine sulfide 65, which should form a pentavalent intermediate equally well. In the next step, the enantiomerically enriched β

• 67, and S-acylated γ-mercaptoalkylphosphine oxide 68. Compound 66 was obtained with complete stereoselectivity, whereas the enantiomeric excess of both 67 and 68 was higher, 78% ee and 76% ee, respectively. The phosphine sulfides (SP)-19 and (SP)-20 underwent rearrangement to the corresponding chiral

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

• cathode in an undivided cell in the presence of cinchonidine alkaloid as the source of chirality [30]. They modified the electrolysis conditions using a mixture of CH3CN/H2O and tetraethylammonium iodide as the supporting electrolyte and achieved a slight improvement in the enantiomeric excess (Scheme 7

• of 38 to the corresponding sulfoxide 39 with excellent chemical yield although the value of enantiomeric excess was considerably low (Scheme 16) [46]. A few years later, Komori and Nonaka, in two consecutive reports, established a modified method for the asymmetric electrochemical oxidation of alkyl

• aryl sulfides 40 to their corresponding sulfoxides 41 using poly(amino acid)-coated platinum electrodes with moderate yield and good to excellent enantiomeric excess (Scheme 17) [47][48]. Osa and co-workers, in 1994, made an important contribution in the area by developing an enantioselective method

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

• a palladium catalyst (Scheme 9). Under these conditions, the fluorination of ethyl 2-cyano-2-phenylacetate afforded the product with highest enantiomeric excess (93%). In 2013, Kim’s group [46] described an enantioselective electrophilic fluorination of α-chloro-β-keto phosphonates with up to 95% ee

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

• degassed by the freeze-pump-thaw method, the catalysis was performed under inert gas conditions (Argon), and the chemical conversions and yields were determined by 1H NMR spectroscopy (see Supporting Information File 1). The enantiomeric excess of the product 14 was determined after conversion with (2S,4S

• )-(+)-pentanediol into diastereomers and by integration of the corresponding signals in the 1H NMR spectrum. In all experiments with NDI 1 the enantiomeric excess exceeded a value of 78%; in all experiments with cNDI 6 the enantiomeric excess was higher than 81%. This parameter is omitted for clarity in the

Fluorine-containing substituents: metabolism of the α,α-difluoroethyl thioether motif

• Andrea Rodil,
• Alexandra M. Z. Slawin,
• Nawaf Al-Maharik,
• Ren Tomita and
• David O’Hagan

Beilstein J. Org. Chem. 2019, 15, 1441–1447, doi:10.3762/bjoc.15.144

• significantly more slowly to the sulfone. When the substrate was (p-OMe)PhSCF2CH3, then the resultant (demethylated) phenol sulfoxide had an enantiomeric excess of 60%, and when the substrate was the β-substituted-SCF2CH3 naphthalene, then the enantiomeric excess of the resultant sulfoxide was 54%. There was no

• we could not determine the absolute stereochemistry of the predominant enantiomer, it was clear from the assay that there was a significant enantiomeric ratio (4:1) of 6 which translates to a 60% enantiomeric excess (ee, see Supporting Information File 1). We note that there have been chemical

Efficient resolution of racemic crown-shaped cyclotriveratrylene derivatives and isolation and characterization of the intermediate saddle isomer

• Sven Götz,
• Andreas Schneider and
• Arne Lützen

Beilstein J. Org. Chem. 2019, 15, 1339–1346, doi:10.3762/bjoc.15.133

• phase (Figure 1). This simple procedure was successfully used for the semi-preparative separation of 156 mg of (rac)-1. It was possible to separate more than 25 mg substance per injection giving both enantiomers of 1 in an enantiomeric excess of >99%. Electronic circular dichroism spectra (ECD) were

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

• chromatography on silica gel using n-hexane/EtOAc as eluent. Enantiomeric excess (ee) was determined by chiral HPLC analysis through comparison with the authentic racemic material. Assignment of the stereoisomers was performed by comparison with literature data. Synthesis and characterization Prolyl pseudo

• flash column chromatography (EtOAc/hexane 1:9, v/v). The spectroscopic data are in agreement with the published data [15]. The enantiomeric excess was determined by chiral-stationary phase HPLC (Chiralpak OD-H, hexane/iPrOH 99:1, v/v, 25 °C) at 1.00 mL/min, UV detection at 210 nm: tR: (syn, major

Mechanistic investigations on multiproduct β-himachalene synthase from Cryptosporangium arvum

• Jan Rinkel and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2019, 15, 1008–1019, doi:10.3762/bjoc.15.99

• of GPP and GGPP, respectively. Compounds known to also originate from non-enzymatic hydrolysis are labelled with an asterisk. The enantiomeric excess values were determined based on GC analysis on a chiral phase. EI mass spectrum of 1 arising from an incubation of (2-2H)GPP and IPP with FPPS and HcS

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

• evaluated in several enantioselective reactions, specifically in the asymmetric allylic amination (AAA), which showed a promising enantiomeric excess of up to 75% ee. Furthermore, a new disubstituted α-CD catalyst was prepared as a pure AD regioisomer and also tested in the AAA. Our results indicate that (i

• 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

• alkaloids have never been prepared and tested in asymmetric organocatalysis. Thus, in this study, we investigated methods for attaching cinchona alkaloids to CD skeletons, and we assessed the enantiomeric excess of the resulting CD derivatives as organocatalysts in asymmetric reactions, specifically in the

Synthesis of acylglycerol derivatives by mechanochemistry

• Karen J. Ardila-Fierro,
• Andrij Pich,
• Marc Spehr,
• José G. Hernández and
• Carsten Bolm

Beilstein J. Org. Chem. 2019, 15, 811–817, doi:10.3762/bjoc.15.78

• epoxides, for which the maximum theoretical yield of the reaction is 50%. Here, however, the yield of the sn-1,3-protected monoacylglycerol was high, and consequently we expected the enantiomeric excess of the product to be low. This, assumption was confirmed by analysis of the sample by high-performance

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

• bearing two adjacent quaternary stereogenic centers in a single pot operation. The simple preparation of enantiomerically enriched cyclopropene afforded the corresponding cyclopropanols in high enantiomeric excess. This transformation was then applied to unfunctionalized diversely substituted

A chemoenzymatic synthesis of ceramide trafficking inhibitor HPA-12

• Seema V. Kanojia,
• Sucheta Chatterjee,
• Subrata Chattopadhyay and
• Dibakar Goswami

Beilstein J. Org. Chem. 2019, 15, 490–496, doi:10.3762/bjoc.15.42

• chicken liver esterase proceeded with modest enantioselectivity [41][42]. Rhizopus arrhizus-mediated hydrolysis of the acetate furnished the enantiomerically pure alcohol (99% ee), however, the enantiomeric excess (ee) of the antipode acetate was very poor (5–9%) [43]. On the other hand, the Amano PS

• absolute configurations of (R)-5 and (S)-4 were assigned by comparison of the chiroptical data with those reported [45]. The stereochemical outcome of the reaction is consistent with Kazlauskas’ empirical rule [51]. The conversion (% c) and the enantiomeric excess (E) values were calculated according to

Silanediol versus chlorosilanol: hydrolyses and hydrogen-bonding catalyses with fenchole-based silanes

• Falco Fox,
• Jörg M. Neudörfl and
• Bernd Goldfuss

Beilstein J. Org. Chem. 2019, 15, 167–186, doi:10.3762/bjoc.15.17

• dichloromethane (DCM) and 1,2-dichloroethane (1,2-DCE) the reaction takes place but without any enantiomeric excess (ee) (Table 7, entries 2 and 3). In DCM the highest yield is isolated, but that is due to a fast background reaction [45]. With toluene as solvent, no background reaction is observed (Table 9, entry

• 9). To stabilize and improve the ion pair, polar solvents are tested as diethyl ether and dimethylformamide gave no conversion and starting material is obtained (Table 7, entries 4 and 5), acetonitrile and acetone increase the yield (Table 7, entries 6 and 7), but without any enantiomeric excess. In

• the yields and the enantiomeric excess. In a third reaction, the 1,4 addition of silyl keten acetals 11 to chromone 20 is investigated (Table 11, Scheme 8). Chromone 20 is first transformed to the oxonium ion pair 21. Catalyst BIFOXSi(OH)2 (9) binds the triflate anion via hydrogen bonding and leaves

Asymmetric synthesis of a high added value chiral amine using immobilized ω-transaminases

• Antonella Petri,
• Valeria Colonna and
• Oreste Piccolo

Beilstein J. Org. Chem. 2019, 15, 60–66, doi:10.3762/bjoc.15.6

• and in a semi-continuous system. The selected biocatalyst showed good stability under the reaction conditions providing consistent results in terms of conversion and enantiomeric excess after several cycles. The reported results may be of practical interest in view of the development of this

• enantioselectivity (>99%) but longer reaction times were required to achieve high yields of up to 94% (Table 1, entries 6, 7, and 8). It should be noted that the TAs-IMB enzymes showed excellent enantioselectivities as demonstrated by the enantiomeric excess values which were all above 98%. Therefore, these results

• represent an improvement in the preparation of enantiomerically pure 2 compared with literature data [23]. Höhne et al. obtained only the (R)-enantiomer in 42% yield and 97% ee as a result of kinetic resolution of 1 using ω-transaminase and pyruvate as an amine acceptor. The enantiomeric excess in entries 9

Ruthenium-based olefin metathesis catalysts with monodentate unsymmetrical NHC ligands

• Veronica Paradiso,
• Chiara Costabile and
• Fabia Grisi

Beilstein J. Org. Chem. 2018, 14, 3122–3149, doi:10.3762/bjoc.14.292

• use of any halide additive. The unsymmetrical NHC catalysts 164, 173 and 174 were also examined in the asymmetric synthesis of [7]helicene (180). Among them, complex 174 exhibited the highest degree of selectivity, leading to the desired product with an enantiomeric excess of 80% [56]. An extension of