Evaluation of the enantioselectivity of new chiral ligands based on imidazolidin-4-one derivatives

• Jan Bartáček,
• Karel Chlumský,
• Jan Mrkvička,
• Lucie Paloušová,
• Miloš Sedlák and
• Pavel Drabina

Beilstein J. Org. Chem. 2024, 20, 684–691, doi:10.3762/bjoc.20.62

• , the other afforded the nitroaldols with ee values of 60–90%. Finally, the complexes of ligands with cis-cis configuration (Ic and IIc) were evaluated. These catalyst are the most efficient catalysts, producing nitroaldols with very high enantiomeric purity (approx. 90–95% ee). This finding contrasts

• pyridine to imidazole lowered the reaction rate but did not alter the critical role of configuration at position 2 in determining the enantiomeric purity of the final product. Furthermore, the study of “proline-type” derivative IV underscored the importance of position 2 in chirality transfer, although

Application of N-heterocyclic carbene–Cu(I) complexes as catalysts in organic synthesis: a review

• Nosheen Beig,
• Varsha Goyal and
• Raj K. Bansal

Beilstein J. Org. Chem. 2023, 19, 1408–1442, doi:10.3762/bjoc.19.102

• improvement in the enantiomeric purity of the product (>98% conv., 85.5:14.5 er) was achieved while using the naphthyl-substituted salt 163 (Scheme 64). Besides, a highly enantioselective catalytic hydroboration could be achieved from several exocyclic 1,1-disubstituted alkenes 164; in this transformation

Enolates ambushed – asymmetric tandem conjugate addition and subsequent enolate trapping with conventional and less traditional electrophiles

• Péter Kisszékelyi and
• Radovan Šebesta

Beilstein J. Org. Chem. 2023, 19, 593–634, doi:10.3762/bjoc.19.44

• enantiomeric purity. Further transformations of the products were demonstrated in several examples, including reduction, acidic deprotection and subsequent base-mediated cyclization, or Baeyer–Villiger oxidation. At about the same time, Huang and co-workers have developed similar asymmetric tandem sequences

Combretastatins D series and analogues: from isolation, synthetic challenges and biological activities

• Jorge de Lima Neto and
• Paulo Henrique Menezes

Beilstein J. Org. Chem. 2023, 19, 399–427, doi:10.3762/bjoc.19.31

• , overall yield of 29% from 52) (Scheme 15). Using this strategy, combretastatin D-1 (1) was obtained in an enantiomeric purity of 96%, making it possible to establish the absolute configuration of the epoxide. Further, X-ray crystallographic analysis corroborated with the results obtained by Rychnovsky and

The stereochemical course of 2-methylisoborneol biosynthesis

• Binbin Gu,
• Anwei Hou and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2022, 18, 818–824, doi:10.3762/bjoc.18.82

• stereoisomers (5:2) that were separated by column chromatography (Scheme 2). Reduction of (E)-3 with DIBAl-H gave 2-methylgeraniol (4) that was converted under Sharpless conditions [36] into the epoxides (2R,3R)-5a using ᴅ-(−)-diisopropyl tartrate (DIPT) and (2S,3S)-5b with ʟ-(−)-DIPT. The enantiomeric purity

• %) (structures are shown in Figure 2). Reproducibility of these results was demonstrated in triplicates. While these data showed that enantiomerically enriched (R)-2-Me-LPP is more efficiently converted into 1 than the enriched S enantiomer, the enantiomeric purity of the substrates was not sufficiently high to

• with calf intestinal phosphatase (CIP). The thus obtained compounds 6a and 6b were analyzed by gas chromatography on a chiral stationary phase, revealing that the materials were unchanged and still of very high enantiomeric purity (>99% ee, Figure S5 in Supporting Information File 1). Conversion of

The asymmetric Henry reaction as synthetic tool for the preparation of the drugs linezolid and rivaroxaban

• Martin Vrbický,
• Karel Macek,
• Jaroslav Pochobradský,
• Jan Svoboda,
• Miloš Sedlák and
• Pavel Drabina

Beilstein J. Org. Chem. 2022, 18, 438–445, doi:10.3762/bjoc.18.46

• -2-one antibiotics only the S-enantiomers are able to block bacterial ribosomes, which leads to the prevention of translation processes in bacteria [9][10]. With regards to these facts, a high enantiomeric purity is one of the fundamental requirements in the production of such pharmaceutical

• 15 and 19 was also performed with the aim to increase the enantiomeric purity of the corresponding nitroaldol products 21–26. The structural modification consisted in the introduction of different alkyl moieties to the carbamate functional group of the aldehyde intermediates 15–20. As bulky and/or

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

• reaction with an electron-donating p-MeO-substituted benzylidene oxindole was very sluggish and did not reach full conversion (Scheme 2, 3m). The product 3m was obtained with only 36% yield and with undetermined enantiomeric purity, since the peaks were not separable in various HPLC methods. Similarly, the

Regioselective synthesis of methyl 5-(N-Boc-cycloaminyl)-1,2-oxazole-4-carboxylates as new amino acid-like building blocks

• Jolita Bruzgulienė,
• Greta Račkauskienė,
• Aurimas Bieliauskas,
• Vaida Milišiūnaitė,
• Miglė Dagilienė,
• Gita Matulevičiūtė,
• Vytas Martynaitis,
• Sonata Krikštolaitytė,
• Frank A. Sløk and
• Algirdas Šačkus

Beilstein J. Org. Chem. 2022, 18, 102–109, doi:10.3762/bjoc.18.11

• hydroxylamine hydrochloride in methanol (Scheme 1). Synthesized compounds 4b–g exhibited optical activity, and the corresponding (R)- or (S)-enantiomers rotated the plane of plane-polarized light in opposite directions. The enantiomeric purity of chiral compounds 4b–g was assessed via chiral HPLC analysis of

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

• ratio of 86:14 and high enantiomeric purity of 95:5 er for the major diastereomer (Table 1, entry 1). Using chloroform/isopropyl alcohol 9:1 as the solvent mixture afforded after 120 hours, aldehyde 10a in 45% yield with 83:17 dr and 97:3 er (Table 1, entry 2). The Michael addition in methanol catalyzed

• by only 3 mol % (S,R)-C1 after 72 hours provided only 18% yield, but with high enantiomeric purity (99:1, Table 1, entry 5). The reaction without a base did not provide the desired product 10a (Table 1, entry 6). Moreover, a reaction performed with other acidic additives (phenylboronic acid, p

• -toluenesulfonic acid) provided after 72 hours only 18% and 23% yield of the product with compromised diastereomeric and enantiomeric purity (Table 1, entries 3 and 4). When, we applied 3 mol % of catalyst (S,R)-C1 during 48 hours, we obtained 73% yield with diastereomeric purity 83:17 and high enantiomeric purity

Enantioselective PCCP Brønsted acid-catalyzed aminalization of aldehydes

• Martin Kamlar,
• Robert Reiberger,
• Martin Nigríni,
• Ivana Císařová and
• Jan Veselý

Beilstein J. Org. Chem. 2021, 17, 2433–2440, doi:10.3762/bjoc.17.160

• the enantioselectivity of the aminalization reaction. While most solvents tested showed to be effective at room temperature, the enantiomeric purity of the corresponding aminal 3a was low in all cases (Table 1, entries 1–5). On the other hand, the yield of 3a was satisfactory in all reactions. In

• optimal for the enantiocontrol of the model reaction, affording the product 3a in 90% yield with an enantiomeric purity of 66% ee (Table 1, entry 7). Additionally, the effect of molecular sieves on the course of the reaction was investigated and the obtained results demonstrated that molecular sieves

• dramatically improved the enantioselectivity (Table 1, entries 9–11). In particular, when the aminalization reaction between 1a and 2a was carried out in the presence of 5 Å molecular sieves, the corresponding product 3a was delivered in high yield (96%) and with enantiomeric purity 80% ee (Table 1, entry 11

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

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

• amide, confirming to be a sample with a high level of enantiomeric purity. As in Murahashi’s synthesis, Meyers also utilized a chiral auxiliary for asymmetric induction. Nonetheless, this method differed from Murahashi's by presenting a diastereoselective intramolecular Mannich cyclization to form the

Synthesis of monophosphorylated lipid A precursors using 2-naphthylmethyl ether as a protecting group

• Jundi Xue,
• Ziyi Han,
• Gen Li,
• Khalisha A. Emmanuel,
• Cynthia L. McManus,
• Qiang Sui,
• Dongmian Ge,
• Qi Gao and
• Li Cai

Beilstein J. Org. Chem. 2020, 16, 1955–1962, doi:10.3762/bjoc.16.162

• )-3-hydroxytetradecanoate (5) in 98% yield. The same hydrogenation reaction was carried out using the (S)-Ru(OAc)2(BINAP) catalyst. Then both the R and S products were compared using chiral HPLC to confirm the absolute configuration and enantiomeric purity (Figure S1, Supporting Information File 1

Fluorinated phenylalanines: synthesis and pharmaceutical applications

• Laila F. Awad and
• Mohammed Salah Ayoup

Beilstein J. Org. Chem. 2020, 16, 1022–1050, doi:10.3762/bjoc.16.91

• product 2-[18F]FPhe 46 in 43% yield, whereas under microwave irradiation a 34% yield was obtained. Under the optimized conditions, the enantiomeric purity was reported to be ≥94% ee [46] (Scheme 10). 1.3. Photooxidative cyanation of fluorinated benzylamine A convenient, protecting group-free, and

Copper-catalysed alkylation of heterocyclic acceptors with organometallic reagents

• Yafei Guo and
• Syuzanna R. Harutyunyan

Beilstein J. Org. Chem. 2020, 16, 1006–1021, doi:10.3762/bjoc.16.90

• the synthesis of the corresponding products with good yield and enantiomeric purity (up to 83% yield and 97% ee). Furthermore, a large variety of vinylalanes was investigated, and the product 2l was further derivatised into a chiral bicyclic structure (5, Scheme 2A). In addition, simple vinyl

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

• et. al. [82]. The starting dienynes were obtained in a high enantiomeric purity starting form 2,6-dimethyl-1,4-benzoquinone and isoprene via an asymmetric Diels–Alder reaction. The domino metathesis reactions induced by the Grubbs second-generation catalyst proceeded in good yield (92%) thereby

Synthesis of disparlure and monachalure enantiomers from 2,3-butanediacetals

• Adam Drop,
• Hubert Wojtasek and
• Bożena Frąckowiak-Wojtasek

Beilstein J. Org. Chem. 2020, 16, 616–620, doi:10.3762/bjoc.16.57

• ), (−)-monachalure (4, (7S,8R)-cis-7,8-epoxyoctadecane) and their olefinic precursors in addition to (+)-disparlure (1) [11][12]. For the gypsy moth a high enantiomeric purity of (+)-disparlure (>98% ee) is required to evoke the male’s sexual response and even a small percentage of (−)-disparlure abolishes the

• also been described [29]. However, many of these methods have some drawbacks – the most important one being the insufficient enantiomeric purity for biological and commercial applications [29]. (+)-Disparlure used in most commercial lures is prepared by the Sharpless epoxidation reaction, which gives

• disparlure and monachalure with high enantiomeric purity. It can also be adapted for preparation of other chiral cis-epoxides. 2,3-Butanediacetals obtained from tartaric acid dimethyl diester contain protected hydroxy groups and two functional groups suitable for the attachment of various substituents. trans

Synthesis and circularly polarized luminescence properties of BINOL-derived bisbenzofuro[2,3-b:3’,2’-e]pyridines (BBZFPys)

• Ryo Takishima,
• Yuji Nishii,
• Tomoaki Hinoue,
• Yoshitane Imai and
• Masahiro Miura

Beilstein J. Org. Chem. 2020, 16, 325–336, doi:10.3762/bjoc.16.32

• ), 7.94 (d, J = 8.9 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ 31.25, 34.61, 110.62, 117.54, 123.49, 124.01, 126.36, 129.35, 131.34, 131.42, 146.69, 152.29; HRMS–APCI (m/z): [M + H]+ calcd for C28H31O2, 399.2330; found, 399.2319. The enantiomeric purity was confirmed by HPLC analysis: CHIRAL ART Amylose-SA

• ), 19F NMR (376 MHz, CDCl3) δ 69.06; HRMS–APCI (m/z): [M + H]+ calcd for C38H35F2N2O2, 589.2644; found, 589.2661. The enantiomeric purity was confirmed by HPLC analysis: CHIRAL ART Cellulose-SB column, n-hexane/chloroform 95:5, 1.0 mL/min, 40 °C; (S)-2: tR = 9.86 min, (R)-2: tR = 21.29 min, UV detection

• , 121.55, 122.67, 123.15, 124.27, 125.03, 126.13, 129.10, 129.30, 130.90, 132.04, 141.35, 147.49, 149.54, 154.00, 161.86, 162.48; HRMS–APCI (m/z): [M + H]+ calcd for C50H45N2O4, 737.3367; found, 737.3374. The enantiomeric purity was confirmed by HPLC analysis: CHIRAL ART Amylose-SA column, n-hexane

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

• electrohydrogenation of 12b that resulted in improved yield and enantiomeric purity as compared to previously reported methods (Scheme 11). In another report the same reaction was discovered to be catalyzed by applying copper nanoparticle (CuNP) as a cathode for elelctrohydrogenation of 12 [39]. The asymmetry was

Chiral terpene auxiliaries V: Synthesis of new chiral γ-hydroxyphosphine oxides derived from α-pinene

• Anna Kmieciak and
• Marek P. Krzemiński

Beilstein J. Org. Chem. 2019, 15, 2493–2499, doi:10.3762/bjoc.15.242

• % yield) allowed to upgrade the enantiomeric purity of dIpc2BH [25]. Oxidation of the resulting dialkylborane with hydrogen peroxide provided enantiomerically pure (−)-isopinocampheol (7) in 78% yield. The Brown–Garg protocol [26] was employed to oxidize 7 with an aqueous solution of sodium dichromate and

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

• P-2000 polarimeter. The enantiomeric purity of diols was determined by chiral-phase HPLC analysis on Daicel Chiralpak ID (250 mm × 4.6 mm inside diameter) using a hexane/iPrOH mixture as a mobile phase. Thin-layer chromatography (TLC) was performed using Merck Silica Gel GF254, 0.20 mm thickness

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

• for structural enlargement and at least one stereogenic center which is usually transferred into the final product. To assure the highest possible enantiomeric purity chirons are obtained in most instances from natural products like carbohydrates, amino acids, hydroxy acids or terpenes. 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

• and 10.0 min, respectively, demonstrating that P5A-DPA was the racemic mixture of Rp and Sp configuration. The two fractions were collected separately and re-injected into the chiral column to confirm the enantiomeric purity and to check if racemization of the enantiomers takes place in solution at

Synthesis of nonracemic hydroxyglutamic acids

• Dorota G. Piotrowska,
• Iwona E. Głowacka,
• Andrzej E. Wróblewski and
• Liwia Lubowiecka

Beilstein J. Org. Chem. 2019, 15, 236–255, doi:10.3762/bjoc.15.22

• was much lower (2.6:1 and 1:1, respectively). Acid hydrolysis of 64 gave (4S)-4-hydroxy-L-glutamic acid [(2S,4S)-3] as the hydrochloride, however, its enantiomeric purity was not checked. In connection with the total synthesis of thiopeptide antibiotic nosiheptide an orthogonally protected (4S)-4

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

• available (+)-fenchone has 98% enantiomeric purity, BIFOXSi(OH)2 can be further purified. rac-BIFOXSi(OH)2 crystallizes as a dimer from toluene (Figure 14). BIFOXSi(OH)2 (9) crystallizes as a tetramer from n-hexane (Figure 15), where six OH groups build a network of hydrogen bonds. Thus the polar core is