Synthesis of depressin, cryptomeridiol and 4-epi-cryptomeridiol enabled by a terpenoid chiral pool-producing platform

• Yao Kong,
• Tao Wang,
• Chen Wang,
• Pengcheng Zhang,
• Yuanning Liu,
• Kaibiao Wang,
• Fen Liu,
• Hongli Jia and
• Zhengren Xu

Beilstein J. Org. Chem. 2026, 22, 683–690, doi:10.3762/bjoc.22.53

• conditions, affording 9-hydroxy-13-ketocasbene (10, 21%) and 5-hydroxy-13-ketocasbene (11, 20%), respectively, as single diastereomers. Although the orientation of the newly introduced hydroxy group could not be assigned solely based on NMR analysis, the 5-hydroxy group of 11 will be transformed into a

• ). Supporting Information Supporting Information File 5: Materials, synthetic methods and copies of NMR spectra for all compounds. Supporting Information File 6: X-ray crystal structure of 16. Funding We are grateful to the National Natural Science Foundation of China (No. 82574274) for the financial support.

Harnessing light energy with molecules

• Grace G. D. Han,
• Mogens Brøndsted Nielsen and
• Hermann A. Wegner

Beilstein J. Org. Chem. 2026, 22, 680–682, doi:10.3762/bjoc.22.52

• -workers [4], the π-system of monoaryl-substituted NBDs was synthetically extended by acetylenic bridges. In addition, Hebborn, Ihmels, and co-workers [5] show that 19F NMR spectroscopy enables unambiguous identification of mono- and bisQC intermediates in the sequential photoreactions of a fluorinated

• trisNBD-benzene, overcoming the signal overlap that limits conventional 1H NMR analysis. Further, the consequences on the absorption properties, photoisomerization, and QC lifetime were studied. In another article by Krappmann and Hirsch [6], the implications of replacing the methylene bridge of the NBD

Photoorganocatalytic trifluoromethylation of (het)arenes in green conditions

• Egor N. Boronin,
• Svetlana E. Kaurkina,
• Milena M. Svetlakova,
• Anton S. Bolshakov,
• Maxim V. Arsenyev,
• Vasilii F. Otvagin,
• Alexey Yu. Fedorov,
• Timothy Noël and
• Alexander V. Nyuchev

Beilstein J. Org. Chem. 2026, 22, 662–671, doi:10.3762/bjoc.22.50

• analyzed by q19F NMR spectroscopy. Only trace amounts of the trifluoromethylated product were detected, whereas the TEMPO adducts of the trifluoromethyl and trifluoroacetyl radicals were observed in 16% and 22% yield, respectively (Scheme 3). Stern–Volmer studies of the quenching of the photocatalyst

• Information Supporting Information File 2: Experimental part, copies of NMR spectra and computational data. Acknowledgements We thank Dr. Y.B. Malysheva for registration of NMR spectra and S.A. Churkin for technical support. Funding The research was carried out in Laboratory “Chemistry of natural products

Hydrogen production from formic acid catalyzed by NHC–Cu complexes

• Orlando Santoro and
• Catherine S. J. Cazin

Beilstein J. Org. Chem. 2026, 22, 620–627, doi:10.3762/bjoc.22.48

• (Scheme 1). To support these working hypotheses, the reaction of 1 equiv [Cu(OH)(IPr)] with 2 equiv of formic acid in a sealed tube was followed by 1H NMR spectroscopy in deuterated toluene (C7D8). After 16 h at 110 °C, the formation of 1b was observed while no excess of formic acid was detected

• . Interestingly, by adding to the reaction mixture a further equivalent of FA, evolution of gas was observed and H2 was detected by NMR spectroscopy (see Supporting Information File 1, Figure S1). This highlighted the formation in situ of the Cu–H species by decarboxylation of 1b. To quantify the amount of gas

• Information File 16: Detailed description of the procedure for the gas evolution experiments, NMR spectra of isotopic labeling experiments. Acknowledgements The authors gratefully acknowledge Sasol Technology (UK) Ltd. for GC analyses. Funding The authors gratefully acknowledge the UGent BOF, the Royal

Towards the targeted protein degradation of CK2: design and synthesis of CAM4066-based PROTACs

• Sophie Day-Riley,
• Sona Krajcovicova,
• Aryaman Raj Sokhal,
• Jan L. Venne,
• Paul Brear,
• Marko Hyvönen,
• Benjamin C. Whitehurst,
• Jason S. Carroll and
• David R. Spring

Beilstein J. Org. Chem. 2026, 22, 611–619, doi:10.3762/bjoc.22.47

• = dimethylformamide; HATU = O-(7-azabenzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate; THPTA = tris(3-hydroxypropyltriazolylmethyl)amine; TFA = trifluoroacetic acid; VHL = von Hippel–Lindau. Supporting Information Supporting Information File 14: Experimental part and copies of NMR spectra

• . Acknowledgements The authors are grateful to Kristina Kostadinova and Dr Marc de la Roche for the help with the Western Blot analysis, to Dr Eleanor Atkinson and Dr Jessica Iegre for their prior work on CK2 inhibitors, and to Dr Michal Malon for his help with several NMR assignments. We are grateful for the

Regioselective approach to 5-arylsulfonylisoxazoles and their antimicrobial activity

• Artem S. Sazonov,
• Dmitry A. Vasilenko,
• Denis V. Porfiriev,
• Yuri K. Grishin,
• Rimma A. Gazzaeva,
• Alisa P. Chernyshova,
• Maxim A. Kryakvin,
• Anna A. Baranova,
• Vera A. Alferova and
• Elena B. Averina

Beilstein J. Org. Chem. 2026, 22, 592–602, doi:10.3762/bjoc.22.45

• using 1H NMR (Figure S1 in Supporting Information File 1). The results revealed that the oxidation of isoxazole 2a to sulfoxide 4a proceeds quickly, and complete conversion of isoxazole 2a is achieved within 5 min. In contrast, the subsequent reaction of 4a to 3a proceeds is much slower, and only after

• 4 hours does the C(4)–H signal of compound 4a at δ 7.05 ppm in the 1H NMR spectra finally disappear. With optimized conditions in hand, we turned our attention to examine the substrate scope. As shown in Scheme 3, isoxazole derivatives bearing different electron-withdrawing groups in position 3 such

• conditions. MIC (μg/mL) against bacterial and fungal lines. Supporting Information Supporting Information File 8: General synthetic and biological procedures, characterization data and copies of 1H, 13C{1H}, 19F, 31P, 1H-13C HSQC, 1H-13C HMBC NMR spectra, HRMS spectra and the results of the elemental

Continuous-flow carbonyl hydrogenation under subatmospheric to atmospheric hydrogen pressure enabled by robust heterogeneous Pt–Fe catalysts

• Hiroyuki Miyamura,
• Ryosuke Kajiyama,
• Shun-ya Onozawa,
• Yoshihiro Kon and
• Shū Kobayashi

Beilstein J. Org. Chem. 2026, 22, 575–582, doi:10.3762/bjoc.22.43

• ) was converted to the corresponding alcohol 2d in 89% yield under continuous-flow conditions at room temperature (Table 2, entry 3). The desired product 2d was obtained quantitatively at 50 °C (Table 2, entry 4). It is noteworthy that an analytically pure compound (confirmed by 1H and 13C NMR) was

• : Additional experimental details, materials, and methods including photographs of reactor systems, STEM-EDS images and XPS spectra of heterogeneous catalysts, and copies of 1H and 13C NMR spectra for isolated compounds. Acknowledgements H. M. also thanks the Joint Usage/Research Center for Catalysis

Kinetic resolution of racemic planar-chiral vinylcymantrenes by molybdenum-catalyzed asymmetric metathesis dimerization

• Haruna Imazu,
• Hitoshi Izu,
• Yasuhiro Ohki and
• Masamichi Ogasawara

Beilstein J. Org. Chem. 2026, 22, 568–574, doi:10.3762/bjoc.22.42

• reaction at 60 °C for 24 h. The crude reaction mixture was analyzed by 1H NMR measurement, which revealed the presence of the two diastereomers in the dimerized product with the molar ratio of chiral-2a/meso-2a = 97:3. The enantiomeric purity of recovered (S)-1a was determined to be 34% ee, while that of

• substrates rac-1a–c. Molybdenum-catalyzed asymmetric metathesis dimerization/kinetic resolution of racemic vinylcymantrenes 1a–c.a Supporting Information Supporting Information File 19: Experimental procedures, NMR spectra (1H and 13C) for all the new compounds, and chiral HPLC chromatograms. Supporting

Molecular tweezer–peptide conjugates disrupt the protein–protein interaction between survivin and histone H3 essential in mitosis

• Catherine Gsell,
• Philipp Rebmann,
• Karina Opara,
• Christine Beuck,
• Peter Bayer,
• David Bier,
• Ingrid R. Vetter and
• Thomas Schrader

Beilstein J. Org. Chem. 2026, 22, 557–567, doi:10.3762/bjoc.22.41

• various projects with tailored peptide tweezer conjugates: For example, the self-complementary ELTLGEFL sequence of the nuclear export signal in survivin was coupled to tweezers which rendered them selective for this important interface (NMR evidence, 1:1 stoichiometry, K/A mutants) and prevented the

• by computational modeling (MD and QM/MM simulations) as well as structural biology (NMR/X-ray). Following our powerful concept of reinforcing natural peptide–protein interactions by tweezer conjugation [9][10], we envisaged to attach molecular tweezers to the histone H3 terminus at a distance which

• lyophilization, the product 2a was obtained as fully protonated TFA salt (43%); deprotonation with equimolar aq. NaOH produced the sodium salt of 2a quantitatively. The analytical characterization of 2a turned out to be difficult, because even in DMSO-d6, most NMR signals remained very broad, and in part

Experimental and DFT studies on the regioselective methanolysis of 5-azido-9-oxabicyclo[6.1.0]nonan-4-yl 4-nitrobenzoate isomers

• İlknur Polat,
• Selçuk Eşsiz and
• Emine Salamci

Beilstein J. Org. Chem. 2026, 22, 547–556, doi:10.3762/bjoc.22.40

• epoxide ring and acetylation resulted in the formation of two corresponding chloro-acetate isomers. The structure of one of the chloro-acetate isomers was determined via crystallographic analysis and the other by 1D and 2D NMR spectroscopy. DFT computations confirm the regioselectivity of the methanolysis

• ) in pyridine and 4-(dimethylamino)pyridine (DMAP) in 95% yield. Treatment of azido nitrobenzoate 8 with m-CPBA gave a mixture of isomeric epoxides 9a and 9b with a combined yield of 97%. The formation and ratio of these isomers were determined by NMR spectroscopy, showing a 63:37 ratio (1H NMR) of 9a

• intermediate 12 with the anti-face of the benzoate to give compound 14. Similarly, the chloride anion attacks by SN2-type the epoxide ring of intermediate 15 to give the sole product 16. The structure of acetate 11 was investigated using 1D (1H and 13C) and 2D (COSY, NOESY, NOE-diff, and HMQC) NMR

Melifoliox B, a novel phloroglucin derivative isolated from Melicope barbigera (Rutaceae) and synthesis of new oxidation products from melifoliones A and B

• Horst Weber,
• Kim-Thao Tran-Cong,
• Bernhard Mayer,
• Guido J. Reiss,
• Iryna S. Konovalova,
• Marc S. Appelhans,
• Kenneth R. Wood and
• Claus M. Passreiter

Beilstein J. Org. Chem. 2026, 22, 535–546, doi:10.3762/bjoc.22.39

• resolution electrospray ionization mass spectrometry (HRESIMS) and NMR spectra. However, the isomeric compound 3 could not be detected in the extract (Figure 1). Since 4 could be an artefact, built by oxidation of 2 during working up of the extract, and to finally confirm the structure, the isomeric

• diacetate (EDDA). However, synthesis of 2 was difficult. Despite numerous attempts, we only were able to get mixtures of both melifoliones with minor amounts of 2. Since all attempts to separate both isomers on a preparative scale failed, we were only able to record NMR spectra from a very small quantity of

• structure. The 1H NMR spectrum of 4 showed signals for 22 protons (Table 1) with a certain similarity to the melifoliones, but with an exchangeable signal found at δ 2.88 ppm, typical for a tertiary carbinol, instead of a phenolic OH-group at about δ 13 ppm, found in the spectra of the melifoliones. All 18

Get a better glimpse on sequential photoreactions of trisnorbornadienes with ¹⁹F NMR spectroscopy

• Julian Felix Maria Hebborn,
• Ben Eric Merten,
• Thomas Paululat and
• Heiko Ihmels

Beilstein J. Org. Chem. 2026, 22, 527–534, doi:10.3762/bjoc.22.38

• exemplarily with a trifluorinated trisnorbornadienylbenzene that 19F NMR spectroscopy may be applied as a useful complementary method for the investigation of sequential photoreactions. The trisnorbornadiene core structure was used as it figures as promising scaffold for molecular solar thermal (MOST) energy

• trisquadricyclane. Even though the reaction can be monitored by photometry or by in situ 1H NMR spectroscopy, unambiguous assignment of the distinct intermediate mono- and bisquadricyclanes was not possible because of signal overlap. In contrast, this shortcoming is circumvented with in situ 19F NMR-spectroscopic

• analysis. Contrary to the 1H NMR spectra, the 19F NMR spectra show significantly fewer characteristic and sufficiently separated signals that allow the unambiguous identification of all photoproducts and, thus, their detection in the course of the photoreaction. Keywords: fluoroarenes; molecular solar

Synthesis and uranyl(VI) extraction performance of a calix[4]pyrrole–tetrahydroxamic acid receptor

• Sara Karnib,
• Rana Baydoun,
• Wissam Zaidan,
• Nancy AlHaddad,
• Omar El Samad,
• Bilal Nsouli,
• Francine Cazier-Dennin and
• Pierre-Edouard Danjou

Beilstein J. Org. Chem. 2026, 22, 486–494, doi:10.3762/bjoc.22.36

• % yield. Its structure was confirmed by 1H NMR, 13C NMR, and HRMS. The uranium(VI) extraction efficiency of PCP HA was evaluated by solid–liquid extraction experiments, using uranyl acetate as the uranium source, with measurements performed by gamma spectroscopy. PCP HA demonstrated good performance

• using thin-layer chromatography, with the appearance of the characteristic red spot upon treatment with FeCl3 confirming the presence of the hydroxamic acid functionality. Moreover, the formation of the tetra-hydroxamic acid product was confirmed by 1H NMR spectroscopy in deuterated DMSO, as evidenced

• ester substrate. When this method was used, the 1H NMR spectra of the products revealed residual peaks corresponding to unreacted ester (Supporting Information File 1, Figure S8). This observation is consistent with the substrate-dependent behavior reported in that study, highlighting that the reaction

Synthesis of a HDAC inhibitor–nanogold probe for cryo-EM visualization in class I HDAC co-repressor complexes

• Wiktoria A. Pytel,
• John W. R. Schwabe and
• James T. Hodgkinson

Beilstein J. Org. Chem. 2026, 22, 480–485, doi:10.3762/bjoc.22.35

• to its corresponding NHS ester 8 and residual starting material was removed by column chromatography. The Boc-protecting group was removed under anhydrous conditions in good yield and the structure of 9 was confirmed by NMR spectroscopy. Compound 9 was maintained as the TFA salt for the final step

• , and was stable for days stored at −20 °C (stability determined by 1H NMR, Figures S1–S4 in Supporting Information File 1). For the conjugation of 9 to Au–NH2, an excess of 9 was used to drive the conjugation reaction to completion. Unreacted 9 was then removed by repeated washing with water and buffer

• for assistance and guidance in Cryo-EM experiments. We thank Dr. Vanessa M. Timmermann and Dr. Rebecca Hawker for assistance in NMR analysis and Dr. Sharad C. Mistry for assistance in mass spectrometry. Funding We thank the following funders: EPSRC (EP/S030492/1 to JTH; EP/W02151X/1 NMR facility); MRC

Structural reassignment of compound 968, an allosteric glutaminase inhibitor

• Lindsey A. Albertelli,
• Sainabou Jallow,
• Chun Li and
• Scott M. Ulrich

Beilstein J. Org. Chem. 2026, 22, 455–460, doi:10.3762/bjoc.22.33

• anticancer drug target. Compound 968 is a glutaminase inhibitor that is widely used to probe cancer cells’ dependence on glutaminase activity. Here, we show by NMR spectroscopy and X-ray crystallography that the reported benzo[c]phenanthridine structure of compound 968 is incorrect; its true structure is the

• ] and the substrate scope of diketone, arylamine, and arylaldehyde was widened over the subsequent decades [25][26][27]. However, later reports by Martinez et al. [28] using X-ray crystallography and Kozlov et al. [29][30] using NOESY NMR showed that this three-component cyclocondensation reaction does

• reassigning the structure of the cycloaddition reaction product from benzo[c]phenanthridine 1 to benzo[c]acridine 2, we predicted that all three compounds are the benzo[c]acridine isomer 2. The 1H NMR spectra of all three compounds are identical, indicating that they share the same structure (Figure 3A). We

A facile and practical method for the synthesis of trans-(±)-taxifolin and its derivatives via Darzens reaction

• Bo Peng,
• Panpan Yang,
• Maaz Khan,
• Xiaotong Lin,
• Jiang Wu,
• Peng Fu and
• Qingqing Wu

Beilstein J. Org. Chem. 2026, 22, 443–450, doi:10.3762/bjoc.22.31

• moieties (such as bis- or tris-MOMO-substituted phenyl substituents). Due to the steric hindrance, the trans-configured product with the phenyl substituents on the opposite side of the epoxy functionality is obtained. Additionally, the clean reaction process shown by TLC and the NMR spectrum of the product

Synthesis and stereochemical analysis of dynamic planar chiral oxa[7]orthocyclophene

• Yukiho Hashimoto,
• Yuuya Kawasaki,
• Kazunobu Igawa and
• Katsuhiko Tomooka

Beilstein J. Org. Chem. 2026, 22, 436–442, doi:10.3762/bjoc.22.30

• procedures, characterization data, copies of 1H and 13C NMR spectra, and optimized geometries of DFT calculations. Supporting Information File 26: Crystallographic information file of compound 1ac. Acknowledgements We thank K. Imamura (Evaluation center of material properties, IMCE Kyushu University) for

Synthesis and anti-cancer activity of naphthalimide–organylselanyl conjugates

• Rajkumar Ravi and
• Selvakumar Karuthapandi

Beilstein J. Org. Chem. 2026, 22, 416–435, doi:10.3762/bjoc.22.29

• conserved 3-(4-(tert-butyl)phenoxy)propyl function at the imide nitrogen. The resultant naphthalimide–organylselanyl conjugates, NAP-SePh and NAP-Se(n-Oct), were characterised using various spectroscopic techniques, including FTIR, ¹H, ¹³C, ⁷⁷Se NMR and high-resolution mass spectrometry (HRMS). NAP-SePh was

• compounds, making it a viable alternative for introducing long alkyl chains into selenium-containing systems towards lysosomal membrane permeability (vide supra) [42][43][44]. After synthesis, compounds 7 and 8 were thoroughly characterised using multinuclear NMR spectroscopy ¹H, ¹³C, and ⁷⁷Se NMR

• (Supporting Information File 1, S11–S13 and S16–S18). In the ¹H NMR spectrum of compound 7, the tert-butyl protons appeared as a singlet at 1.27 ppm. The protons of the propylene linker chain resonated in the aliphatic region at 2.22, 4.08, and 4.37 ppm. The aromatic protons of the tert-butyl-substituted

Cone p-aminocalix[4]arenes enriched with ‘clickable’ alkyne or azide functionalities

• Ilia Korniltsev,
• Vasily Bazhenov,
• Alexander Gorbunov,
• Dmitry Cheshkov,
• Stanislav Bezzubov,
• Vladimir Kovalev and
• Ivan Vatsouro

Beilstein J. Org. Chem. 2026, 22, 399–415, doi:10.3762/bjoc.22.28

• tetraureacalix[4]arenes was obtained. Examination of the 1H NMR spectra of the tetraureas in CDCl3 showed that in most cases triazole heterocycles do not intervene the formation of homo- and heterodimeric capsules by these compounds. Thus, considering the synthetic value of CuAAC and amine transformations, p

• calix[4]arene 11 having four TBS-protected propargyl groups at the narrow rim in only moderate yield of 37% [9]. In our hands, according to the NMR spectra of the reaction mixture, under the reported conditions (>30 equiv of fuming HNO3 per calixarene aromatic unit in a 1:1 dichloromethane/acetic acid

• mixture, from 0 °C → rt, overnight) the nitration of calixarene 6 resulted in a mixture of exhaustively nitrated product 11, partially nitrated calixarenes having nitro and tert-butyl groups at the wide rims, and a large amount of other calixarene side product(s) having broadened and non-interpretable NMR

Design, synthesis and biological evaluation of 2,5-diaryloxazolo[4,5-d]pyrimidin-7-ylamines as selective cytotoxic agents against HeLa cells

• Maryna V. Kachaeva,
• Agnieszka B. Olejniczak,
• Marta Denel-Bobrowska,
• Victor V. Zhirnov,
• Yevheniia S. Velihina,
• Stepan G. Pilyo and
• Volodymyr S. Brovarets

Beilstein J. Org. Chem. 2026, 22, 390–398, doi:10.3762/bjoc.22.27

• Analytique, Université d’Orléans, Pôle de chimierue de Chartres, BP 6759, 45067 Orléans Cedex 2, France 10.3762/bjoc.22.27 Abstract Nine novel functionalized 2,5-diaryloxazolo[4,5-d]pyrimidin-7-ylamines were designed, synthesized and characterized using 1H, 13C NMR, IR spectroscopy, elemental analysis, and

• cyclocondensation products – [1,3]oxazolo[4,5-d]pyrimidines. Subsequent reaction with phosphoryl chloride in the presence of N,N-dimethylaniline converted these intermediates into 2,5-diaryl-7-chloro[1,3]oxazolo[4,5-d]pyrimidines II. The structures of compounds 1–9 were proven and confirmed by 1H and 13C NMR, IR

• were followed by TLC (Silica gel, aluminum sheets 60 F254, Merck). Melting points were recorded on a Fisher-Johns apparatus. 1H and 13C NMR spectra were recorded on a Varian Mercury spectrometer (400 and 101 MHz, respectively) or Bruker Avance DRX 500 spectrometer (500 MHz and 126 MHz, respectively) in

Dialkylaminoalkylation of β-ketosulfones via ring-opening of 3-sulfonylpyrrolidines

• Evgeny M. Buev,
• Alexander V. Pavlushin,
• Vladimir S. Moshkin and
• Vyacheslav Y. Sosnovskikh

Beilstein J. Org. Chem. 2026, 22, 383–389, doi:10.3762/bjoc.22.26

• modifications and the use of the obtained compounds as building blocks. We also examined other nucleophiles suitable for the described domino-sequence. Thus, application of ethanol as solvent resulted in a mixture of the desired product 4b with the corresponding intermediate C (NMR ratio 88:12), however, longer

Electrosynthetic access to unsymmetrical oxaza[8]helicenes with high chiral stability and strong circularly polarized luminescence (CPL)

• Tin Zar Aye,
• Rubal Sharma,
• Muthu Karuppasamy,
• Daiya Suzuki,
• Haruka Nakajima,
• Yoshitane Imai,
• Mitsuhiro Arisawa,
• Mohamed S. H. Salem and
• Shinobu Takizawa

Beilstein J. Org. Chem. 2026, 22, 372–382, doi:10.3762/bjoc.22.25

• unsymmetrical oxaza[8]helicenes 5. Chiroptical features of oxaza[8]helicenes 5 and oxaza[7]helicenes 6. Supporting Information Supporting Information File 9: Experimental procedures, synthetic details, NMR spectra, chiral HPLC chromatograms, DFT and TD-DFT calculations. Supporting Information File 10

Recent advances in the cleavage of non-activated amides

• Eun-Sol Choi and
• Hyo-Jun Lee

Beilstein J. Org. Chem. 2026, 22, 352–369, doi:10.3762/bjoc.22.23

• 86% yield. Mechanistic studies indicated that the pyrrolidine-based amide 73 reacts with iodonium salt 67 to form an imidate triflate intermediate U, which was isolated and characterized by NMR and HRMS. Subsequent hydrolysis via water attack affords the trifluoroethyl ester. This strategy also

Synthesis of tricyclic fused pyrrolidine nitroxides from 2-alkynylpyrrolidine-1-oxyls

• Mark M. Gulman,
• Yuliya F. Polienko,
• Sofia Yu. Trakhininа,
• Yuri V. Gatilov,
• Tatyana V. Rybalova,
• Sergey A. Dobrynin and
• Igor A. Kirilyuk

Beilstein J. Org. Chem. 2026, 22, 344–351, doi:10.3762/bjoc.22.22

• nitroxides 2d–f, the samples of the radicals were reduced to the corresponding diamagnetic amines using a Zn/CF3COOH system in CD3OD at 63 °C, according to a literature protocol [23] and the 1H NMR spectra were recorded. The spectra showed similarity to those of previously described for radicals 2a–c [20

• sulfonate group, respectively [24]. The 1H NMR spectra of 3a,b,d–f (Zn/CF3COOH system in CD3OD) showed appearance of a singlet of methanesulfonate hydrogens in the region from 2.78 to 3.17 ppm. The NMR spectra were not recorded for 3c because of heavy resinification upon the sample preparation. The

• % yield). The IR spectra of the pyrazole derivatives 9a–c exhibit absorptions at 688–699 cm−1 and 763–770 cm−1, assigned to out-of-plane bending modes of the pyrazole ring [32]. The 1H NMR spectra of the reduction products of pyrazoles 9a–c were recorded after reduction using the Zn/CF3COOH system in

Spirobarbiturates with a pyrrolizidine moiety: synthesis, structure and biological evaluation

• Arthur A. Puzyrkov,
• Andrew S. Drachuk,
• Ekaterina A. Popova,
• Alexander V. Stepakov and
• Vitali M. Boitsov

Beilstein J. Org. Chem. 2026, 22, 274–288, doi:10.3762/bjoc.22.20

• groups at the meta-position of the aromatic ring. In both cases, the endo-isomers predominated among the cycloadducts. However, using an N-arylmaleimide with an ortho-methoxy group, we obtained product 4p (26%) as diastereomeric mixture, and the exo-isomer became the major product. Notably, the 1H NMR

• configuration of their stereocenters, was determined using NMR spectroscopy and XRD analysis. endo-Isomers 4a–e exhibited the following characteristic signals in their 1H NMR spectra: multiplets in the range of δ 1.5–4.4 ppm were assigned to the protons of the pyrrolizidine ring system. The methyl singlets of

• were established using 1H,13C HSQC NMR spectroscopy. The chemical shift values, signal shapes, and spin–spin coupling constants are provided in Table S1 in Supporting Information File 1. The aromatic protons of compounds 4c–e appear in the downfield region of the spectrum. For product 4c, the aromatic