Synthesis and properties of 6-alkynyl-5-aryluracils

• Ruben Manuel Figueira de Abreu,
• Till Brockmann,
• Alexander Villinger,
• Peter Ehlers and
• Peter Langer

Beilstein J. Org. Chem. 2024, 20, 898–911, doi:10.3762/bjoc.20.80

• was performed on Merck Silica gel 60 (particle size 63–200 μm). Solvents for extraction and column chromatography were distilled prior employment. Representative method for the preparation of starting materials 5-Bromo-6-chloro-1,3-dimethyluracil (2). Uracil 1 (22.9 mmol; 4.00 g) was dissolved in

Activity assays of NnlA homologs suggest the natural product N-nitroglycine is degraded by diverse bacteria

• Kara A. Strickland,
• Brenda Martinez Rodriguez,
• Ashley A. Holland,
• Shelby Wagner,
• Michelle Luna-Alva,
• David E. Graham and
• Jonathan D. Caranto

Beilstein J. Org. Chem. 2024, 20, 830–840, doi:10.3762/bjoc.20.75

• band observed in the SDS-PAGE gel of each homolog is consistent with the expected monomer molecular masses of approximately 21 kDa, several other bands appear (Figure 2A). The banding patterns of each of the homologs are similar to those of Vs NnlA. These higher molecular weight bands are likely not

Advancements in hydrochlorination of alkenes

• Daniel S. Müller

Beilstein J. Org. Chem. 2024, 20, 787–814, doi:10.3762/bjoc.20.72

• -workers [10][58]. They observed that silica gel and alumina, when thermally equilibrated (120 °C, 48 h), facilitated efficient hydrochlorinations when treated with HCl or reactive chlorides. A compelling demonstration of the potent role of silica gel is presented in Table 4. In the absence of silica gel

• , cycloheptene (61), when exposed to a concentrated solution of HCl in dichloromethane, did not show any reaction (Table 4, entry 1). Under the same conditions, in the presence of silica gel, they observed 97% conversion and a GC yield of 62% for chloride 62 (Table 4, entry 2). Further optimization identified

• and the surface area of the silica gel or alumina. Ethereal solvents were found to yield hydrochlorination reactions only with highly reactive alkenes, such as pinene. Subsequent studies revealed the need to adapt the hydrochlorination procedure for each substrate (e.g., Table 5). For instance, the

Isolation and structure determination of a new analog of polycavernosides from marine Okeania sp. cyanobacterium

• Kairi Umeda,
• Naoaki Kurisawa,
• Ghulam Jeelani,
• Tomoyoshi Nozaki,
• Kiyotake Suenaga and
• Arihiro Iwasaki

Beilstein J. Org. Chem. 2024, 20, 645–652, doi:10.3762/bjoc.20.57

• hexane. The aqueous MeOH portion was purified by reversed-phase column chromatography (ODS silica gel, MeOH/H2O), automated flash chromatography (hexane/EtOAc), and repeated reversed-phase HPLC to give polycavernoside E (1, 0.5 mg as a colorless oil). The isolation of compound 1 was directed by its

• based on HMBC and HMQC experiments. HRESIMS spectra were obtained on a Bruker timsTOF mass spectrometer. For reversed-phase column chromatography, ODS silica gel Cosmosil 75C18-OPN (Nacalai Tesque) was used. For medium pressure column chromatography, AFCS (Smart Flash AKROS, Yamazen) consisting of a

Chemical and biosynthetic potential of Penicillium shentong XL-F41

• Ran Zou,
• Xin Li,
• Xiaochen Chen,
• Yue-Wei Guo and
• Baofu Xu

Beilstein J. Org. Chem. 2024, 20, 597–606, doi:10.3762/bjoc.20.52

• extract was partitioned between EtOAc and H2O. The EtOAc fraction was chromatographed repeatedly over silica gel and reversed-phase high-performance liquid chromatography (RP-HPLC), resulting in the isolation of pure compounds 1–12 (Figure 2). According to literature reports of known compounds, some of

• IMS Q-Tof liquid chromatograph mass spectrometer. For NMR analysis, we utilized an AVANCE II 600 spectrometer, referencing residual solvent peaks at δH/δC 7.27/77.0 ppm in CDCl3 for chemical shift calibration. We utilized commercial silica gel from Yantai Xinnuo New Material Technology Co., Ltd

• gradient of petroleum ether–ethyl acetate (PE–EA) and ethyl acetate–methanol (EA–MeOH) to yield 22 fractions (Fr.A–Fr.N) as determined by TLC analysis. Fraction Fr.J (62.32 mg) was further purified using silica gel column chromatography with a PE–EtOAc gradient to obtain nine subfractions (Fr.J1–Fr.J9

A myo-inositol dehydrogenase involved in aminocyclitol biosynthesis of hygromycin A

• Michael O. Akintubosun and
• Melanie A. Higgins

Beilstein J. Org. Chem. 2024, 20, 589–596, doi:10.3762/bjoc.20.51

• imidazole in binding buffer (10, 20, 50, and 500 mM imidazole). Fractions were run on an ExpressPlusTM PAGE Gel (GenScript) and protein was visualized using Coomassie Brilliant Blue G-250 (VWR). Fractions containing Hyg17 were pooled and further purified using a HiLoad 16/600 Superdex 75 pg size exclusion

• . Reactions for thin-layer chromatography analysis were carried out using the same general reaction conditions reported above. Six μL of each reaction were spotted on the TLC silica gel 60 F254 (Sigma) and run with a solvent system containing butanol/ethanol/water 5:4:3. The TLC was stained using a solution

Synthesis and biological profile of 2,3-dihydro[1,3]thiazolo[4,5-b]pyridines, a novel class of acyl-ACP thioesterase inhibitors

• Jens Frackenpohl,
• David M. Barber,
• Guido Bojack,
• Birgit Bollenbach-Wahl,
• Ralf Braun,
• Rahel Getachew,
• Sabine Hohmann,
• Kwang-Yoon Ko,
• Karoline Kurowski,
• Bernd Laber,
• Rebecca L. Mattison,
• Thomas Müller,
• Anna M. Reingruber,
• Dirk Schmutzler and
• Andrea Svejda

Beilstein J. Org. Chem. 2024, 20, 540–551, doi:10.3762/bjoc.20.46

• -ynylcarbamoyl)-1,3-dioxolane-2-carboxamide [3] and FAM azide, 5-isomer (Broadpharm BP-22544, San Diego, CA) by click chemistry [29] and was purified by flash column chromatography on silica gel. Preemergence efficacy of 2,3-dihydro[1,3]thiazolo[4,5-b]pyridine-based FAT inhibitors 7b, 7c, and 13b as well as

Switchable molecular tweezers: design and applications

• Pablo Msellem,
• Maksym Dekthiarenko,
• Nihal Hadj Seyd and
• Guillaume Vives

Beilstein J. Org. Chem. 2024, 20, 504–539, doi:10.3762/bjoc.20.45

A new analog of dihydroxybenzoic acid from Saccharopolyspora sp. KR21-0001

• Rattiya Janthanom,
• Yuta Kikuchi,
• Hiroki Kanto,
• Tomoyasu Hirose,
• Arisu Tahara,
• Takahiro Ishii,
• Arinthip Thamchaipenet and
• Yuki Inahashi

Beilstein J. Org. Chem. 2024, 20, 497–503, doi:10.3762/bjoc.20.44

• flowthrough fraction was adjusted to 3 with formic acid (FA) and chromatographed again on HP20 column. Now, 1 was retained in the resin and eluted by 50% MeOH with 0.05% FA. Then 1 was purified by silica gel and ODS column chromatography, and ethyl acetate extraction under acidic conditions. As the result of

• and extracted with ethyl acetate. The ethyl acetate layer was purified using a silica gel column (25 i.d. × 300 mm) by eluting with CHCl3/MeOH (100:0, 100:1, 100:2, 10:1, 1:1, and 0:100). The 10:1 fraction was purified with an ODS column (47 i.d. × 260 mm) by eluting with MeOH/H2O (0%, 10%, 20%, 30

Pseudallenes A and B, new sulfur-containing ovalicin sesquiterpenoid derivatives with antimicrobial activity from the deep-sea cold seep sediment-derived fungus Pseudallescheria boydii CS-793

• Zhen Ying,
• Xiao-Ming Li,
• Sui-Qun Yang,
• Hong-Lei Li,
• Xin Li,
• Bin-Gui Wang and
• Ling-Hong Meng

Beilstein J. Org. Chem. 2024, 20, 470–478, doi:10.3762/bjoc.20.42

• Discussion For chemical investigation, the solvent EtOAc was used to extract the fermentation culture of the fungus P. boydii CS-793 to afford an organic extract. Isolation and purification of the crude extract with a combination of column chromatography (CC) by Lobar LiChroprep RP-18, silica gel, Sephadex

• by Chromeleon software (version 6.80). LC–MS were obtained with a Bruker maXis plus Q-TOF. Column chromatography was carried out using commercially available silica gel (200–300 mesh, Qingdao Haiyang Chemical Co.), Lobar LiChroprep RP-18 (40–63 μm, Merck), and Sephadex LH-20 (Pharmacia). Thin-layer

• chromatography (TLC) was performed with precoated Si gel GF254 plates (Merck, Darmstadt, Germany). Solvents used for extraction and purification were distilled prior to use. Peptone from yeast extract was purchased from Sigma-Aldrich. Rice, monosodium glutamate, and corn steep liquor were purchased from China

Synthesis of 2,2-difluoro-1,3-diketone and 2,2-difluoro-1,3-ketoester derivatives using fluorine gas

• Alexander S. Hampton,
• David R. W. Hodgson,
• Graham McDougald,
• Linhua Wang and
• Graham Sandford

Beilstein J. Org. Chem. 2024, 20, 460–469, doi:10.3762/bjoc.20.41

• difluorinated product 5a in 85% isolated yield. Purification of 5a was achieved very readily by eluting the reaction mixture through a small quantity of silica gel with chloroform and evaporating the residual solvent to leave the crude product which could be further purified by recrystallization. Subsequently

• , a range of ethyl benzoylacetate derivatives was prepared (see Supporting Information File 1) [45][46] and successfully subjected to difluorination conditions (Table 3). Purification by column chromatography using the minimum amount of silica gel with chloroform as the eluent yielded 5c–g in high

Development of a chemical scaffold for inhibiting nonribosomal peptide synthetases in live bacterial cells

• Fumihiro Ishikawa,
• Sho Konno,
• Hideaki Kakeya and
• Genzoh Tanabe

Beilstein J. Org. Chem. 2024, 20, 445–451, doi:10.3762/bjoc.20.39

• benzophenone moiety in probe 3. The samples were then reacted with TAMRA-N3 (structure shown in Figure S4, Supporting Information File 1) under copper(I)-catalyzed azide–alkyne cycloaddition conditions [21] and subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis coupled with in-gel

• 4–9 (100 µM), irradiated at 365 nm, and subjected to the click reaction with TAMRA-N3. In-gel fluorescence scanning revealed that inhibitors 1, 2, 4, and 7 completely suppressed GrsA labeling by probe 3 in the proteomic environment (Figure 4b). Unlike the results obtained for the labeling of

• are treated with a TAMRA-N3 under copper(I)-catalyzed azide–alkyne cycloaddition conditions, followed by SDS-PAGE coupled with in-gel fluorescence scanning. AMS, 5′-O-sulfamoyladenosine. Competitive labeling experiments of GrsA using probe 3 in the presence of ʟ-Phe-AMS inhibitors. (A) Labeling of

Mono or double Pd-catalyzed C–H bond functionalization for the annulative π-extension of 1,8-dibromonaphthalene: a one pot access to fluoranthene derivatives

• Nahed Ketata,
• Linhao Liu,
• Ridha Ben Salem and
• Henri Doucet

Beilstein J. Org. Chem. 2024, 20, 427–435, doi:10.3762/bjoc.20.37

• of PdCl(C3H5)(dppb) (30.5 mg, 0.05 mmol) at 150 °C during 16 h in DMA (4 mL) under argon affords the coupling products 1–18 after evaporation of the solvent and purification on silica gel. Eluent EtOAc/heptane 1:9 for compounds 3–8, 10–18; heptane for compounds 1, 2, and 9. General procedure for the

• DMA (4 mL) under argon affords the coupling products 19–27 after evaporation of the solvent and purification on silica gel. Eluent EtOAc/heptane 1:9 for compounds 19–24; heptane for compounds 25 and 26; EtOAc/heptane 2:8 for compound 27. General procedure for the palladium-catalyzed synthesis of 9

• (4 mL) under argon affords the coupling products 28–30 after evaporation of the solvent and purification on silica gel. Eluent EtOAc/heptane 1:9 for all compounds. Structure of fluoranthene. Pd-catalyzed access to fluoranthenes. Scope of the Pd-catalyzed direct arylation reaction of arenes with 1,8

Green and sustainable approaches for the Friedel–Crafts reaction between aldehydes and indoles

• Periklis X. Kolagkis,
• Eirini M. Galathri and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2024, 20, 379–426, doi:10.3762/bjoc.20.36

• acids, such as N-bromosuccinimide (NBS) [54], silica chloride [55], Ph3CCl [56], ZnO [57], La(NO3)3·6H2O [58], V(HSO4)3 [59], Cu(ClO4)2·6H2O [60], Fe/Al pillared clay [61], trimethylsilyl chloride (TMSCl) [62], BiCl3-loaded montmorillonite K10 [63][64][65][66][67], ZrO2-MgO [68] or CaO [69]. Silica gel

• , Rahimizadeh et al. proposed the use of the nanometal oxide TiO2, which was already reported as an effective nanocatalyst for the promotion of various organic transformations [100]. TiO2 nanoparticles are non-toxic, inexpensive and reusable compounds that are synthesized through a sol–gel method. This method

• nanocatalyst utilized and a more restricted substrate scope [104]. Karthikeyan and his research team synthesized Ag-Pt nanoparticles suspended in silicate, with the sol–gel method analyzed before, to test their effectiveness in the synthesis of BIMs, since they had already been applied as nanocatalysts in

Elucidating the glycan-binding specificity and structure of Cucumis melo agglutinin, a new R-type lectin

• Jon Lundstrøm,
• Emilie Gillon,
• Valérie Chazalet,
• Nicole Kerekes,
• Antonio Di Maio,
• Ten Feizi,
• Yan Liu,
• Annabelle Varrot and
• Daniel Bojar

Beilstein J. Org. Chem. 2024, 20, 306–320, doi:10.3762/bjoc.20.31

• polymerase (Takara #TAKR045A); then the product was digested by DpnI and finally transformed in NEB5α strain (New England Biolabs, #C2992H). Both gene and vector were digested by NcoI and XhoI restriction enzymes (New England Biolabs) prior to purification on agarose gel using Monarch Gel extraction kit and

• , Merck, #56749) to remove all contaminants and unbound proteins. CMA1 was eluted by a 20 mL linear gradient from 50 mM to 500 mM imidazole in buffer A. The fractions were analyzed by SDS-PAGE with 15% gel and those containing CMA1 were collected and deprived of imidazole by buffer exchange in buffer A

Additive-controlled chemoselective inter-/intramolecular hydroamination via electrochemical PCET process

• Kazuhiro Okamoto,
• Naoki Shida and
• Mahito Atobe

Beilstein J. Org. Chem. 2024, 20, 264–271, doi:10.3762/bjoc.20.27

• of 5 mA (3 F/mol, 57.9 C) through the CF anode (1 × 1 cm) and the Pt cathode (1 × 1 cm). The reaction mixture was concentrated in vacuo and Et2O (20 mL) was added. The resulting precipitate was removed by filtration through a short silica gel pad under reduced pressure. The filtrate was concentrated

• was removed by filtration through a short silica gel pad under reduced pressure. The filtrate was concentrated in vacuo and the resulting residue was subjected to 1H NMR spectroscopy or column chromatography. Application of amidyl radical species generated by PCET. (A) Effect of phosphate base on the

Chiral phosphoric acid-catalyzed transfer hydrogenation of 3,3-difluoro-3H-indoles

• Yumei Wang,
• Guangzhu Wang,
• Yanping Zhu and
• Kaiwu Dong

Beilstein J. Org. Chem. 2024, 20, 205–211, doi:10.3762/bjoc.20.20

• and the reaction mixture was stirred at room temperature for 3 h. After concentrating the mixture, the residue was purified by column chromatography on silica gel using a mixture of petroleum ether/ethyl acetate 30:1 (v/v) as the eluent to afford products 2. The yields were determined by 19F NMR

Comparison of glycosyl donors: a supramer approach

• Anna V. Orlova,
• Nelly N. Malysheva,
• Maria V. Panova,
• Nikita M. Podvalnyy,
• Michael G. Medvedev and
• Leonid O. Kononov

Beilstein J. Org. Chem. 2024, 20, 181–192, doi:10.3762/bjoc.20.18

• the stereoselectivity of sialylation, it is important to analyze anomeric ratio values (α/β) for the disaccharide fraction separated by size-exclusion chromatography since the retention values of different disaccharide anomers on silica gel may be surprisingly large and a minor isomer may be lost

• during purification by silica gel chromatography. On the other hand, NMR analysis of the crude reaction mixtures may be misleading due to possible overlap of the signals of H-3eq belonging both to disaccharide and monosaccharide derivatives sometimes present in such glycosylation mixtures. At low

• glycosylation reactions was distilled under argon over P2O5 and then over CaH2 and stored over molecular sieves (MS) 3 Å. Powdered MS 3 Å (Fluka) were activated before the reactions by heating at ≈220 °C in high vacuum for 6 h. Column chromatography was performed on silica gel 60 (40–63 μm, Merck). Gel

Synthesis of the 3’-O-sulfated TF antigen with a TEG-N₃ linker for glycodendrimersomes preparation to study lectin binding

• Mark Reihill,
• Hanyue Ma,
• Dennis Bengtsson and
• Stefan Oscarson

Beilstein J. Org. Chem. 2024, 20, 173–180, doi:10.3762/bjoc.20.17

• silica gel 60 F254. Visualisation was performed with UV-light (254 nm) fluorescence quenching, and/or by staining with an 8% H2SO4 dip (stock solution: 8 mL conc. H2SO4, 92 mL EtOH), ninhydrin dip (stock solution: 0.3 g ninhydrin, 3 mL AcOH, 100 mL EtOH) and/or ceric ammonium molybdate dip (stock

• solution: 25 g ammonium molybdate tetrahydrate, 0.5 g Ce(SO4)2, 50 mL H2SO4, 450 mL EtOH). Chromatography Silica gel flash chromatography was carried out using Davisil® LC60A (40–63 μm) silica gel or with automated flash chromatography systems, Buchi Reveleris® X2 (UV 200–500 nm and ELSD detection

• Celite® and concentrated in vacuo. The resulting residue was taken up in EtOAc (700 mL) and washed with 10% aq Na2S2O3 (700 mL), water (700 mL) and brine (700 mL). The organic phase was then dried over MgSO4, filtered and reduced to dryness. Flash chromatography on silica gel (toluene→toluene/EtOAc, 3:2

Perspectives on push–pull chromophores derived from click-type [2 + 2] cycloaddition–retroelectrocyclization reactions of electron-rich alkynes and electron-deficient alkenes

• Michio Yamada

Beilstein J. Org. Chem. 2024, 20, 125–154, doi:10.3762/bjoc.20.13

• ) affords 7 with 16% yield, 8 with 25% yield, and 9 with 46% yield. Furthermore, 7 and 8 are efficiently converted into 10 and 11, respectively, with high yields (80% and 95%, respectively) via column chromatography employing silica gel in acetonitrile, thereby instigating further molecular transformation

• surfactant, Brij 30, was used as the reaction solvent at a concentration of 20 mM, exceeding the critical micelle concentration, 4 and 37 were obtained in a ratio of 53:47, with 64% yield. Notably, 37 exhibits instability in silica gel and polar solvents. In particular, when 37 is kept in ethyl acetate or

Photoinduced in situ generation of DNA-targeting ligands: DNA-binding and DNA-photodamaging properties of benzo[c]quinolizinium ions

• Julika Schlosser,
• Olga Fedorova,
• Yuri Fedorov and
• Heiko Ihmels

Beilstein J. Org. Chem. 2024, 20, 101–117, doi:10.3762/bjoc.20.11

• (Table 2). To assess the optimal parameters for the photoreaction, the ligand was irradiated in the presence of the DNA under anaerobic conditions at different irradiation times and concentrations of the ligand. The DNA-strand cleavage was analyzed by agarose-gel electrophoresis. In this assay, the DNA

• ]quinolizinium ions 3b–g (yields in % refer to isolated products). Proposed mechanisms for the photoinduced DNA damage initiated by photoexcitation of benzoquinolizinium 3f. Absorption and emission maxima of 3c–g in the absence and presence of ct DNA and binding constants of their complexes with ct DNA. Gel

Multi-redox indenofluorene chromophores incorporating dithiafulvene donor and ene/enediyne acceptor units

• Christina Schøttler,
• Kasper Lund-Rasmussen,
• Line Broløs,
• Philip Vinterberg,
• Ema Bazikova,
• Viktor B. R. Pedersen and
• Mogens Brøndsted Nielsen

Beilstein J. Org. Chem. 2024, 20, 59–73, doi:10.3762/bjoc.20.8

• molecular sieves, or by drying over 3 Å molecular sieves. All remaining anhydrous solvents were obtained from a solvent drying tower (IT model PS-MD-05). HPLC grade solvents were used unless otherwise specified. Purification by chromatography was performed using silica gel (flash: 40–63 μm, Sepacore® Flash

• Systems X10/X50: 40–63 μm). TLC was performed using aluminum sheets covered with silica gel coated with fluorescent indicator. NMR spectra were recorded on a Bruker instrument at 500 MHz and 126 MHz for 1H and 13C NMR, respectively. Deuterated chloroform (CDCl3, 1H = 7.26 ppm, 13C = 77.16 ppm), deuterated

Identification of the p-coumaric acid biosynthetic gene cluster in Kutzneria albida: insights into the diazotization-dependent deamination pathway

• Seiji Kawai,
• Akito Yamada,
• Yohei Katsuyama and
• Yasuo Ohnishi

Beilstein J. Org. Chem. 2024, 20, 1–11, doi:10.3762/bjoc.20.1

• (15 mg/L) was added to the culture, and the culture was continued for another 1 day. The pH was adjusted to 4 by adding 6 M HCl to the culture, and the metabolites were extracted by ethyl acetate. After the ethyl acetate was evaporated, the metabolites were absorbed for 5.0 g silica gel 60 (0.040

• –0.063 mm, Merck Millipore, Burlington, MA, USA). The silica gel holding the metabolites was applied to a normal-phase medium-pressure liquid chromatography system (MPLC, Shoko Scientific, Kanagawa, Japan) equipped with a silica column (Purif-Pack, Shoko Scientific), and the metabolites were eluted with

Long oligodeoxynucleotides: chemical synthesis, isolation via catching-by-polymerization, verification via sequencing, and gene expression demonstration

• Yipeng Yin,
• Reed Arneson,
• Alexander Apostle,
• Adikari M. D. N. Eriyagama,
• Komal Chillar,
• Emma Burke,
• Martina Jahfetson,
• Yinan Yuan and
• Shiyue Fang

Beilstein J. Org. Chem. 2023, 19, 1957–1965, doi:10.3762/bjoc.19.146

• failure sequences 4 and other impurities were then washed away using aqueous solutions including mildly basic solutions. These washes might also remove N,N-dimethylacrylamide added to ODNs via Michael addition. The full-length ODN 6 was cleaved from the polyacrylamide gel (5) using 80% acetic acid (Scheme

•  1). Because depurination is less likely for deprotected ODNs, and the conditions are widely used for detritylation after RP HPLC, ODN damage in this step is unlikely or negligible. The purified ODNs, 399 and 401 nt, were each extracted from their gel. To remove residual acetic acid, the ODNs were

• dissolved in water and precipitated with n-BuOH. This gave the CBP-purified ODNs. Analysis of long ODNs with gel electrophoresis and Sanger sequencing One simple method to estimate the length of the long ODNs would be to compare them with authentic samples using gel electrophoresis. However, commercial

Aromatic systems with two and three pyridine-2,6-dicarbazolyl-3,5-dicarbonitrile fragments as electron-transporting organic semiconductors exhibiting long-lived emissions

• Karolis Leitonas,
• Brigita Vigante,
• Dmytro Volyniuk,
• Audrius Bucinskas,
• Pavels Dimitrijevs,
• Sindija Lapcinska,
• Pavel Arsenyan and
• Juozas Vidas Grazulevicius

Beilstein J. Org. Chem. 2023, 19, 1867–1880, doi:10.3762/bjoc.19.139

• purification. Thin-layer chromatography (TLC) was performed using Merck Silica gel 60 F254 plates and visualized by UV (254 nm) fluorescence. Zeochem silica gel (ZEOprep 60/35–70 microns – SI23501) was used for column chromatography. 1H and 13C NMR spectra were recorded on a Bruker 400 spectrometer at 400 and

• for 1 h. After cooling, the reaction was quenched by the addition of ice and the precipitate was filtered off. The crude product was purified by flash chromatography on silica gel using chloroform as eluent yielding compound 3 (1.0 g, 78%) as white powder. Mp > 200 °C; 1H NMR (400 MHz, DMSO-d6) 7.91

• dried over Na2SO4. After the solvent was removed, the crude yellow product was carefully washed twice with acetonitrile to remove the starting materials. Further purification was achieved using flash chromatography on silica gel (eluent: dichloromethane/petroleum ether 1:2). Compound 4 (0.86 g, 61%) was