Tenacibactins K–M, cytotoxic siderophores from a coral-associated gliding bacterium of the genus Tenacibaculum

• Yasuhiro Igarashi,
• Yiwei Ge,
• Tao Zhou,
• Amit Raj Sharma,
• Enjuro Harunari,
• Naoya Oku and
• Agus Trianto

Beilstein J. Org. Chem. 2022, 18, 110–119, doi:10.3762/bjoc.18.12

• separated from the aqueous layer containing the mycelium. Evaporation of the solvent gave 6.54 g of extract from 3 L of culture. The extract (6.54 g) was subjected to silica gel column chromatography with a step gradient of CHCl3/MeOH 1:0, 20:1, 10:1, 4:1, 2:1, 1:1, and 0:1 (v/v). Fraction 4 (4:1) was

Efficient and regioselective synthesis of dihydroxy-substituted 2-aminocyclooctane-1-carboxylic acid and its bicyclic derivatives

• İlknur Polat,
• Selçuk Eşsiz,
• Uğur Bozkaya and
• Emine Salamci

Beilstein J. Org. Chem. 2022, 18, 77–85, doi:10.3762/bjoc.18.7

• a mixture of products 10 and 11 in a 7:3 ratio was determined by NMR spectroscopy. The reaction mixture was purified using preparative silica gel TLC on a chromatotron with ethyl acetate/hexane (50:50) as the eluent to give carbamate 10 and diol isomer mixture 11 in 65% and 25% yields, respectively

• (Figure 2) [28]. The formation of lactone 10 can again be explained by participation of the neighbouring group, as discussed above. However, during the purification on silica gel of the lactone-Boc product, its transesterification also resulted in corresponding methyl carbamate 10. We then investigated

Efficient synthesis of ethyl 2-(oxazolin-2-yl)alkanoates via ethoxycarbonylketene-induced electrophilic ring expansion of aziridines

• Yelong Lei and
• Jiaxi Xu

Beilstein J. Org. Chem. 2022, 18, 70–76, doi:10.3762/bjoc.18.6

• , MeCN, and 1,4-dioxane were refluxed over CaH2; toluene was refluxed over Na with benzophenone as an indicator, and all solvents were freshly distilled prior to use. Flash column chromatography was performed using silica gel (normal phase, 200–300 mesh) from Branch of Qingdao Haiyang Chemical. Petroleum

• ether (PE) used for column chromatography was the 60–90 °C fraction, and the removal of residual solvent was accomplished under rotovap. Reactions were monitored by thin-layer chromatography on silica gel GF254 coated 0.2 mm plates from Institute of Yantai Chemical Industry. Microwave-assisted reactions

• (0.36 mmol) and aziridine 2 (0.30 mmol) were added to DCE (1.0 mL) in a sealed 10 mL microwave tube. The resulting solution was stirred at 130 °C for 20 min under microwave heating. After the reaction was completed, the resulting mixture was evaporated in vacuo. The crude residue was purified by silica

Bifunctional thiourea-catalyzed asymmetric [3 + 2] annulation reactions of 2-isothiocyanato-1-indanones with barbiturate-based olefins

• Jiang-Song Zhai and
• Da-Ming Du

Beilstein J. Org. Chem. 2022, 18, 25–36, doi:10.3762/bjoc.18.3

• silica gel (200–300 mesh). Melting points were determined with an XT-4 melting-point apparatus and are uncorrected. 1H NMR spectra were measured with a Bruker Ascend 400 MHz spectrometer, chemical shifts are reported in δ (ppm) units relative to tetramethylsilane (TMS) as an internal standard. 13C NMR

• 1 (0.06 mmol), 2 (0.05 mmol), Et3N (1.0 mg, 0.01 mmol, 0.2 equiv), and DCM (1.0 mL). The mixture was stirred at room temperature for 12 h, then the reaction mixture was concentrated and directly purified by silica gel column chromatography to afford the racemates of 3. 2. Procedure for the synthesis

• of chiral compounds 3 To a dried small bottle were added 1 (0.12 mmol), 2 (0.10 mmol), chiral organocatalyst C4 (2.7 mg, 0.005 mmol, 5 mol %), and DCM (1.0 mL). The mixture was stirred at room temperature for 12‒40 h, then the reaction mixture was concentrated and directly purified by silica gel

Unsaturated fatty acids and a prenylated tryptophan derivative from a rare actinomycete of the genus Couchioplanes

• Shun Saito,
• Kanji Indo,
• Naoya Oku,
• Hisayuki Komaki,
• Masashi Kawasaki and
• Yasuhiro Igarashi

Beilstein J. Org. Chem. 2021, 17, 2939–2949, doi:10.3762/bjoc.17.203

• extracted with 1-butanol. The extract (4.4 g from 3 L) was sequentially fractionated by column chromatographies on silica gel and ODS, and the resulting fractions were purified by reverse-phase HPLC to give 1 (5.2 mg), 2 (2.3 mg), 3 (1.0 mg), 4 (6.3 mg), and 5 (8.0 mg). The molecular formula of 1 was

• between the diastereomer pairs. The enantiomer ratio of 4 was estimated to be S/R = 56:44 or near by chiral phase HPLC analysis of 4' on a cellulose tribenzoate-coated silica gel column (Figure 4). Thus, 4 was concluded to be an enantiomeric mixture of (2E,4E)-7-hydroxy-2,4-dimethyl-2,4-octadienoic acid

• recorded on a Bruker micrOTOF spectrometer. Silica gel 60 (spherical) (Kanto Chemical Co., Inc.) was used for silica gel column chromatography. Cosmosil 75C18-PREP (Nacalai Tesque, Inc.) was used for ODS column chromatography. Routine HPLC separations were performed on an Agilent HP1200 system, and chiral

First total synthesis of hoshinoamide A

• Haipin Zhou,
• Zihan Rui,
• Yiming Yang,
• Shengtao Xu,
• Yutian Shao and
• Long Liu

Beilstein J. Org. Chem. 2021, 17, 2924–2931, doi:10.3762/bjoc.17.201

• 2-chlorotrityl chloride (CTC) resin with 8 (4 equiv) and DIPEA successfully produced the resin-bound tripeptide 3 in good yield [17]. It should be noted that unreacted 8 can be largely recovered by a quick silica gel chromatography. The N terminus of 3 was then sequentially extended with properly

A two-phase bromination process using tetraalkylammonium hydroxide for the practical synthesis of α-bromolactones from lactones

• Yuki Yamamoto,
• Akihiro Tabuchi,
• Kazumi Hosono,
• Takanori Ochi,
• Kento Yamazaki,
• Shintaro Kodama,
• Akihiro Nomoto and
• Akiya Ogawa

Beilstein J. Org. Chem. 2021, 17, 2906–2914, doi:10.3762/bjoc.17.198

• layer was washed with H2O (10 mL × 2), dried by anhydrous Na2SO4, then filtered. The filtrate was concentrated under reduced pressure. Finally, the residue was purified by silica-gel column chromatography (AcOMe/isohexane) to give pure product 5. One-pot synthesis of a functional lactone 6 using PhS−Na

• concentrated under reduced pressure. Finally, the residue was purified by silica-gel column chromatography (Et2O/isohexane) to give pure product 6. General procedure for α-bromination of δ-valerolactone (1a) and the method described in this work. Tetraalkylammonium salt-mediated intramolecular cyclization of

Selective sulfonylation and isonitrilation of para-quinone methides employing TosMIC as a source of sulfonyl group or isonitrile group

• Chuanhua Qu,
• Run Huang,
• Yong Li,
• Tong Liu,
• Yuan Chen and
• Guiting Song

Beilstein J. Org. Chem. 2021, 17, 2822–2831, doi:10.3762/bjoc.17.193

• the reaction mixture was heated under microwave irradiation at 90 °C for 10 min and monitored by TLC until starting material was consumed. Then, the reaction mixture was concentrated under reduced pressure followed by column chromatography over silica gel using petroleum/EtOAc (0 to 10%) as eluent to

• mixture was stirred at 80 °C for 10 h and monitored by TLC. Then, the reaction mixture was concentrated under reduced pressure followed by column chromatography over silica gel using petroleum/EtOAc 10:1 to ≈5:1 as eluent to afford the desired product 4. Selected bioactive compounds. Crystal structure of

Biological properties and conformational studies of amphiphilic Pd(II) and Ni(II) complexes bearing functionalized aroylaminocarbo-N-thioylpyrrolinate units

• Samet Poyraz,
• Samet Belveren,
• Sabriye Aydınoğlu,
• Mahmut Ulger,
• Abel de Cózar,
• Maria de Gracia Retamosa,
• Jose M. Sansano and
• H. Ali Döndaş

Beilstein J. Org. Chem. 2021, 17, 2812–2821, doi:10.3762/bjoc.17.192

• silica gel 60 (230–400 mesh). Kieselgel columns were packed with silica gel GF254 (Merck 7730). Flash chromatography was carried out on handpacked columns of Merck silica gel 60 (0.040–0.063 mm). Melting points were determined on a Stuart SMP3 hot stage apparatus. The structurally most important peaks of

Highly stereocontrolled total synthesis of racemic codonopsinol B through isoxazolidine-4,5-diol vinylation

• Lukáš Ďurina,
• Anna Ďurinová,
• František Trejtnar,
• Ľuboš Janotka,
• Lucia Messingerová,
• Jana Doháňošová,
• Ján Moncol and
• Róbert Fischer

Beilstein J. Org. Chem. 2021, 17, 2781–2786, doi:10.3762/bjoc.17.188

• the proline catalysis are of higher purity (after purification by silica gel column chromatography), than those synthesized by other methods [16]. Definitely, the effective asymmetric organocatalytic conjugate additions of hydroxylamines to enals using various catalysts provide access to

The ethoxycarbonyl group as both activating and protective group in N-acyl-Pictet–Spengler reactions using methoxystyrenes. A short approach to racemic 1-benzyltetrahydroisoquinoline alkaloids

• Marco Keller,
• Karl Sauvageot-Witzku,
• Franz Geisslinger,
• Nicole Urban,
• Michael Schaefer,
• Karin Bartel and
• Franz Bracher

Beilstein J. Org. Chem. 2021, 17, 2716–2725, doi:10.3762/bjoc.17.183

• performed on Merck silica gel Si 60 (0.015–0.040 mm). NMR spectra (1H, 13C, DEPT, H,H-COSY, HSQC, HMQC, HMBC) were recorded at 23 °C on an Avance III 400 MHz Bruker BioSpin or Avance III 500 MHz Bruker BioSpin instrument. Chemical shifts δ are stated in parts per million (ppm) and are calibrated using

Synthetic strategies toward 1,3-oxathiolane nucleoside analogues

• Umesh P. Aher,
• Dhananjai Srivastava,
• Girij P. Singh and
• Jayashree B. S

Beilstein J. Org. Chem. 2021, 17, 2680–2715, doi:10.3762/bjoc.17.182

• diastereomers by silica gel column chromatography and reaction with lead tetraacetate provided the key oxathiolane derivative 31. In 1995, Jin et al. [46] carried out the reaction of 1,4-dithiane-2,5-diol (3q) with glyoxylic acid (3g) hydrate at reflux temperature in tert-butyl methyl ether, which provided the

• . [40] described coupling of crude 1,3-oxathiolane precursor 20 with silylated acetylcytosine utilizing TMSOTf as a Lewis acid, which gave a mixture of α- and β-anomers (1:2 ratio) of 81 (Scheme 30). The mixture of anomers was further separated by silica gel column chromatography. (+)-BCH-189 (1a) and

Ligand-dependent stereoselective Suzuki–Miyaura cross-coupling reactions of β-enamido triflates

• Tomáš Chvojka,
• Athanasios Markos,
• Svatava Voltrová,
• Radek Pohl and
• Petr Beier

Beilstein J. Org. Chem. 2021, 17, 2657–2662, doi:10.3762/bjoc.17.179

• study. Substituted phenylboronic acids and vinyl triflates led to the formation of enamides 2 with high stereoselectivity and in good to high NMR yields (Scheme 2). However, isolated yields were found to be lower due to the decomposition of the formed enamides 2 during column chromatography on silica

• gel. A moderate loss of stereochemistry was observed only in cases of bulky ortho-substitution of either arylboronic acid or vinyl triflate (2ad, 2da, and 2dd). Alkylboronic acids were found to be unreactive even after prolonged reaction time (1a with n-hexylboronic acid, 60 h, rt). Next, conditions

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

• solution of NaHCO3 (3 × 40 mL), dried over Na2SO4, and concentrated under reduced pressure. The residue was purified by column chromatography on silica gel (eluent, hexane/ethyl actate 7:1→5:1), affording the product as dark orange oil in 86% yield. Rf 0.5 (hexane/EtOAc 3:1); IR (ATR): 2971, 2089, 1390

• 30 min. The resulting mixture was concentrated in vacuo and the desired product was isolated by column chromatography on silica gel (EtOAc/MeOH/NH4OH 60:1:0.6→50:1:0.5). (S)-tert-Butyl 2-((3-((R)-tert-butylsulfinyl)thioureido)methyl)pyrrolidine-1-carboxylate ((S,R)-5a) −87.8 (c 1.0, MeOH); 1H NMR

• chromatography on silica gel (EtOAc/MeOH/NH4OH 60:1:0.6→50:1:0.5). (S)-tert-Butyl 2-((3-((R)-tert-butylsulfinyl)ureido)methyl)pyrrolidine-1-carboxylate ((S,R)-5b) −87.3 (c 0.5, MeOH); 1H NMR (600 MHz, CDCl3) δ 9.22 (s, 1H), 6.96 (s, 1H), 4.17–4.09 (m, 1H), 3.76–3.67 (m, 1H), 3.49–3.38 (m, 2H), 3.36–3.31 (m, 1H

α-Ketol and α-iminol rearrangements in synthetic organic and biosynthetic reactions

• Scott Benz and
• Andrew S. Murkin

Beilstein J. Org. Chem. 2021, 17, 2570–2584, doi:10.3762/bjoc.17.172

• ) [13]. Interestingly, when this mixture was subjected to silica gel chromatography, not only could the isomers of 38 not be separated, they also underwent silica-catalyzed α-ketol rearrangement to cyclobutane 39. This rearrangement, however, was of no consequence because addition of sodium methoxide to

• -toluenesulfonic acid), five different Lewis acids (Zn(OTf)2, Cu(OTf)2, Sc(OTf)2, silica gel, and montmorillonite K 10), and one base (NaOEt). Of these, silica gel and montmorillonite K 10 had the best yields (95% and 100%, respectively). A substrate scope was then determined for 97 using aryl, n-hexyl, and

• cyclohexyl R groups in the presence of silica gel at 80 °C (Figure 19b). The rearrangements proceeded well with electron-rich aryl groups, regardless of the position of substitution, but the reaction was especially slow for the electron-withdrawing para-trifluoromethyl derivative. A major advantage of the

Silica gel and microwave-promoted synthesis of dihydropyrrolizines and tetrahydroindolizines from enaminones

• Robin Klintworth,
• Garreth L. Morgans,
• Stefania M. Scalzullo,
• Charles B. de Koning,
• Willem A. L. van Otterlo and
• Joseph P. Michael

Beilstein J. Org. Chem. 2021, 17, 2543–2552, doi:10.3762/bjoc.17.170

• , underwent cyclization in the presence of silica gel to give ethyl 6-(hetero)aryl-2,3-dihydro-1H-pyrrolizine-5-carboxylates within minutes upon microwave heating in xylene at 150 °C. Instead of functioning as a nucleophile, the enaminone acted as an electrophile at its carbonyl group during the cyclization

• temperature and microwave power, although requiring much longer time. A possible mechanism for the cyclization is presented, and further functionalization of the newly created pyrrole ring in the dihydropyrrolizine core is described. Keywords: dihydropyrrolizines; enaminones; microwaves; silica gel

• vinylogous amides such as 11, however, we fortuitously found substituted 2,3-dihydro-1H-pyrrolizines 12 as unexpected products when intermediates 11 were exposed to acidic conditions, including treatment with acetic acid or even during chromatography on silica gel (Scheme 1) [18]. In these cyclizations the

Direct C(sp³)–H allylation of 2-alkylpyridines with Morita–Baylis–Hillman carbonates via a tandem nucleophilic substitution/aza-Cope rearrangement

• Siyu Wang,
• Lianyou Zheng,
• Shutao Wang,
• Shulin Ning,
• Zhuoqi Zhang and
• Jinbao Xiang

Beilstein J. Org. Chem. 2021, 17, 2505–2510, doi:10.3762/bjoc.17.167

• gel column chromatography. EWG = electron withdrawing group. Scope of 2-alkylpyridine 1 with MBH carbonate 2a. The reactions were performed using 1 (1.0 mmol, 2 equiv) and MBH carbonate 2 (0.5 mmol, 1 equiv) in CH3CN (2 mL) at 80 °C unless indicated otherwise. Yields are determined after silica gel

• -alkylpyridines. Mechanistic hypothesis of the alkylation reaction of 2-alkylpyridines with MBH carbonates. Scope of MBH carbonates 2 with 2-picoline 1a. The reactions were performed using 1a (1.0 mmol, 2 equiv) and MBH carbonate 2 (0.5 mmol, 1 equiv) in CH3CN (2 mL) at 80 °C. Yields are determined after silica

Synthesis and investigation on optical and electrochemical properties of 2,4-diaryl-9-chloro-5,6,7,8-tetrahydroacridines

• Najeh Tka,
• Mohamed Adnene Hadj Ayed,
• Mourad Ben Braiek,
• Mahjoub Jabli and
• Peter Langer

Beilstein J. Org. Chem. 2021, 17, 2450–2461, doi:10.3762/bjoc.17.162

• -layer chromatography (TLC). Organic compounds were purified using commercial Merck silica gel (0.043–0.06 mm) with a fluorescence indicator (the visualization was performed under UV light at 254 nm). All solvents for work-up and column chromatography were distilled before use. NMR data were recorded in

Synthesis of 5-arylacetylenyl-1,2,4-oxadiazoles and their transformations under superelectrophilic activation conditions

• Andrey I. Puzanov,
• Dmitry S. Ryabukhin,
• Anna S. Zalivatskaya,
• Dmitriy N. Zakusilo,
• Darya S. Mikson,
• Irina A. Boyarskaya and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2021, 17, 2417–2424, doi:10.3762/bjoc.17.158

• Information File 1). It should be noted that attempts of chromatographic separation of triflates 4a–c into individual E- and Z-isomers on silica gel led to a decrease of their yields and a change in E/Z-ratio. That reveals instability of these compounds on silica gel. In the same reaction in H2SO4 (Scheme 4

Synthesis of phenanthridines via a novel photochemically-mediated cyclization and application to the synthesis of triphaeridine

• Songeziwe Ntsimango,
• Kennedy J. Ngwira,
• Moira L. Bode and
• Charles B. de Koning

Beilstein J. Org. Chem. 2021, 17, 2340–2347, doi:10.3762/bjoc.17.152

• solvent was removed under reduced pressure and the resulting crude biaryl carbonyls were purified using silica gel column chromatography (using EtOAc/hexane mixtures as eluent). Experimental details for the preparation of compounds 13a–f can be found in Supporting Information File 1. Oxime ester formation

• saturated NaHCO3 solution (10 mL) and brine (10 mL). The solution was dried over MgSO4 and the solvent was evaporated under reduced pressure. The resulting crude oxime esters were purified by silica gel column chromatography (using EtOAc/hexane mixtures as eluent). Experimental details for the preparation

• (450 W medium pressure Hg lamp, through a quartz filter) for 3 h. The crude residue was purified by silica gel column chromatography (using EtOAc/hexane mixtures as eluent). Experimental details for the preparation of compounds 15a–d and 16a–f as well as compounds 23 and 24 can be found in Supporting

Phenolic constituents from twigs of Aleurites fordii and their biological activities

• Kyoung Jin Park,
• Won Se Suh,
• Da Hye Yoon,
• Chung Sub Kim,
• Sun Yeou Kim and
• Kang Ro Lee

Beilstein J. Org. Chem. 2021, 17, 2329–2339, doi:10.3762/bjoc.17.151

• SYNAPT G2 mass spectrometer and semipreparative HPLC was conducted using a Gilson 306 pump with a Shodex refractive index detector and a Phenomenex Luna 10 μm column (250 × 10 mm). Silica gel 60 (Merck, Darmstadt, 70–230 mesh, and 230–400 mesh) and RP-C18 silica gel (Merck, 230–400 mesh) were used for

• column chromatography. Low-pressure liquid chromatography was performed over Merck LiChroprep Lobar-A Si gel 60 (240 × 10 mm) with an FMI QSY-0 pump (ISCO). Merck precoated silica gel F254 plates and RP-18 F254s plates were used for TLC. Spots were detected on TLC under UV light or by heating after

• –C6). Fraction C1 (2.0 g) was subjected to RP-C18 silica gel chromatography, eluting with gradient solvent system (30 → 100% aq. MeOH) to yield four subfractions (C2A–C2D). Fraction C2C (210 mg) was purified by semipreparative HPLC (2 mL/min, 50% aq. MeOH) to yield compounds 17 (5 mg) and 19 (6 mg

Synthesis of O⁶-alkylated preQ₁ derivatives

• Laurin Flemmich,
• Sarah Moreno and
• Ronald Micura

Beilstein J. Org. Chem. 2021, 17, 2295–2301, doi:10.3762/bjoc.17.147

• chromatography (TLC) was performed on Marchery-Nagel Polygram SIL G/UV254 plates. Column chromatography was done on silica gel 60 (70–230 mesh). 1H, and 13C NMR spectra were recorded on Bruker DRX 300 MHz, Bruker Avance 4 Neo 400 MHz, and Bruker Avance 4 Neo 700 MHz instruments. Chemical shifts (δ) are reported

• . Compound 3 [29][30][31] (200 mg, 0.720 mmol) was added and the mixture was heated to 110 °C in a pressure tube for 24 h. After neutralization with glacial acetic acid the volatiles were removed in vacuo. The crude product was dry-loaded onto silica gel and purified via flash column chromatography (5–20

• combined organic layers were washed with brine and dried over magnesium sulfate. The solvents were removed and the remaining crude product was purified by flash column chromatography on silica gel (10–30% ethyl acetate in cyclohexane) to give 1.00 g of compound 4 (79%) as a white foam. TLC: 40% ethyl

Transition-metal-free intramolecular Friedel–Crafts reaction by alkene activation: A method for the synthesis of some novel xanthene derivatives

• Tülay Yıldız,
• İrem Baştaş and
• Hatice Başpınar Küçük

Beilstein J. Org. Chem. 2021, 17, 2203–2208, doi:10.3762/bjoc.17.142

• and were characterized by IR and GC–MS. All novel pruducts were characterized by IR, 1H NMR, 13C NMR, elemental analysis and GC–MS. The reactions were monitored by TLC using silica gel plates and the products were purified by flash column chromatography on silica gel (Merck; 230–400 mesh), eluting

Nomimicins B–D, new tetronate-class polyketides from a marine-derived actinomycete of the genus Actinomadura

• Zhiwei Zhang,
• Tao Zhou,
• Taehui Yang,
• Keisuke Fukaya,
• Enjuro Harunari,
• Shun Saito,
• Katsuhisa Yamada,
• Chiaki Imada,
• Daisuke Urabe and
• Yasuhiro Igarashi

Beilstein J. Org. Chem. 2021, 17, 2194–2202, doi:10.3762/bjoc.17.141

• medium, and the whole culture broth was extracted with 1-butanol. The extract was subjected to silica gel and ODS column chromatography, and the final purification was achieved by reversed-phase HPLC to yield two new spirotetronate polyketides, nomimicins B (1) and C (2), along with a known compound

• from the aqueous layer containing the mycelium. Evaporation of the solvent gave 3.8 g of extract from 2 L of A16 culture. The extract was subjected to silica gel column chromatography with a step gradient of CHCl3/MeOH (1:0, 20:1, 10:1, 4:1, 2:1, 1:1, and 0:1, v/v). Fraction 4 (4:1) was concentrated to

• silica gel column chromatography with a gradient of CHCl3/MeOH (1:0, 20:1, 10:1, 4:1, 2:1, 1:1, and 0:1, v/v). Fraction 7 (0:1) was concentrated to give 0.37 g of brown oil, which was then fractionated by ODS column chromatography with a gradient of MeCN + 0.1% HCO2H solution (2:8, 3:7, 4:6, 5:5, 6:4, 7

Facile and innovative catalytic protocol for intramolecular Friedel–Crafts cyclization of Morita–Baylis–Hillman adducts: Synergistic combination of chiral (salen)chromium(III)/BF₃·OEt₂ catalysis

• Karthikeyan Soundararajan,
• Helen Ratna Monica Jeyarajan,
• Raju Subimol Kamarajapurathu and
• Karthik Krishna Kumar Ayyanoth

Beilstein J. Org. Chem. 2021, 17, 2186–2193, doi:10.3762/bjoc.17.140

• filtration, the solvent was removed under reduced pressure and the crude product was purified on silica gel (using hexane/EtOAc) to afford the desired product 6a as a white solid (81%). Methyl 1H-indene-2-carboxylate (6a): Yield: 160 mg (81%); white solid; mp 85–87 °C; IR (cm−1): 3062, 2953, 2884, 1947, 1735