One-pot synthesis of isosorbide from cellulose or lignocellulosic biomass: a challenge?

• Isaline Bonnin,
• Raphaël Mereau,
• Thierry Tassaing and
• Karine De Oliveira Vigier

Beilstein J. Org. Chem. 2020, 16, 1713–1721, doi:10.3762/bjoc.16.143

• hydrolysis of cellulose and dehydration of sorbitol and sorbitans was studied and their efficiency decreased in the order of H2SO4 > triflic acid (HOTf) > trifluoroacetic acid (TFA) > Amberlyst-38 > HCl > HNO3. It was shown that when MCC was used as starting material, in the presence of Ru/C and H2SO4, 50

Rearrangement of o-(pivaloylaminomethyl)benzaldehydes: an experimental and computational study

• Csilla Hargitai,
• Györgyi Koványi-Lax,
• Tamás Nagy,
• Péter Ábrányi-Balogh,
• András Dancsó,
• Gábor Tóth,
• Judit Halász,
• Angéla Pandur,
• Gyula Simig and
• Balázs Volk

Beilstein J. Org. Chem. 2020, 16, 1636–1648, doi:10.3762/bjoc.16.136

• ; ring-chain tautomerism; Introduction In a preliminary publication [1] we disclosed that methylenedioxy-substituted o-(pivaloylaminomethyl)benzaldehyde (1a), when kept in dichloromethane (DCM) in the presence of a catalytic amount (0.13 equiv) of trifluoroacetic acid (TFA) for 72 h at room temperature

• ,S)-2-(2,2-Dimethylpropanoyl)-2,3-dihydro-1H-isoindol-1-yl](2-formylphenyl)methyl]-2,2-dimethylpropanamide (23a). Method A: This compound was prepared according to general procedure I using 1e (1.01 g, 4.61 mmol) and trifluoroacetic acid (35 µL, 53 mg, 0.46 mmol). The title compound (584 mg, 58%) was

Heterogeneous photocatalysis in flow chemical reactors

• Christopher G. Thomson,
• Ai-Lan Lee and
• Filipe Vilela

Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125

Synthesis of esters of diaminotruxillic bis-amino acids by Pd-mediated photocycloaddition of analogs of the Kaede protein chromophore

• Esteban P. Urriolabeitia,
• Pablo Sánchez,
• Alexandra Pop,
• Cristian Silvestru,
• Eduardo Laga,
• Ana I. Jiménez and
• Carlos Cativiela

Beilstein J. Org. Chem. 2020, 16, 1111–1123, doi:10.3762/bjoc.16.98

• . The resulting reddish solid was filtered off, washed with additional portions of distilled water until the smell of the trifluoroacetic acid disappeared (in general 3 × 10 mL was sufficient, but a larger amount could be necessary), dried in vacuo and characterized as the orthopalladated dimers 3a–f

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

• selective enzymatic hydrolysis of 64 using an acylase under mild conditions (pH 8.0, 40 °C, 4 d, with CoCl2 as co-factor) [51] (Scheme 14). 1.5. Direct radiofluorination of ʟ-phenylalanine The direct radiofluorination of ʟ-phenylalanine (66) with either [18F]F2 or [18F]AcOF in trifluoroacetic acid (TFA

Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches

• Rodrigo Costa e Silva,
• Luely Oliveira da Silva,
• Aloisio de Andrade Bartolomeu,
• Timothy John Brocksom and
• Kleber Thiago de Oliveira

Beilstein J. Org. Chem. 2020, 16, 917–955, doi:10.3762/bjoc.16.83

• contains both the substrate (dihydroartemisinic acid) and the photocatalyst (chlorophyll a). The combination of the extract with trifluoroacetic acid promptly furnishes artemisinin, under continuous-flow conditions (3 min) using red light (87% yield) or under blue light irradiation (5 min, 88% yield

Preparation of 2-phospholene oxides by the isomerization of 3-phospholene oxides

• Péter Bagi,
• Réka Herbay,
• Nikolett Péczka,
• Zoltán Mucsi,
• István Timári and
• György Keglevich

Beilstein J. Org. Chem. 2020, 16, 818–832, doi:10.3762/bjoc.16.75

• trifluoroacetic acid, a mixture containing the corresponding 2- and 3-phospholene oxides (4a and 1a) in a ratio of 11:89 was obtained. However, when phospholene oxide 1a was heated in neat methanesulfonic acid at 160 °C for 24 h, 4a and 1a in a ratio of 97:3 were obtained, but the yield of the mixture was 57% due

Efficient synthesis of piperazinyl amides of 18β-glycyrrhetinic acid

• Dong Cai,
• ZhiHua Zhang,
• Yufan Meng,
• KaiLi Zhu,
• LiYi Chen,
• ChangXiang Yu,
• ChangWei Yu,
• ZiYi Fu,
• DianShen Yang and
• YiXia Gong

Beilstein J. Org. Chem. 2020, 16, 798–808, doi:10.3762/bjoc.16.73

• based on the reaction of carboxylic acid with N-Boc-protected aliphatic diamine in the presence of activators and then deprotection of the tert‐butoxycarbonyl (Boc) group using trifluoroacetic acid (TFA) [20]. Compared with the mentioned methods, the latter method achieves the higher yield (up to 90

• factor is that the acidity of chloroacetic acid (pKa = 2.87) was stronger than that of acetic acid (pKa = 4.76). The procedure for the generation of byproduct 11 was similar to N-Boc-deprotection using trifluoroacetic acid. The effective synthesis of compound 10 was then explored (Table 3). In our

Fluorinated maleimide-substituted porphyrins and chlorins: synthesis and characterization

• Valentina A. Ol’shevskaya,
• Elena G. Kononova and
• Andrei V. Zaitsev

Beilstein J. Org. Chem. 2019, 15, 2704–2709, doi:10.3762/bjoc.15.263

• porphyrin 4a with maleic anhydride by analogy with a well-known standard procedure [39][40] provided the target maleimide-substituted porphyrin 5a in 42% yield, which contains four maleimide moieties in the structure. Treatment of porphyrin 5a with trifluoroacetic acid in CHCl3 resulted in the removal of

Synthesis of novel sulfide-based cyclic peptidomimetic analogues to solonamides

• José Brango-Vanegas,
• Luan A. Martinho,
• Lucinda J. Bessa,
• Andreanne G. Vasconcelos,
• Alexandra Plácido,
• Alex L. Pereira,
• José R. S. A. Leite and
• Angelo H. L. Machado

Beilstein J. Org. Chem. 2019, 15, 2544–2551, doi:10.3762/bjoc.15.247

• anhydride to yield 7. Despite the good results for the acetylation of peptides 6 with R = Me at room temperature, the reaction of the ones with R = n-hexyl needed to be conducted under heat conditions (50 °C). Acidic treatment of the acetates 7 with trifluoroacetic acid: triisopropylsilane decoupling

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

• way for late-stage modifications. In the same year, Yu’s group [122] reported a Pd(II)-catalyzed C–H trifluoromethylation of arenes with an electrophilic trifluoromethylation reagent using diverse heterocyclic directing groups. Notably, the presence of trifluoroacetic acid (TFA) is crucial for the Ar

1,2,3-Triazolium macrocycles in supramolecular chemistry

• Mastaneh Safarnejad Shad,
• Pulikkal Veettil Santhini and
• Wim Dehaen

Beilstein J. Org. Chem. 2019, 15, 2142–2155, doi:10.3762/bjoc.15.211

• , indicating that the DN24C8 unit moved toward the N-methyl-1,2,3-triazolium station and was now close to the NDI moiety. This pH-controlled switching process is reversible (e.g., after addition of trifluoroacetic acid the original state is regained). On the other hand, there were no considerable changes in

Design, synthesis and biological evaluation of immunostimulating mannosylated desmuramyl peptides

• Rosana Ribić,
• Ranko Stojković,
• Lidija Milković,
• Mariastefania Antica,
• Marko Cigler and
• Srđanka Tomić

Beilstein J. Org. Chem. 2019, 15, 1805–1814, doi:10.3762/bjoc.15.174

• racemic Boc-protected (adamant-1-yl)glycine [32] 2 using the carbodiimide EDC/HOBt method [21]. The obtained mixture of BocAdGly-ʟ-Ala-ᴅ-isoGlnOBn diastereoisomers was treated with trifluoroacetic acid in order to remove the Boc protecting group while the diastereoisomer 4 with ᴅ-ʟ-ᴅ amino acid sequence

• peptide moieties. The tert-butyl deprotection was accomplished using a selective reagent, trifluoroacetic acid (TFA). Side products derived from deacetylation of compound 10 have not been detected. The synthesis of benzyl-protected α-mannoside containing a (R)-hydroxyisobutyryl linker was previously

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

Synthesis and conformational preferences of short analogues of antifreeze glycopeptides (AFGP)

• Małgorzata Urbańczyk,
• Michał Jewgiński,
• Joanna Krzciuk-Gula,
• Jerzy Góra,
• Rafał Latajka and
• Norbert Sewald

Beilstein J. Org. Chem. 2019, 15, 1581–1591, doi:10.3762/bjoc.15.162

• Proteo 90 Å column (C12; 250 × 4.60 mm). Flow rate 1 mL min−1. Eluent A: H2O/CH3CN/TFA (trifluoroacetic acid – TFA) (95:4.9:0.1), eluent B: CH3CN/H2O/TFA (95:4.9:0.1). Preparative RP-HPLC was carried out with a Thermo Separation Products system consisting of a UV-1000 detector and a P-4000 pump equipped

Different reactivity of phosphorylallenes under the action of Brønsted or Lewis acids: a crucial role of involvement of the P=O group in intra- or intermolecular interactions at the formation of cationic intermediates

• Stanislav V. Lozovskiy,
• Alexander Yu. Ivanov and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2019, 15, 1491–1504, doi:10.3762/bjoc.15.151

• , indoles [30] or phenols [31]. Other arenes (benzene and its substituted derivatives) have not been involved in these reactions. Concerning electron-deficient allenes, bearing electron-withdrawing groups, there is only one example of a trifluoroacetic acid-promoted hydroarylation with indoles [30]. To the

Synthesis and biological evaluation of truncated derivatives of abyssomicin C as antibacterial agents

• Leticia Monjas,
• Peter Fodran,
• Johanna Kollback,
• Carlo Cassani,
• Thomas Olsson,
• Maja Genheden,
• D. G. Joakim Larsson and
• Carl-Johan Wallentin

Beilstein J. Org. Chem. 2019, 15, 1468–1474, doi:10.3762/bjoc.15.147

• bromide, see Supporting Information File 1) using 11 in the presence of trifluoroacetic acid afforded the corresponding homoallylic alcohol 14 and 15 in 84% and 92% yield, respectively. The next steps involved acylation of alcohol 14 and 15 using bromoacetyl bromide in refluxing toluene, which afforded

Genomics-inspired discovery of massiliachelin, an agrochelin epimer from Massilia sp. NR 4-1

• Jan Diettrich,
• Hirokazu Kage and
• Markus Nett

Beilstein J. Org. Chem. 2019, 15, 1298–1303, doi:10.3762/bjoc.15.128

• gradient of methanol in water supplemented with 0.1% (v/v) trifluoroacetic acid. The gradient conditions were as follows: 10% methanol for 5 min, from 10% to 100% over 35 min, 100% for 10 min, followed by 10% for 10 min. The flow rate was set to 1 mL/min. The elution of compounds was monitored with a diode

Understanding the unexpected effect of frequency on the kinetics of a covalent reaction under ball-milling conditions

• Ana M. Belenguer,
• Adam A. L. Michalchuk,
• Giulio I. Lampronti and
• Jeremy K. M. Sanders

Beilstein J. Org. Chem. 2019, 15, 1226–1235, doi:10.3762/bjoc.15.120

• , reported as mol % and documented in Supporting Information File 1. The solid product was dissolved in MeCN + 0.2% trifluoroacetic acid (TFA) at a concentration of 1 mg/mL and injected in the HPLC system. TFA was added to the sample for HPLC analysis to neutralize the base DBU and to quench the disulfide

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

• organocatalytic performance. Peptides 1 and 2 were subjected to Boc deprotection by treatment with 20% trifluoroacetic acid (TFA) in CHCl3 followed by TFA-catalyzed polymerization in the presence of furfuryl alcohol (10 equiv) according to a literature procedure described for PFA [17] (Scheme 2). The

• (50 mL), and brine (50 mL), and then dried over anhydrous Na2SO4 and concentrated under reduced pressure. General procedure B. The prolyl pseudo-peptides catalyst was dissolved in 3 mL of CH2Cl2 and treated with 1 mL of trifluoroacetic acid at 0 °C. The reaction mixture was allowed to reach room

• catalysts and their subsequent polymerization with furfuryl alcohol leading to the organocatalytic polymers 3 and 4. TFA = trifluoroacetic acid; PFA = polyfurfuryl alcohol. Screening of PFA-supported prolyl pseudo-peptide catalysts and the reaction conditions in a batch heterogeneous Michael addition. Main

Novel (2-amino-4-arylimidazolyl)propanoic acids and pyrrolo[1,2-c]imidazoles via the domino reactions of 2-amino-4-arylimidazoles with carbonyl and methylene active compounds

• Victoria V. Lipson,
• Tetiana L. Pavlovska,
• Nataliya V. Svetlichnaya,
• Anna A. Poryvai,
• Nikolay Yu. Gorobets,
• Erik V. Van der Eycken,
• Irina S. Konovalova,
• Svetlana V. Shiskina,
• Alexander V. Borisov,
• Vladimir I. Musatov and
• Alexander V. Mazepa

Beilstein J. Org. Chem. 2019, 15, 1032–1045, doi:10.3762/bjoc.15.101

• the intense signals that occur due to cleavage of the CF3COO− anion. Single crystal X-ray diffraction analysis of biphenyl compound 9i has finally proved the structures of the obtained products (Figure 3). Compound 9i exists as organic salt with trifluoroacetic acid in the crystal phase. The existence

• Specord M-82 spectrometer. The 1H NMR spectra were measured on a Varian Mercury VX-200 (200 MHz) and Bruker AM-400 spectrometer (400 MHz), 13C NMR spectra were measured on a Bruker AM-400 (100 MHz) and Bruker Avance DRX 500 (125 МHz) spectrometers in DMSO-d6, CDCl3 and trifluoroacetic acid (TFA) using TMS

A chemically contiguous hapten approach for a heroin–fentanyl vaccine

• Yoshihiro Natori,
• Candy S. Hwang,
• Lucy Lin,
• Lauren C. Smith,
• Bin Zhou and
• Kim D. Janda

Beilstein J. Org. Chem. 2019, 15, 1020–1031, doi:10.3762/bjoc.15.100

• , norheroin (1, Figure 3). Thus, norheroin (1) was synthesized according to literature procedure and purified by recrystallization [16]. Alkylation of 1 with tert-butyl bromoacetate and subsequent deprotection with trifluoroacetic acid yielded the N-glycine derivative of norheroin, 16. This critical

Synthesis of (macro)heterocycles by consecutive/repetitive isocyanide-based multicomponent reactions

• Angélica de Fátima S. Barreto and
• Carlos Kleber Z. Andrade

Beilstein J. Org. Chem. 2019, 15, 906–930, doi:10.3762/bjoc.15.88

• followed by formation of an acyclic depsipeptoid via Passerini reaction between acid 96, isocyanide 98 and aldehydes 97. Trifluoroacetic acid (TFA) allowed deprotection of the amine/acid groups. In the last step, a macrocyclization reaction via an intramolecular Ugi reaction provided the achievement of the

Solid-phase synthesis of biaryl bicyclic peptides containing a 3-aryltyrosine or a 4-arylphenylalanine moiety

• Iteng Ng-Choi,
• Àngel Oliveras,
• Lidia Feliu and
• Marta Planas

Beilstein J. Org. Chem. 2019, 15, 761–768, doi:10.3762/bjoc.15.72

• using 1-[(1-cyano-2-ethoxy-2-oxoethylidineaminooxy)dimethylaminomorpholino]uronium hexafluorophosphate (COMU), Oxyma and N,N’-diisopropylethylamine (DIPEA) in DMF overnight. After peptide elongation, an aliquot of the resulting resin 4 was treated with trifluoroacetic acid (TFA)/triisopropylsilane (TIS

The LANCA three-component reaction to highly substituted β-ketoenamides – versatile intermediates for the synthesis of functionalized pyridine, pyrimidine, oxazole and quinoxaline derivatives

• Tilman Lechel,
• Roopender Kumar,
• Mrinal K. Bera,
• Reinhold Zimmer and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2019, 15, 655–678, doi:10.3762/bjoc.15.61

• catalyst. However, the treatment of 3 with an excess of trifluoroacetic acid led to a mixture of β-ketoenamide 5 and pyridin-4-ol derivative 6. Thus, the carboxylic acid did not act as a catalyst in this reaction as expected, it was incorporated into the products! The unique mechanism leading to the β

• partially undergoes a subsequent intramolecular aldol-type condensation reaction to furnish the pyridin-4-ols. Therefore, trifluoroacetic acid or related fluorinated carboxylic acids [22] lead to mixtures of the two products as shown in Scheme 1. For other carboxylic acids the multistep reaction of the

• in the three-component reaction should be investigated by finding the proper substrates and conditions. The β-ketoenamides with N-formyl substituents should be valuable precursors for subsequent transformations. As expected, the reactions involving trifluoroacetic acid gave only low yields of the β