A dynamic combinatorial library for biomimetic recognition of dipeptides in water

• Florian Klepel and
• Bart Jan Ravoo

Beilstein J. Org. Chem. 2020, 16, 1588–1595, doi:10.3762/bjoc.16.131

• , selective binders for peptides are extremely desirable but also highly challenging to design. Early developments in artificial peptide recognition go back to the 1970’s when it was discovered that crown ethers can bind to ammonium functions, such as protonated amines in peptides [1]. Further such binding

• the parallel dimer of CHC (p(CHC)2), which binds two molecules of the neurotransmitter N-acetylneuraminic acid (NANA) in a cooperative fashion (K1 = 143, K2 = 5.1 × 103 M−1). Recently we rationalized that since our peptide building blocks consist of the same binding motifs as binding proteins (amines

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

• , first reported in 1834 by Liebig, which he named “melon” [119]. The material consists of two-dimensional sheets of hexatopic, hexagonal sp2-hybridised carbon and nitrogen atoms, linked by bridging tertiary amines (Figure 9) [120]. The material is crystalline as sheets are held together by strong π

• bipyridyl units have been designed to immobilise transition metal complexes through coordinate bonding for the oxidative coupling of amines [138]. [Ru(bpy)3]2+ units were synthesised with ethynyl groups para-substituted to the nitrogen heteroatom on four of the six pyridine rings. The ethynyl groups were

The McKenna reaction – avoiding side reactions in phosphonate deprotection

• Katarzyna Justyna,
• Joanna Małolepsza,
• Damian Kusy,
• Waldemar Maniukiewicz and
• Katarzyna M. Błażewska

Beilstein J. Org. Chem. 2020, 16, 1436–1446, doi:10.3762/bjoc.16.119

• step of the McKenna reaction. To this end, we used model compounds from our previous work, analyzed the possible side reactions, and proposed solutions in order to minimize or prevent the unwanted processes. We also showed that tertiary amines, that are commonly used as additives to prevent these side

• excess Et3N makes compound 12 more susceptible to N-alkylation. The reason for this observation might be the significantly higher basicity of Et3N (pKa 10.65) compared to 12, as approximated based on the pKas of representative amines resembling the structure of compound 12, Me3N (pKa 9.76) and

• allyldimethylamine (pKa 8.72), respectively [44]. This effect was reinforced by the higher nucleophilicity of the nitrogen atom in 12 compared with Et3N, as we deduced by comparison of model tertiary amines: Me3N (in MeCN: N 23.05, sN 0.45) and Et3N (in MeCN: N 17.10, sN 0.52) [45][46]. On the other hand, the lower

Recent synthesis of thietanes

• Jiaxi Xu

Beilstein J. Org. Chem. 2020, 16, 1357–1410, doi:10.3762/bjoc.16.116

• of amines. The latter then aminolyzed the carbamates 149 to generate ureas 151 and γ-halo-β-hydroxyalkanethiols 150. The intermediates 150 further underwent an intramolecular cyclization to produce the thietane-3-ols 145 in low to good yields [58] (Scheme 30). Paclitaxel (Taxol®) and docetaxel

Disposable cartridge concept for the on-demand synthesis of turbo Grignards, Knochel–Hauser amides, and magnesium alkoxides

• Mateo Berton,
• Kevin Sheehan,
• Andrea Adamo and
• D. Tyler McQuade

Beilstein J. Org. Chem. 2020, 16, 1343–1356, doi:10.3762/bjoc.16.115

• stratified packed-bed column of activated magnesium and lithium chloride. Scope of turbo Grignard reagents prepared under flow conditions.a Comparison of the batch [58] and flow conditions for the synthesis of iPrMgCl⋅LiCl. Reaction between amines and isopropylmagnesium chloride generated in situ. Knochel

Distinctive reactivity of N-benzylidene-[1,1'-biphenyl]-2-amines under photoredox conditions

• Shrikant D. Tambe,
• Kwan Hong Min,
• Naeem Iqbal and
• Eun Jin Cho

Beilstein J. Org. Chem. 2020, 16, 1335–1342, doi:10.3762/bjoc.16.114

• unprecedented reductive coupling of N-benzylidene-[1,1'-biphenyl]-2-amines with an aliphatic amine. The presence of a phenyl substituent in the aniline moiety of the substrate was critical for the reactivity. The reaction proceeded via radical–radical cross-coupling of α-amino radicals generated by proton

• -coupled single-electron transfer in the presence of an Ir photocatalyst. On the other hand, symmetrical 1,2-diamines were selectively produced from the same starting materials by the judicious choice of the reaction conditions, showcasing the distinct reactivity of N-benzylidene-[1,1'-biphenyl]-2-amines

• photocatalytic synthetic methods are mainly limited to aniline-based substrates and do not encompass aliphatic amines. We planned the synthesis of 1,2-diamine compounds having an aliphatic amine moiety by the intermolecular coupling of N-benzylidines with aliphatic amines that not only act as coupling partner

Photocatalytic trifluoromethoxylation of arenes and heteroarenes in continuous-flow

• Alexander V. Nyuchev,
• Ting Wan,
• Borja Cendón,
• Carlo Sambiagio,
• Job J. C. Struijs,
• Michelle Ho,
• Moisés Gulías,
• Ying Wang and
• Timothy Noël

Beilstein J. Org. Chem. 2020, 16, 1305–1312, doi:10.3762/bjoc.16.111

• soluble bases such as amines and tetrabutylammonium salts (Table 2, entries 1–5) proved unfortunately not successful, neither in batch nor flow, so we extended the investigation to inorganic bases. Among the bases tested, potassium hydrogenphosphates K2HPO4 and KH2PO4 led to increased yields, reaching up

Oxime radicals: generation, properties and application in organic synthesis

• Igor B. Krylov,
• Stanislav A. Paveliev,
• Alexander S. Budnikov and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2020, 16, 1234–1276, doi:10.3762/bjoc.16.107

• the relatively stable di-tert-butyliminoxyl radical was studied as a reagent in oxidative transformations of various substrates, such as unsaturated hydrocarbons, phenols, amines, and organometallic compounds. A breakthrough in the synthetic use of iminoxyl radicals has occurred in recent years when

• -iminooxycyclohexadienones 28a,b (Scheme 12). Phenol (29) and 1-naphthol (30) were transformed into 4,4-bisoximes 31 and 32, respectively (Scheme 12) [35][78]. Imines 37–40 were obtained with good yields by the reaction of di-tert-butyliminoxyl radicals with primary and secondary amines 33–36 for several hours at room

• using DTBP or aerial oxygen as an oxidant. Aliphatic, aromatic, and heteroaromatic amines 140, both primary and secondary, are applicable for this reaction. The reaction of TEMPO with β,γ- and γ,δ-unsaturated oximes 143 leads to substituted unsaturated isoxazolines 144 and cyclic nitrones 145

Activated carbon as catalyst support: precursors, preparation, modification and characterization

• Melanie Iwanow,
• Tobias Gärtner,
• Volker Sieber and
• Burkhard König

Beilstein J. Org. Chem. 2020, 16, 1188–1202, doi:10.3762/bjoc.16.104

• influence the yield of the materials. Thermally stable benzene moieties increase significantly the amount of carbon material produced, whereas mixtures based on amines or heterocycles decrease the yields [77]. The salt templating method developed of Antonietti and co-workers produces carbon materials with

• of activated carbons is possible at the precursor stage or as a modification step after the production of activated carbons and results mostly in a basic character of the prepared materials. Typical nitrogen agents are ammonia, urea or amines. Different types of nitrogen-containing functional groups

• amines, imines, amides, pyridine nitrogen and pyrrole nitrogen or as oxidized nitrogen species, e.g., pyridine-N-oxides [10]. Díaz-Terán et al. examined the surface of the samples (surface groups, chemical state of the elements, metal content and distribution) during the activation process of

Photocatalysis with organic dyes: facile access to reactive intermediates for synthesis

• Stephanie G. E. Amos,
• Marion Garreau,
• Luca Buzzetti and
• Jerome Waser

Beilstein J. Org. Chem. 2020, 16, 1163–1187, doi:10.3762/bjoc.16.103

• amines, with reduction potentials from 1.2 to 2.0 V vs SCE [138]. This has rendered the development of a general strategy for direct amidyl radical formations challenging. A successful approach has been the incorporation of a photolabile moiety on the nitrogen atom. Similar to the iminyl radical

• a reaction with oxygen. Finally, a remote functionalization of protected amines was also disclosed by Leonori and co-workers in their report on amidyl radical formations by SET oxidations of α-oxyamido acids using 4CzIPN (OD6, Scheme 28) [135]. Oxygen-centered radicals Oxygen-centered radicals (O

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

• the free amines gave amides 28a,b. Treatment of the latter with aqueous potassium hydroxide finally afforded (S)-2-amino-3-(2,3,4,5-tetrafluorophenyl)propionic acid (29a) and (S)-2-amino-3-(2,3,5,6-tetrafluorophenyl)propionic acid (29b) [42] (Scheme 6). Alternatively, phenylalanines 29a,b were also

• semicontinuous process was reported for the synthesis of racemic fluorinated phenylalanine·HCl starting from benzylamines 47a–c. Thus, a singlet oxygen-driven photooxidative cyanation of amines 47a–c using tetraphenylporphyrin (Tpp), followed by an acid-mediated hydrolysis of the intermediate fluorinated α-amino

Accelerating fragment-based library generation by coupling high-performance photoreactors with benchtop analysis

• Quentin Lefebvre,
• Christophe Salomé and
• Thomas C. Fessard

Beilstein J. Org. Chem. 2020, 16, 982–988, doi:10.3762/bjoc.16.87

• often exhibit different reactivity from unstrained substrates [8]. N-Arylation of spirocyclic amines would be a very efficient strategy for the modular synthesis of heterocyclic sp2–sp3 fragments, but their lack of stability to strongly basic conditions and heating might be an issue in palladium

• -catalyzed cross-coupling reactions [9]. Recently, milder cross-coupling methods using more abundant and affordable metals such as nickel, in combination with photochemistry or electrochemistry, significantly improved accessibility to N-arylated complex amines [10][11][12]. Results and Discussion As we

• temperatures and a mild base. Inspired by work at Merck on chemical informers, we decided to exploit our library of spirocyclic amines and strained scaffolds to generate a focused list of potential products [13]. We wanted to perform parallel reactions on small scale to gain further knowledge on the reactivity

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

• (1.87 nm), acts as a size-selective photocatalyst. Furthermore, the photocatalytic activity of 2D-COF is lower due to the π–π interaction between framework layers. Nitrogen oxidation: Amines are well-known as very efficient physical and chemical quenchers for singlet oxygen [67][100][101]. A myriad of

• ion, then giving an imine after deprotonation (Scheme 50). Adopting this strategy, Che and co-workers obtained several imines in 90–99% yield from secondary amines [102] (Scheme 51). The authors observed that the oxidation is regioselective, occurring at the less substituted position of nonsymmetric

• dibenzylamines, and they have demonstrated scalability of the protocol (products in up to 3.8 g scale). Similarly, using Pd-TPFPP the oxidation of amines to imines was achieved in 88–99% yields with low loading (0.005 mol %, 13000 TON h−1) after 1.5 h of irradiation with visible light (Scheme 52) [97]. The

Synthesis of new asparagine-based glycopeptides for future scanning tunneling microscopy investigations

• Laura Sršan and
• Thomas Ziegler

Beilstein J. Org. Chem. 2020, 16, 888–894, doi:10.3762/bjoc.16.80

• amines were used for the next step without further purification. In all cases, only the β-anomeric glycosylpeptides were obtained from the anomeric mixtures of amines (see below). The glycosylated aspartic acids 3 (except for 3d and 3f) were prepared previously with the help of different types of

Aldehydes as powerful initiators for photochemical transformations

• Maria A. Theodoropoulou,
• Nikolaos F. Nikitas and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2020, 16, 833–857, doi:10.3762/bjoc.16.76

• ]. Benzaldehyde (8) was tested as an alternative to tertiary amines, which are commonly employed in radical-mediated reactions due to their ability to bind to atmospheric oxygen, which inhibits such reactions. The quinoxalines 32 were used as the prime photoinitiators, and the reaction was placed in a

Photocatalytic deaminative benzylation and alkylation of tetrahydroisoquinolines with N-alkylpyrydinium salts

• David Schönbauer,
• Carlo Sambiagio,
• Timothy Noël and
• Michael Schnürch

Beilstein J. Org. Chem. 2020, 16, 809–817, doi:10.3762/bjoc.16.74

• methods for C–C bond formation at the α position of these amines have been studied under photoredox catalysis (Scheme 1) [23][24][25][26]. Among the functionalized THIQs, 1-benzyl-substituted analogues were shown to be able to modulate Ca/K channels, and the synthesis of these compounds is therefore of

• these compounds are either free amines or N-alkylated [48][49]. Hence, we tested the oxidative cleavage of the PMP group of compound 24 (Scheme 4), with ceric ammonium nitrate (CAN) [50][51]. After column chromatography, 50% of the desired free amine were isolated, which made this method a viable route

• from amino acids gave a complex reaction mixture, and the desired products could not be isolated. Additionally, alkyl salts derived from primary amines were unreactive. For the more stable allyl radicals, our initially optimized conditions with [Ru(bpy)3]Cl2 in DMA/ACN were again applicable and the

Efficient synthesis of dipeptide analogues of α-fluorinated β-aminophosphonates

• Marcin Kaźmierczak and
• Henryk Koroniak

Beilstein J. Org. Chem. 2020, 16, 756–762, doi:10.3762/bjoc.16.69

• , as well as J-couplings) a relative configuration of N,N-dibenzyl-protected α-fluoro-β-aminophosphonates 11 was established as (1R,2S), but we failed to crystallize these compounds [31]. That is why the removal of the benzyl protecting group from fluorides 11 and the transfer of the free amines 13

• (TFE) as a solvent [34][35]. The free amines 13 were converted into stable oxalate salts 14 with quantitative yields. The precipitation reactions proceeded in the presence of 1 equiv of oxalic acid in diethyl ether (Scheme 3) [36]. Unlike amines 13, salts 14 are very stable and can be stored for months

•  3). The correct absolute configuration was determined on the basis of Flack and Parson’s parameters, as well as of slightly better R factors for the correct model. Moreover, amines 13 were used as substrates in the formation of peptide bonds with N-Boc-phenylalanine (Boc-Phe-OH, Scheme 4). For this

Recent advances in Cu-catalyzed C(sp³)–Si and C(sp³)–B bond formation

• Balaram S. Takale,
• Ruchita R. Thakore,
• Elham Etemadi-Davan and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2020, 16, 691–737, doi:10.3762/bjoc.16.67

• -divergent borylative coupling of styrenes 395 with N-phosphinoyl and N-thiophosphinoyl imines 394 to afford α,β-disubstituted γ-borylated nonracemic amines 396–399. A combination of CuMes with either (R,R)-Ph-BPE or (R)-(Sp)-Josiphos afforded the targeted products in high ees (Scheme 63). The asymmetric

Microwave-assisted efficient and facile synthesis of tetramic acid derivatives via a one-pot post-Ugi cascade reaction

• Yong Li,
• Zheng Huang,
• Jia Xu,
• Yong Ding,
• Dian-Yong Tang,
• Jie Lei,
• Hong-yu Li,
• Zhong-Zhu Chen and
• Zhi-Gang Xu

Beilstein J. Org. Chem. 2020, 16, 663–669, doi:10.3762/bjoc.16.63

• removing the solvent under a gentle stream of nitrogen. Different amines, acids, and isonitriles were subjected to the one-pot protocol to give the corresponding tetramic acid derivatives 7 from the ketone intermediates 6 in good yields over two steps (51–75%) after the purification of the products by

• column chromatography (Scheme 2). It was found that the reaction showed a good functional group tolerance; no matter if R2 was electron-withdrawing or electron-donating, the target compounds could all be obtained in good yields. And aromatic or aliphatic amines (as R1) all gave the targeted products with

Preparation and in situ use of unstable N-alkyl α-diazo-γ-butyrolactams in Rh^II-catalyzed X–H insertion reactions

• Maria Eremeyeva,
• Daniil Zhukovsky,
• Dmitry Dar’in and
• Mikhail Krasavin

Beilstein J. Org. Chem. 2020, 16, 607–610, doi:10.3762/bjoc.16.55

• found to be unstable and to undergo unproductive dimerization to bishydrazones, were successfully converted immediately to various X–H insertion products with alcohols, aromatic amines and thiols via an in situ RhII-catalyzed reaction. With aliphatic amines or unreactive, sterically hindered anilines

• formation, in various RhII-catalyzed X–H insertion reactions, particularly the recently described rhodium carbene insertion into O–H [1], N–H [2] and S–H [3] bonds of alcohols, aromatic amines, and thiols, respectively. Herein, we report the results of these studies. Results and Discussion Three N-alkyl-α

• experimentation, the reactions with alcohols and thiols were found to be efficiently catalyzed by 1 mol % of Rh2(OAc)4 and completed within 30 min. For aromatic amines, this catalyst proved inefficient and was replaced by 0.5 mol % of Rh2(esp)2. The attempted change of the catalyst to Rh2(esp)2 in the reactions

Exploring the scope of DBU-promoted amidations of 7-methoxycarbonylpterin

• Anna R. Bockman and
• Jeffrey M. Pruet

Beilstein J. Org. Chem. 2020, 16, 509–514, doi:10.3762/bjoc.16.46

• explored this reaction to assess its scope and identify structural features in the amines which significantly affect success, monitored the reaction kinetics using a pseudo-first order kinetics model, and further adapted the reaction conditions to allow for product formation in as little as 5 min, with

• the order of several hours. Viewing this reaction as an essential tool for pteridine chemists seeking to rapidly generate diverse pterin structures, we sought to explore the scope of amines which can be easily appended to the pterin core. Trends in reactivity were further probed by monitoring the

• amines screened to react. This preliminary screen of amines gave acceptable yields for a range of substituted amines, with primary amines often giving the best results, as expected. To streamline the amine screening and allow for better comparisons of reactivity, a variety of times and temperatures were

KOt-Bu-promoted selective ring-opening N-alkylation of 2-oxazolines to access 2-aminoethyl acetates and N-substituted thiazolidinones

• Qiao Lin,
• Shiling Zhang and
• Bin Li

Beilstein J. Org. Chem. 2020, 16, 492–501, doi:10.3762/bjoc.16.44

• reactions using potassium tert-butoxide as promoter. Wu developed an efficient protocol for the KOt-Bu-promoted synthesis of 1-aminoisoquinolines from 2-methylbenzonitriles and benzonitriles [23], and the carbonylative cyclization of propargylic amines with selenium under CO gas-free conditions [24]. Based

• limitations of this KOt-Bu-promoted ring-opening N-alkylation from alkyl bromides with 2-methyl-2-oxazolines were explored using the optimized conditions. As shown in Scheme 2, various benzyl bromides bearing -Me, -t-Bu, -F, and -Cl groups were applied in the synthesis and afforded the tertiary amines 3a–g in

Aerobic synthesis of N-sulfonylamidines mediated by N-heterocyclic carbene copper(I) catalysts

• Faïma Lazreg,
• Marie Vasseur,
• Alexandra M. Z. Slawin and
• Catherine S. J. Cazin

Beilstein J. Org. Chem. 2020, 16, 482–491, doi:10.3762/bjoc.16.43

• conversion. Interestingly, in the case of 11r, the desired product was obtained in 67% isolated yield. The effect of the amines was also investigated. Amongst the amines evaluated, dicyclohexylamine (for 12a) and isopropylamine (for 12b) lead to good isolated yields (64% and 72%, Scheme 5). In contrast, with

Photophysics and photochemistry of NIR absorbers derived from cyanines: key to new technologies based on chemistry 4.0

• Bernd Strehmel,
• Christian Schmitz,
• Ceren Kütahya,
• Yulian Pang,
• Anke Drewitz and
• Heinz Mustroph

Beilstein J. Org. Chem. 2020, 16, 415–444, doi:10.3762/bjoc.16.40

• . The nitrogens in the cyanine chain still exhibit low nucleophilicity since electron density distributes over the entire methine chain. Thus, protonation of the nitrogen in the cyanine moiety occurs with less efficiency compared to amines [117]. This strategy helped to enable cationic

• shown to realize photoinitiated controlled/living radical polymerization of various monomers in metal free conditions. In the visible region, several dyes (fluorescein, eosin Y, erythrosin B) worked well to mediate ATRP in the presence of amines [72]. The reversibility of the electron transfer steps

Visible-light-induced addition of carboxymethanide to styrene from monochloroacetic acid

• Kaj M. van Vliet,
• Nicole S. van Leeuwen,
• Albert M. Brouwer and
• Bas de Bruin

Beilstein J. Org. Chem. 2020, 16, 398–408, doi:10.3762/bjoc.16.38

• . Single-electron oxidation can produce carbon-centered radicals from substrates such as amines [17], alkenes [18], and carboxylates [19], or by hydrogen-atom transfer to an oxidatively formed thiolate radical [20]. Single-electron reduction produces carbon-centered radicals from, for example, aryl