Clickable azide-functionalized bromoarylaldehydes – synthesis and photophysical characterization

• Dominik Göbel,
• Marius Friedrich,
• Enno Lork and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2020, 16, 1683–1692, doi:10.3762/bjoc.16.139

• ISC processes through intermolecular halogen bonding to generate efficient RTP was initially investigated by Kim et al. [58]. They developed the minimalistic 2,5-dihexyloxy-4-bromobenzaldehyde (1) [59][60][61][62][63] which showed a weak fluorescence in solution, but exhibited a green phosphorescence

• with a quantum yield of ΦP = 2.9% in the crystalline state: this behavior was caused by intermolecular halogen bonds from the carbonyl-oxygen atom to an adjacent bromine atom (Figure 1a). Despite multifarious examples of RTP in the crystalline state, purely organic compounds showing RTP in solution are

Pauson–Khand reaction of fluorinated compounds

• Jorge Escorihuela,
• Daniel M. Sedgwick,
• Alberto Llobat,
• Mercedes Medio-Simón,
• Pablo Barrio and
• Santos Fustero

Beilstein J. Org. Chem. 2020, 16, 1662–1682, doi:10.3762/bjoc.16.138

• (Scheme 23) [59]. The authors rationalized the formation of 45 by considering that the inherent weakening of the C—X bond going down the halogen series may favor the generation of radical A with chloride and bromide derivatives, especially given the tertiary position of the halide and the stoichiometric

Models of necessity

• Timothy Clark and
• Martin G. Hicks

Beilstein J. Org. Chem. 2020, 16, 1649–1661, doi:10.3762/bjoc.16.137

• generally approached the subject. Specific potential functions are added to empirical force fields for hydrogen [87] or halogen [88] bonding. However, given that researchers have been busily defining additional non-covalent interactions such as tetrel [89], pnictogen [90] and chalcogen bonding [91], this

• approach leads to unnecessary complication of the model. As these interactions together with hydrogen and halogen bonding can all be treated within the single “σ-hole” framework [92], a single unified approach seems possible. However, such an approach would require a wave function or electron density

• interaction between halogens and nucleophiles as repulsive; whereas we now know that halogen-bonding attractions can be as strong as hydrogen bonds. There will be more such examples but it is important to identify the encompassing phenomenon, rather than defining a wealth of apparently unique interactions

One-pot synthesis of 1,3,5-triazine-2,4-dithione derivatives via three-component reactions

• Gui-Feng Kang and
• Gang Zhang

Beilstein J. Org. Chem. 2020, 16, 1447–1455, doi:10.3762/bjoc.16.120

• , and trifluoromethyl they smoothly took part in the three-component reaction and provided the desired products 6ja–na in moderate yields. It is noteworthy that benzaldehydes containing a halogen atom such as fluorine, chlorine, bromine, and iodine in the para and meta-positions were also compatible

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

• susceptibility of 2-chloro-N-phenethylacetamide (13), towards halogen exchange mediated by BTMS (Scheme 6). The reaction progress was monitored by 1H NMR spectroscopy monitoring the signals of the methylene groups C(O)CH2Cl in 13 vs C(O)CH2Br in the product 22 (see Figure S16 in Supporting Information File 1

• , CDCl3 (Table 3, entry 2, 42% conversion after 3 h) as well as lowering the temperature (Table 3, entry 3, rt, CDCl3, after 24 h 50% conversion into 22) slowed down the reaction. When TEA was added to the mixture, the halogen-exchange reaction slightly decreased (Table 3, entries 4 and 5). Remarkably

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

• phenyl as the residue R were selected as test cases for our proposed system. Over the last two decades, Knochel demonstrated the benefits of LiCl on the halogen–magnesium exchange rates [43] and on the organomagnesium solubility [44]. The most known example of this class is the isopropylmagnesium

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

• substitution of a halogen atom in α-halogenated oxime 80 by dicarbonyl compound 81 and oxidative cyclization (Scheme 30) [121]. The introduction of electron-donating substituents into the benzene ring of the oxime increases the yield of the reaction product (example 82d, 90%), and the introduction of the

• electron-withdrawing substituents decreases it (example 82e, 64%). Non-aromatic oximes of chloro- or bromoacetone are not suitable for this method; product 82f was observed in trace amounts. According to the proposed reaction pathway, the nucleophilic substitution of the halogen atom with the formation 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

• alkynes. They can also perform atom abstractions, in particular HATs and halogen abstractions [66]. The generation of such species generally occurs through the homolytic cleavage of a peripheral σ bond [67][68]. In the majority of the cases, a leaving group is reduced and fragments to the aryl radical

• , rendering the development of efficient methodologies for their formation of paramount importance. Building on the seminal work of Zard [124], NCRs have emerged as key reactive intermediates. The reductive cleavage of weak N–X (X = halogen, S, O) bonds using a stoichiometric initiator or high temperatures

Development of fluorinated benzils and bisbenzils as room-temperature phosphorescent molecules

• Shigeyuki Yamada,
• Takuya Higashida,
• Yizhou Wang,
• Masato Morita,
• Takuya Hosokai,
• Kaveendra Maduwantha,
• Kaveenga Rasika Koswattage and
• Tsutomu Konno

Beilstein J. Org. Chem. 2020, 16, 1154–1162, doi:10.3762/bjoc.16.102

• restriction of intramolecular motions [23]. Moreover, crystalline 2,5-dihexyloxy-4-bromobenzaldehyde displays green phosphorescence, which stems from rapid ISC due to the heavy atom effect via halogen bonding (C=O···Br) [24]. Moreover, benzophenone- or benzil-type molecules can achieve long-lived

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

• reactivity [25]. The triplet state energy of carbonyl compounds can also be transferred to halogen-containing compounds, leading to the homolytic dissociation of the carbon–halogen bond. This interaction has been studied for tert-butyl chloride, where the descendant radical is quite stabilized [26]. The

• household 23 W compact fluorescent light (CFL) bulb at ambient temperature [55]. A base, 2,6-lutidine, was used to neutralize traces of HX (X = halogen), which formed by the homolytic cleavage of the C–X bond of the haloalkanes 93 (Scheme 24). Among the aldehydes tested, benzaldehyde (8) and 4

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

• with chloroacetic anhydride. Having accessed compound 12, many other new compounds can also be prepared by replacing an amine with the halogen atom. With compounds 12 and 15 in hand, we then tried to synthesize target compound 17 (Scheme 4), which is a novel 18β-glycyrrhetinic acid derivative to

Reaction of indoles with aromatic fluoromethyl ketones: an efficient synthesis of trifluoromethyl(indolyl)phenylmethanols using K₂CO₃/n-Bu₄PBr in water

• Thanigaimalai Pillaiyar,
• Masoud Sedaghati and
• Gregor Schnakenburg

Beilstein J. Org. Chem. 2020, 16, 778–790, doi:10.3762/bjoc.16.71

• broad substrate scope, functional group tolerance, and simple purification technique is highly desired. In our continuous effort of synthesizing indole derivatives [29][30][31], herein, we report an efficient synthesis of multiple halogen-substituted (1H-indol-3-yl)methanol derivatives in the presence

• ketones were investigated, and the results are summarized in Table 2. Trifluoroacetophenones having a halogen substituent at the para-position of the phenyl ring such as p-F (2b), p-Cl (2c), and p-Br (2d) provided the corresponding trifluoro-1-(1H-indol-3-yl)ethan-1-ols 3b, 3c, and 3d in 97, 92 and 89

• scope of ketones was further extended with mixed halogen-substituted, pentafluoro or heptafluoro ketones such as 2-chloro-2,2-difluoro-1-phenylethan-1-one (2m), 2,2,3,3,3-pentafluoro-1-phenylpropan-1-one (2n) and 2,2,3,3,4,4,4-heptafluoro-1-phenylbutan-1-one (2o). All these reactions provided the

Cascade trifluoromethylthiolation and cyclization of N-[(3-aryl)propioloyl]indoles

• Ming-Xi Bi,
• Shuai Liu,
• Yangen Huang,
• Xiu-Hua Xu and
• Feng-Ling Qing

Beilstein J. Org. Chem. 2020, 16, 657–662, doi:10.3762/bjoc.16.62

• and agrochemical industries [3][4][5]. Traditional methods to access these compounds mainly include halogen–fluorine exchange of halomethyl sulfides and trifluoromethylation of sulfur-containing compounds [6][7][8]. Over the last decade, tremendous efforts have been triggered to develop methods for

Rhodium-catalyzed reductive carbonylation of aryl iodides to arylaldehydes with syngas

• Zhenghui Liu,
• Peng Wang,
• Zhenzhong Yan,
• Suqing Chen,
• Dongkun Yu,
• Xinhui Zhao and
• Tiancheng Mu

Beilstein J. Org. Chem. 2020, 16, 645–656, doi:10.3762/bjoc.16.61

• all with halogen anions), but also structural differences (e.g., crystal water, RhCl3 vs RhCl3·3H2O) of analogous Rh salts played an important role in the catalytic synthesis of benzaldehyde. Among all tested rhodium salts, RhCl3·3H2O afforded benzaldehyde in the highest yield and was chosen as the

• catalytic process giving aldehyde 31 with 77% yield. Also substrates comprising two halogen substituents performed well offering access to dihalogenated aldehydes 32–35 with yields between 76–81%. In addition, heterocyclic iodides were also amenable to the reductive carbonylation reaction and the

Asymmetric synthesis of CF₂-functionalized aziridines by combined strong Brønsted acid catalysis

• Xing-Fa Tan,
• Fa-Guang Zhang and
• Jun-An Ma

Beilstein J. Org. Chem. 2020, 16, 638–644, doi:10.3762/bjoc.16.60

• dr values, including alkyl or halogen-substituted phenyl and 2-naphthyl ketones (Scheme 2). Unfortunately, phenylglyoxal monohydrates bearing strong electron-withdrawing groups were not compatible with the current conditions. X-ray analysis of aziridine 4a confirmed the absolute configuration of the

Copper-catalyzed remote C–H arylation of polycyclic aromatic hydrocarbons (PAHs)

• Anping Luo,
• Min Zhang,
• Zhangyi Fu,
• Jingbo Lan,
• Di Wu and
• Jingsong You

Beilstein J. Org. Chem. 2020, 16, 530–536, doi:10.3762/bjoc.16.49

• electronic effects and steric hindrances. Arylating reagents with ortho-substituents led to slightly reduced yields (Scheme 2, 3f and 3i). Aryliodonium salts containing halogen substituents, especially bromo and iodo atoms, could afford the desired products in moderate to good yields (Scheme 2, 3j–n), making

Synthesis of 4-amino-5-fluoropyrimidines and 5-amino-4-fluoropyrazoles from a β-fluoroenolate salt

• Tobias Lucas,
• Jule-Philipp Dietz and
• Till Opatz

Beilstein J. Org. Chem. 2020, 16, 445–450, doi:10.3762/bjoc.16.41

• (5). First, a Finkelstein halogen exchange reaction and a dehydration reaction were combined to obtain fluoroacetonitrile (7) in 82% yield [36]. The latter then underwent a Claisen condensation with ethyl formate to obtain 8 in 77% yield with a purity of 90%. The product contained about 10% (1H NMR

Synthesis of six-membered silacycles by borane-catalyzed double sila-Friedel–Crafts reaction

• Yafang Dong,
• Masahiko Sakai,
• Kazuto Fuji,
• Kohei Sekine and
• Yoichiro Kuninobu

Beilstein J. Org. Chem. 2020, 16, 409–414, doi:10.3762/bjoc.16.39

• halogen substituents or sterical hindrance. A gram-scale synthesis of phenoxasilins and transformation of the amino groups in the phenoxasilin product were also achieved. We hope that the developed protocol will prove to be a useful and efficient method to synthesize six-membered silacyclic compounds

Six-fold C–H borylation of hexa-peri-hexabenzocoronene

• Mai Nagase,
• Kenta Kato,
• Akiko Yagi,
• Yasutomo Segawa and
• Kenichiro Itami

Beilstein J. Org. Chem. 2020, 16, 391–397, doi:10.3762/bjoc.16.37

• produces undesired cyclic compounds [14]. To design and synthesize a variety of HBC derivatives, methods for regioselective functionalization of HBC are in strong demand. As for functional groups on the HBC core, the introduction of halogen and boryl groups is an effective way to enable further

Architecture and synthesis of P,N-heterocyclic phosphine ligands

• Wisdom A. Munzeiwa,
• Bernard Omondi and
• Vincent O. Nyamori

Beilstein J. Org. Chem. 2020, 16, 362–383, doi:10.3762/bjoc.16.35

• Preparation of N-heterocyclic phosphines via P–C bond formation Nucleophilic substitution of halogens There are different methods that have been reported for the construction of the P–C bonds. Two approaches are possible using halogenated precursors. The first one is the organometal-halogen-phosphine route

• where the metalated organohalogen compound is reacted with the halogen phosphine. Alternatively, the metal phosphide can be reacted with an organohalogen compound leading to the desired product. The most commonly used trans-metalation reagents are Grignard [54] or organolithium reagents [55] and other

• lithium halogen elimination, halide migration, and ring-opening reactions [56][57]. Butylphosphines are also formed alongside the main product, and in most cases pure phosphine pyridines are obtained using column chromatography followed by extractions adding to the number of synthesis steps. This method

Formal preparation of regioregular and alternating thiophene–thiophene copolymers bearing different substituents

• Atsunori Mori,
• Keisuke Fujita,
• Chihiro Kubota,
• Toyoko Suzuki,
• Kentaro Okano,
• Takuya Matsumoto,
• Takashi Nishino and
• Masaki Horie

Beilstein J. Org. Chem. 2020, 16, 317–324, doi:10.3762/bjoc.16.31

• to afford the regioregular polythiophene in which 2,5-dihalo-3-substituted thiophene 1 is employed as a monomer precursor, converting to the corresponding organometallic monomer by a halogen−magnesium exchange reaction with a Grignard reagent. The employment of 1 leading to polythiophene has been

Synthesis of 3-alkenylindoles through regioselective C–H alkenylation of indoles by a ruthenium nanocatalyst

• Abhijit Paul,
• Debnath Chatterjee,
• Srirupa Banerjee and
• Somnath Yadav

Beilstein J. Org. Chem. 2020, 16, 140–148, doi:10.3762/bjoc.16.16

• different functional groups (Table 2). It was found that the reactions tolerated carboxylic acid, ketone, halogen (Cl, Br, I, and F), aldehyde, amide, primary amine, secondary amine, and phenolic functional groups to a reasonably acceptable extent. Recovery and recyclability of the Ru nanocatalyst The

Halogen-bonding-induced diverse aggregation of 4,5-diiodo-1,2,3-triazolium salts with different anions

• Xingyu Xu,
• Shiqing Huang,
• Zengyu Zhang,
• Lei Cao and
• Xiaoyu Yan

Beilstein J. Org. Chem. 2020, 16, 78–87, doi:10.3762/bjoc.16.10

• triazolium salts show diverse aggregation via halogen bonding between C–I bonds and anions. Triazolium with halide anions exists as a tetramer with saddle conformation. Triazolium tetrafluoroborate exists as a trimer with Chinese lantern shape conformation. Triazolium trifluoroacetate and acetate exist as

• dimers, respectively, while the former shows boat conformation and the latter forms rectangle conformation. Triazolium salts form a linear polymer with polyiodide. Keywords: aggregation; 4,5-diiodo-1,2,3-triazolium salts; halogen bond; non-covalent interaction; Introduction The halogen bond (XB) is a

• reported neutral 4-halo-1,2,3-triazolylidenes C [43], which had a carbene character with σ-donation at the carbon and a σ-hole at the halogen atom. XB is observed by single-crystal X-ray diffraction in their coinage metal complexes. Meanwhile, 4-bromo-1,2,3-triazolylidene can catalyze H/D exchange of

Functionalization of the imidazo[1,2-a]pyridine ring in α-phosphonoacrylates and α-phosphonopropionates via microwave-assisted Mizoroki–Heck reaction

• Damian Kusy,
• Agata Wojciechowska,
• Joanna Małolepsza and
• Katarzyna M. Błażewska

Beilstein J. Org. Chem. 2020, 16, 15–21, doi:10.3762/bjoc.16.3

• halogen substituent in the imidazo[1,2-a]pyridine ring on its reactivity in the Mizoroki–Heck reaction. We confined our studies to the analogs bearing substituents at positions 6, 7, and 8 of the six-membered ring of the imidazo[1,2-a]pyridine (1a–f, in Figure 1) [24]. We found that the reaction occurred

A combinatorial approach to improving the performance of azoarene photoswitches

• Joaquin Calbo,
• Aditya R. Thawani,
• Rosina S. L. Gibson,
• Andrew J. P. White and
• Matthew J. Fuchter

Beilstein J. Org. Chem. 2019, 15, 2753–2764, doi:10.3762/bjoc.15.266

• ). The ortho-halogen-substituted photoswitches also present an unexpected behavior, where very large differences in half-lives are predicted depending on the nature of the halogen atom (from 5 days in 4pzH-Cl2 to ca. 4000 days in 4pzH-F2, or from 2 minutes in 4pzMe-Cl2 to 26 days in 4pzMe-F2, Table 1