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

• relatively good yields. Notably, a low isolated yield was reported when starting from 2-(4-chlorobutyl)pyridine (n = 4) and this was attributed to the competing cyclization reaction affording cyclic pyridinium salts. The prominent 2-(diphenylphosphine)pyridine (4) has proved to be an interesting building

• treated with triflic anhydride to afford the corresponding triflate 55. Microwave-assisted reduction of compound 55 with pyridinium chloride afforded the α-chloropyridine derivative 56, which was further catalytically dehalogenated with palladium on carbon and formic acid to generate the pyridine scaffold

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

• effective molarity and the favorable orientation of the substrates inside the cavity [61]. Thus, a nanometer-sized macrocyclic receptor based on a photoactive porphyrin unit and anion-binding pyridinium and 1,2,3-triazolium units 15 was reported by Li and co-workers This receptor was synthesized via well

Bipolenins K–N: New sesquiterpenoids from the fungal plant pathogen Bipolaris sorokiniana

• Chin-Soon Phan,
• Hang Li,
• Simon Kessler,
• Peter S. Solomon,
• Andrew M. Piggott and
• Yit-Heng Chooi

Beilstein J. Org. Chem. 2019, 15, 2020–2028, doi:10.3762/bjoc.15.198

• previously reported sativene-type sesquiterpenoids 5 (isolated from B. eleusines and Cochliobolus sp., and from semi-synthetic analogue of prehelminthosporol with pyridinium chlorochromate or chromic acid) [1][4][18][26], 8 (isolated from B. eleusines) [3][6], and 10 (isolated from Bipolaris sp. and

Identification of optimal fluorescent probes for G-quadruplex nucleic acids through systematic exploration of mono- and distyryl dye libraries

• Xiao Xie,
• Michela Zuffo,
• Marie-Paule Teulade-Fichou and
• Anton Granzhan

Beilstein J. Org. Chem. 2019, 15, 1872–1889, doi:10.3762/bjoc.15.183

• pyridinium fragments have been described as bright, photostable stains for double-stranded DNA, although their interaction with G4 structures has not been assessed [68][69][70]. All dyes, except for distyryl derivative 6a and mono-styryl derivative 19a, were obtained through a piperidine-catalyzed

• : replacement of the 2,4-pyridinium unit in dye 1a with a 2,6-pyridinium (7a) or a 2,4-quinolizinium moiety (11a) leads to a blue shift of the absorption maximum, whereas all other heterocyclic units lead to significantly stronger (10a, 14a) and/or red-shifted (9a, 12a, 13a) absorption bands (Table 1 and Figure

•  4B). On the other hand, the nature of the substituent R in the 2,4-pyridinium unit has only a minor influence on the optical properties, and the absorption bands of the dyes 2a–6a are only slightly red-shifted (by 10–20 nm in MeOH) with respect to that of 1a. Fluorimetric response of dyes towards DNA

A metal-free approach for the synthesis of amides/esters with pyridinium salts of phenacyl bromides via oxidative C–C bond cleavage

• Kesari Lakshmi Manasa,
• Yellaiah Tangella,
• Namballa Hari Krishna and
• Mallika Alvala

Beilstein J. Org. Chem. 2019, 15, 1864–1871, doi:10.3762/bjoc.15.182

• 10.3762/bjoc.15.182 Abstract An efficient, simple, and metal-free synthetic approach for the N- and O-benzoylation of various amines/benzyl alcohols with pyridinium salts of phenacyl bromides is demonstrated to generate the corresponding amides and esters. This protocol facilitates the oxidative cleavage

• of a C–C bond followed by formation of a new C–N/C–O bond in the presence of K2CO3. Various pyridinium salts of phenacyl bromides can be readily transformed into a variety of amides and esters which is an alternative method for the conventional amidation and esterification in organic synthesis. High

• functional group tolerance, broad substrate scope and operational simplicity are the prominent advantages of the current protocol. Keywords: amidation; benzoylation; benzylamines; pyridinium salt of phenacyl bromides; Introduction Amidation and esterification are fundamental transformations in synthetic

Application of chiral 2-isoxazoline for the synthesis of syn-1,3-diol analogs

• Juanjuan Feng,
• Tianyu Li,
• Jiaxin Zhang and
• Peng Jiao

Beilstein J. Org. Chem. 2019, 15, 1840–1847, doi:10.3762/bjoc.15.179

• oxidation of the free hydroxy to the carboxy group via intermediary aldehyde was then examined. Swern or pyridinium chlorochromate (PCC) oxidation of 4 also gave a complicated mixture without the desired aldehyde detected. These failed reactions indicated that the 2-isoxazoline moiety could not survive

Complexation of 2,6-helic[6]arene and its derivatives with 1,1′-dimethyl-4,4′-bipyridinium salts and protonated 4,4'-bipyridinium salts: an acid–base controllable complexation

• Jing Li,
• Qiang Shi,
• Ying Han and
• Chuan-Feng Chen

Beilstein J. Org. Chem. 2019, 15, 1795–1804, doi:10.3762/bjoc.15.173

• complex H1·G1 was obtained by vapor diffusion of isopropyl ether into acetone. As shown in Figure 4, G1 was encapsulated in the cavity of H1 to form a 1:1 complex, in which G1 is distorted by the dihedral angle between the pyridinium rings of 33.19°. There exist multiple CH···π interactions between the

• protons of G1 and the aromatic rings of H1 with distances of 2.683 for A, 2.845 for B, 2.788 for C, 2.802 for D, and 2.868 Å for E, respectively. There also exist π–π stacking interactions between the pyridinium of G1 and the aromatic ring of H1 with the distance of 3.854 Å for F, a CH···O hydrogen bond

• Information File 1, Figure S92). The calculation results revealed the C–H···π interactions between the protons on the pyridinium ring of G1 and the benzene ring units of the host H4 and C–H···O hydrogen bonds between the protons of the methyl group and pyridinium rings of G1 and the oxygen atom of H4 with

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

• more. It was observed that most of the methods utilize 2-aminopyridines as one of the starting materials due to its binucleophilic nature; associated with exocyclic amino group and endocyclic pyridinium nitrogen [19]. Recently, A3 coupling of alkynes, aldehydes, and aminopyridines have been developed

• performed a Cu(OAc)2-Et3N-mediated coupling reaction of α-azido ketones 115 with pyridinium ylides 114 using oxygen as a green oxidant (Scheme 40). The oxo-functionality present in α-azido ketones increased its acidity thus making it a good organic synthon. Optimization of the reaction conditions revealed

• heterocycles. Pyridinium ylides used as 1,3-dipoles in this protocol were synthesized by the reaction of pyridines with α-bromo ketones (Scheme 41). The protocol was applicable to a series of EW and EDGs on phenacyl azides. However, the reaction was not successful with ethyl azidoacetate. On the other hand, EW

Superelectrophilic carbocations: preparation and reactions of a substrate with six ionizable groups

• Sean H. Kennedy,
• Makafui Gasonoo and
• Douglas A. Klumpp

Beilstein J. Org. Chem. 2019, 15, 1515–1520, doi:10.3762/bjoc.15.153

• (including methane) [6][7][8][9]. Numerous studies from our group and others have shown that relatively stable cationic centers – such as ammonium, phosphonium, and pyridinium groups – may also be part of superelectrophilic systems [10]. Recently, we described the chemistry of tri-, tetra-, and pentacationic

• high degree of delocalization into the neighboring phenyl group. Both the trication 3 and the tetracation 4 were directly observed from FSO3H–SbF5 solution using low temperature NMR. Experimental observations also revealed an exceptionally high acidity of the pyridinium N–H bonds. Here, we describe the

• position and deprotonation of the para-carbon to complete the arylation step. For the cyclization product 11, theoretical calculations indicate that cyclization requires deprotonation at the pyridinium ring [11]. Thus, either the tetracation 15 or the pentacation 16 is the likely precursor to the pyrido

Complexation of a guanidinium-modified calixarene with diverse dyes and investigation of the corresponding photophysical response

• Yu-Ying Wang,
• Yong Kong,
• Zhe Zheng,
• Wen-Chao Geng,
• Zi-Yi Zhao,
• Hongwei Sun and
• Dong-Sheng Guo

Beilstein J. Org. Chem. 2019, 15, 1394–1406, doi:10.3762/bjoc.15.139

• the dissolved pyridinium-N-phenoxidebetaine dye in a solvent, measured in kcal mol−1 [47]. The linear relationship between the maximum emission wavenumbers (ν̃, cm−1) and ET(30) for 2,6-TNS [ν̃ = −256ET(30) + 36431.5, R2 = 0.963] and 1.8-ANS [ν̃ = −159.8ET(30) + 29602.9, R2 = 0.986] were established

Host–guest interactions between p-sulfonatocalix[4]arene and p-sulfonatothiacalix[4]arene and group IA, IIA and f-block metal cations: a DFT/SMD study

• Valya K. Nikolova,
• Cristina V. Kirkova,
• Silvia E. Angelova and
• Todor M. Dudev

Beilstein J. Org. Chem. 2019, 15, 1321–1330, doi:10.3762/bjoc.15.131

• selectivities; they have demonstrated excellent complex ability towards inorganic cations, organic ammonium cations, pyridinium guests, neutral molecules (alcohols, ketones, nitriles), dye molecules, etc. [26]. p-Sulfonatocalix[n]arenes are complexing agents for structurally diverse biologically active

Electrophilic oligodeoxynucleotide synthesis using dM-Dmoc for amino protection

• Shahien Shahsavari,
• Dhananjani N. A. M. Eriyagama,
• Bhaskar Halami,
• Vagarshak Begoyan,
• Marina Tanasova,
• Jinsen Chen and
• Shiyue Fang

Beilstein J. Org. Chem. 2019, 15, 1116–1128, doi:10.3762/bjoc.15.108

• hydrophobic than the desired full-length sequence. Another consideration was that with acetic anhydride for capping, chances existed for replacing the dM-Dmoc groups with acetyl group during capping due to the presence of acids such as pyridinium acetate and large excess of acetic anhydride. Once the capping

Synthesis of 2H-furo[2,3-c]pyrazole ring systems through silver(I) ion-mediated ring-closure reaction

• Vaida Milišiūnaitė,
• Rūta Paulavičiūtė,
• Eglė Arbačiauskienė,
• Vytas Martynaitis,
• Wolfgang Holzer and
• Algirdas Šačkus

Beilstein J. Org. Chem. 2019, 15, 679–684, doi:10.3762/bjoc.15.62

• -inflammatory [5], and antidiabetic agents [6]. The numerous known methods for the preparation of these compounds are generally based on multicomponent reactions of an aromatic aldehyde, a β-keto ester, a hydrazine and malononitrile [7]. In a similar reaction using a pyridinium ylide instead of malononitrile

Syntheses and chemical properties of β-nicotinamide riboside and its analogues and derivatives

• Mikhail V. Makarov and
• Marie E. Migaud

Beilstein J. Org. Chem. 2019, 15, 401–430, doi:10.3762/bjoc.15.36

• chloride to yield the triacetylated chloride salt or with 2,3,5-tri-O-benzoyl-D-ribofuranosyl chloride to yield the tribenzoylated chloride salt. The halosugars were obtained from 1,2,3,5-tetra-O-acetyl-D-β-ribofuranose (2a) or 1-O-acetyl-2,3,5-tri-O-benzoyl-D-β-ribofuranose (2b) [21]. Both pyridinium

• conjugates of NR+. Modifications which include protection of 2′- and 3′-hydroxy goups and reduction of the pyridinium core are used when direct modifications at the 5′-position are not possible due to the cleavage of the glycosidic bond under the required conditions, or are troublesome due to the low

• results in the in situ generation of pyridinium hydroxide, resulting in further NR+ hydrolysis. This unfavorable reactivity of the C-1′ position was briefly addressed in the earlier sections of this review, as evidenced by the needs of anhydrous conditions and low temperatures in the deprotection steps to

Synthesis of nonracemic hydroxyglutamic acids

• Dorota G. Piotrowska,
• Iwona E. Głowacka,
• Andrzej E. Wróblewski and
• Liwia Lubowiecka

Beilstein J. Org. Chem. 2019, 15, 236–255, doi:10.3762/bjoc.15.22

• (2S,3R)-2 via Sharpless epoxidation. Reagents and conditions: a) TBHP, D-(−)-DIPT, Ti(OiPr)4, MS, CH2Cl2; b) t-BuMe2SiCl, imidazole, DMAP, DMF; c) NaIO4, RuO2, AcOEt/H2O. Synthesis of (2S,3S)-2 from the imide 51. Reagents and conditions: a) NaBH4, MeOH/CH2Cl2; b) Ac2O, pyridinium perchlorate; c) furan

Mn-mediated sequential three-component domino Knoevenagel/cyclization/Michael addition/oxidative cyclization reaction towards annulated imidazo[1,2-a]pyridines

• Olga A. Storozhenko,
• Alexey A. Festa,
• Delphine R. Bella Ndoutoume,
• Alexander V. Aksenov,
• Alexey V. Varlamov and
• Leonid G. Voskressensky

Beilstein J. Org. Chem. 2018, 14, 3078–3087, doi:10.3762/bjoc.14.287

• Chemistry, North Caucasus Federal University, Pushkin st. 1a, 355009 Stavropol, Russian Federation 10.3762/bjoc.14.287 Abstract The sequential three-component reaction between o-hydroxybenzaldehydes, N-(cyanomethyl)pyridinium salts and a nucleophile towards substituted chromenoimidazopyridines under

• , complicated by the need of an oxidant to fulfil the final aromatization. Following our interest in domino [42][43] and MCR chemistry [44][45] and taking an advantage of 2-iminochromene reactivity, herein we report a sequential three-component domino reaction of salicylaldehydes 2 and N-(cyanomethyl)pyridinium

• salts 1 with a broad scope of nucleophiles to produce diversely substituted valuable chromenoimidazopyridines under oxidative conditions (Scheme 1, reaction 2). Results and Discussion To prove the designed concept, the reaction between salicylaldehyde (2a), N-(cyanomethyl)pyridinium chloride (1) and

The influence of the cationic carbenes on the initiation kinetics of ruthenium-based metathesis catalysts; a DFT study

• Magdalena Jawiczuk,
• Angelika Janaszkiewicz and
• Bartosz Trzaskowski

Beilstein J. Org. Chem. 2018, 14, 2872–2880, doi:10.3762/bjoc.14.266

• recently and examples of their transition metal complexes are scarce. In 2013 Ganter described a cationic NHC with a fused pyridinium moiety and the formal +1 charge just one bond away from the imidazole core [27]. In 2017 César synthesized a cationic imidazolylidene NHC with an ammonium tag attached

Oxidative and reductive cyclization in stiff dithienylethenes

• Michael Kleinwächter,
• Ellen Teichmann,
• Lutz Grubert,
• Martin Herder and
• Stefan Hecht

Beilstein J. Org. Chem. 2018, 14, 2812–2821, doi:10.3762/bjoc.14.259

• reached within the redox window determined by the electrolyte. Thus, a strongly electron-deficient substituent such as pyridinium is necessary to shift the reduction potential to accessible values. However, not every electron-withdrawing group appears to be suited to induce cathodic cyclization [40][42

An overview on recent advances in the synthesis of sulfonated organic materials, sulfonated silica materials, and sulfonated carbon materials and their catalytic applications in chemical processes

• Hashem Sharghi,
• Pezhman Shiri and
• Mahdi Aberi

Beilstein J. Org. Chem. 2018, 14, 2745–2770, doi:10.3762/bjoc.14.253

• ) composite materials such as poly(1-vinyl-3-sulfo-1H-imidazolium chloride) grafted on MWCNT 100, poly(4-styrenesulfonic acid) grafted on MWCNT 101, and poly(4-vinyl-1-sulfo-pyridinium chloride) grafted on MWCNT 102 (CNT-PVSAIC, CNT-PSSA, and CNT-PVSAPC, respectively) was prepared (Scheme 18). Obtained

• adsorption showed some peaks at 1646, 1626, 1549 and 1476 cm−1. The peaks at 1646, 1626, and 1549 cm−1 could be due to the vibration of pyridinium (PyH+) species, corresponding to the existence of Brønsted acid sites on the s-MWCNTs 137. The peak at 1476 cm−1 was also labeled to the coordination of electron

Synthesis of 3-aminocoumarin-N-benzylpyridinium conjugates with nanomolar inhibitory activity against acetylcholinesterase

• Nisachon Khunnawutmanotham,
• Cherdchai Laongthipparos,
• Patchreenart Saparpakorn,
• Nitirat Chimnoi and
• Supanna Techasakul

Beilstein J. Org. Chem. 2018, 14, 2545–2552, doi:10.3762/bjoc.14.231

• well as with benzylpyridinium moieties [12][13][14] have been reported as dual-binding site AChE inhibitors. Recently we have reported the AChE inhibitory activity of the coumarin derivative, scopoletin conjugated with a pyridinium side chain (Figure 1) [15] and a docking study revealed that the

• conversion to N-acyl-3-aminocoumarins 4, 5, 9, and 10 did not lead to any improvement (% inhibitions of all compounds were less than 10% at 1 μM). In order to screen the AChE inhibitory activities of the pyridinium salts, compounds 4, 5, 9, and 10 were treated with benzyl bromide to provide the corresponding

• findings, the coumarin isonicotinamides 4 or 9 were selected as appropriate precursors for the preparation of the subsequent pyridinium salts. The presence of methoxy groups in the 6 and 7 positions of the coumarin ring remarkably enhanced the inhibitory activity against AChE as observed from the

Synergistic approach to polycycles through Suzuki–Miyaura cross coupling and metathesis as key steps

• Sambasivarao Kotha,
• Milind Meshram and
• Chandravathi Chakkapalli

Beilstein J. Org. Chem. 2018, 14, 2468–2481, doi:10.3762/bjoc.14.223

• cyclization with the aid of HCl followed by pyridinium dichromate (PDC) oxidation (Scheme 8). Schmidt and co-workers [39] described an efficient route involving RCM and SM coupling towards the synthesis of 8-aryl-substituted coumarin 64, a natural product isolated from the plant Galipea panamensis. To this

• . Then, the cyclized product was subjected to the oxidation sequence with pyridinium chlorochromate (PCC) to generate cylophane derivative 115 in 75% yield (Scheme 17). Similarly, treatment of dialdehyde 113 with a freshly prepared Grignard reagent derived from 4-bromobut-1-ene (116) afforded dialkenyl

Synthesis of eunicellane-type bicycles embedding a 1,3-cyclohexadiene moiety

• Alex Frichert,
• Peter G. Jones and
• Thomas Lindel

Beilstein J. Org. Chem. 2018, 14, 2461–2467, doi:10.3762/bjoc.14.222

• to the formation of pyridinium triflinate. It has also been reported that the triflinate anion can be generated from 2,6-lutidine/Tf2O [28] or Et3N/Tf2O [29]. Allenyl triflone 34 could be formed by attack of triflinate as S-nucleophile [30] at the chain carbon of propargyl cation 33. An alternative

A pyridinium/anilinium [2]catenane that operates as an acid–base driven optical switch

• Sarah J. Vella and
• Stephen J. Loeb

Beilstein J. Org. Chem. 2018, 14, 1908–1916, doi:10.3762/bjoc.14.165

• Sarah J. Vella Stephen J. Loeb Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario N9B 3P4, Canada 10.3762/bjoc.14.165 Abstract A two-station [2]catenane containing a large macrocycle with two different recognition sites, one bis(pyridinium)ethane and one

• bis(pyridinium)ethane site, while addition of acid forms a charged benzylanilinium site. The DB24C8 then shuttles between the two charged recognition sites with occupancy favoring the bis(pyridinium)ethane site by a ratio of 4:1. The unprotonated [2]catenane has a deep yellow/orange color when the

• DB24C8 ring resides solely at the bis(pyridinium)ethane site and changes to colorless when the crown ether is shuttling (i.e., circumrotating) back and forth between the two recognition sites thus optically signalling the onset of the shuttling dynamics. Keywords: catenane; mechanically interlocked

Synthesis of 9-arylalkynyl- and 9-aryl-substituted benzo[b]quinolizinium derivatives by Palladium-mediated cross-coupling reactions

• Siva Sankar Murthy Bandaru,
• Darinka Dzubiel,
• Heiko Ihmels,
• Mohebodin Karbasiyoun,
• Mohamed M. A. Mahmoud and
• Carola Schulzke

Beilstein J. Org. Chem. 2018, 14, 1871–1884, doi:10.3762/bjoc.14.161

• positively charged nitrogen atoms and π···π donor–acceptor attractions between the phenyl and pyridinium moieties. In our case, the situation is somehow more complex as the novel compounds bear aromatic substituents (via alkyne spacer) in the benzo[b]quinolizinium 9 position. These aromatic substituents now

• engage in π···π donor–acceptor attractions with the pyridinium moiety (outer most ring of the tricyclic moiety) and the two positively charged nitrogen atoms are per se much further apart due to the larger intramolecular separation between the intermolecularly interacting π-systems. In addition, the

• significant here and the preference for the anti-ht arrangement must be dominated by the π···π attractions. Centroid distances between the aromatic 9-substituent and the pyridinium moiety are 3.619 Å for 2a (C16 → C21; C5 → C9, N1) and 3.676 Å for 2b (C16 → C21; C1 → C5, N1), respectively (Figure S1

Mild and selective reduction of aldehydes utilising sodium dithionite under flow conditions

• Nicole C. Neyt and
• Darren L. Riley

Beilstein J. Org. Chem. 2018, 14, 1529–1536, doi:10.3762/bjoc.14.129

• ]. Sodium dithionite can act as a powerful reducing agent [16], is mild, easy to use, and it is compatible with protic solvents like water and isopropanol. It has previously been used to reduce a range of different organic functional groups including aldehydes and ketones [17][18], pyridinium ions to afford