HPW-Catalyzed environmentally benign approach to imidazo[1,2-a]pyridines

• Luan A. Martinho and
• Carlos Kleber Z. Andrade

Beilstein J. Org. Chem. 2024, 20, 628–637, doi:10.3762/bjoc.20.55

• synthesis of imidazo[1,2-a]pyridines is not as usual, given that Schiff bases from aliphatic aldehydes are found to be less stable and readily polymerize in comparison to stable Schiff bases of aromatic aldehydes. Nonetheless, our protocol for the HPW-catalyzed GBB multicomponent reaction proved to be very

pH-Responsive fluorescent supramolecular nanoparticles based on tetraphenylethylene-labelled chitosan and a six-fold carboxylated tribenzotriquinacene

• Nan Yang,
• Yi-Yan Zhu,
• Wei-Xiu Lin,
• Yi-Long Lu and
• Wen-Rong Xu

Beilstein J. Org. Chem. 2023, 19, 635–645, doi:10.3762/bjoc.19.45

• reaction to generate the corresponding multiple Schiff bases and then reduced with sodium borohydride (Scheme 1a). The structure of CS-TPE was characterized by 1H NMR spectra and solid-state CP/MAS 13C NMR spectra, and the results were found to agree with the proposed structure. For instance, the products

A new oxidatively stable ligand for the chiral functionalization of amino acids in Ni(II)–Schiff base complexes

• Alena V. Dmitrieva,
• Oleg A. Levitskiy,
• Yuri K. Grishin and
• Tatiana V. Magdesieva

Beilstein J. Org. Chem. 2023, 19, 566–574, doi:10.3762/bjoc.19.41

• derived from glycine Schiff bases containing a source of chirality is the most convenient and widely used template for modification of the glycine fragment under mild conditions. The template can be easily obtained via self-assembly of the starting components in the presence of metal ions (commonly Ni(II

Mechanochemical synthesis of unsymmetrical salens for the preparation of Co–salen complexes and their evaluation as catalysts for the synthesis of α-aryloxy alcohols via asymmetric phenolic kinetic resolution of terminal epoxides

• Shengli Zuo,
• Shuxiang Zheng,
• Jianjun Liu and
• Ang Zuo

Beilstein J. Org. Chem. 2022, 18, 1416–1423, doi:10.3762/bjoc.18.147

• and preparation of suitable salen compounds, sometimes are described as bis-imine Schiff bases. Imines were originally synthesized by Schiff from the condensation of carbonyls with amines [25]. Thereafter, syntheses of salens were extensively reported using timely technologies [26][27][28][29

Cyclodextrin-based Schiff base pro-fragrances: Synthesis and release studies

• Attila Palágyi,
• Jindřich Jindřich,
• Juraj Dian and
• Sophie Fourmentin

Beilstein J. Org. Chem. 2022, 18, 1346–1354, doi:10.3762/bjoc.18.140

• , we describe the synthesis of ten pro-fragrances – Schiff bases prepared from amino-β-cyclodextrin and common volatile aldehydes. Aldehydes constitute a prominent class of molecules broadly used as food product additives and are also key components of perfumes [24]. They were therefore chosen as an

• -β-CD (3j) upon time after successive extractions of the gaseous phase at different RH% values. Preparation of the Schiff bases from amino-β-CD 1 and aldehydes 2a–j. Yields: 3a, 96%; 3b, 83%; 3c, 91%; 3d, 86%; 3e, 82%; 3f, 96%; 3g, 89%; 3h, 97%; 3i, 80%; 3j, 83%. Henry law constants and formation

Facile and diastereoselective arylation of the privileged 1,4-dihydroisoquinolin-3(2H)-one scaffold

• Dmitry Dar’in,
• Grigory Kantin,
• Alexander Bunev and
• Mikhail Krasavin

Beilstein J. Org. Chem. 2022, 18, 1070–1078, doi:10.3762/bjoc.18.109

• by aromatic hydrocarbons (Figure 2) [13]. Herein, we describe the results obtained in the course of this investigation. Results and Discussion We began our investigation by synthesizing a sufficiently broad range of 3(2H)-isoquinolones 11 from phenylacetyl chlorides 12 and Schiff bases 13 using

Study on the interactions between melamine-cored Schiff bases with cucurbit[n]urils of different sizes and its application in detecting silver ions

• Jun-Xian Gou,
• Yang Luo,
• Xi-Nan Yang,
• Wei Zhang,
• Ji-Hong Lu,
• Zhu Tao and
• Xin Xiao

Beilstein J. Org. Chem. 2021, 17, 2950–2958, doi:10.3762/bjoc.17.204

• constructed by three different cucurbiturils and synthesized by guest melamine-cored Schiff bases (TBT) through outer-surface interaction and host–guest interactions. TBT forms a TMeQ[6]-TBT complex with TMeQ[6] through outer-surface interaction, while Q[7]-TBT and Q[8]-TBT form complexes with Q[7,8] through

• : cucurbiturils; melamine; Schiff base; silver ion; Introduction Schiff bases [1] are usually synthesized by the condensation of amines and active carbonyl compounds, endowing them both nitrogen and oxygen donor atoms [2][3][4][5]. Schiff bases are not only easy to coordinate with various transition metal ions

• to yield different metal-organic frameworks [6][7][8][9][10][11], but also can be used as analytical reagents for the detection of different organic and inorganic substances [12][13][14]. Among the various central molecules for the synthesis of Schiff bases, melamine (2,4,6-triamino-s-triazine) has

Photophysical, photostability, and ROS generation properties of new trifluoromethylated quinoline-phenol Schiff bases

• Inaiá O. Rocha,
• Yuri G. Kappenberg,
• Wilian C. Rosa,
• Clarissa P. Frizzo,
• Nilo Zanatta,
• Marcos A. P. Martins,
• Isadora Tisoco,
• Bernardo A. Iglesias and
• Helio G. Bonacorso

Beilstein J. Org. Chem. 2021, 17, 2799–2811, doi:10.3762/bjoc.17.191

• , Brazil Laboratório de Bioinorgânica e Materiais Porfirínicos, Departamento de Química, Universidade Federal de Santa Maria, Santa Maria, RS, 97105-900, Brazil 10.3762/bjoc.17.191 Abstract A new series of ten examples of Schiff bases, namely (E)-2-(((2-alkyl(aryl/heteroaryl)-4-(trifluoromethyl)quinolin-6

• , 4-NO2C6H4, and 2-furyl, and R1-substituents are 5-NEt2, 5-OCH3, 4-Br, and 4-NO2. Complementarily, the Schiff bases showed low to good quantum fluorescence yield values in CHCl3 (Φf = 0.12–0.80), DMSO (Φf = 0.20–0.75) and MeOH (Φf = 0.13–0.85). Higher values of Stokes shifts (SS) were observed in

• base; Introduction Schiff bases are an important class of organic compounds first reported by the German chemist Hugo Schiff in 1864 and are formed from the reversible condensation between a primary amine and an aldehyde or a ketone [1]. Also known as azomethines, aldimines, and more commonly as

Stereoselective synthesis and transformation of pinane-based 2-amino-1,3-diols

• Ákos Bajtel,
• Mounir Raji,
• Matti Haukka,
• Ferenc Fülöp and
• Zsolt Szakonyi

Beilstein J. Org. Chem. 2021, 17, 983–990, doi:10.3762/bjoc.17.80

• of the five components 15A–E were determined by 2D NMR spectroscopic techniques (NOESY and HMBC). Since this finding is quite unusual in the case of Schiff’ bases, we decided to study the ring/chain tautomeric mixture (15A–E) in the reaction of 13 with benzaldehyde by 1H NMR spectroscopy. When a time

Styryl-based new organic chromophores bearing free amino and azomethine groups: synthesis, photophysical, NLO, and thermal properties

• Anka Utama Putra,
• Deniz Çakmaz,
• Nurgül Seferoğlu,
• Alberto Barsella and
• Zeynel Seferoğlu

Beilstein J. Org. Chem. 2020, 16, 2282–2296, doi:10.3762/bjoc.16.189

• . The pH-sensitive properties of all prepared Schiff bases were examined against TBAOH in DMSO, via deprotonation of the OH group in the salicylidene moiety and their reverse protonation was also investigated using TFA. The Schiff bases exhibited a bathochromic shift upon the addition of TBAOH to their

• electron-accepting group coupled with various donors connected via a π-conjugation bridge [31][32][33]. Such dyes offer good NLO characteristics when compared to Disperse Red 1 as well as remarkable thermal stabilities with dissociation temperatures up to 300 °C [31][32]. Schiff bases containing an

• anticancer activity, to name a few. Moreover, Schiff bases bearing a salicylidene moiety are also used as chemosensors for sensing of specific ions. In addition, some derivatives also show NLO activity [25][34][35][36][37]. Herein, we report on the synthesis and full photophysical characterization of a

One-step route to tricyclic fused 1,2,3,4-tetrahydroisoquinoline systems via the Castagnoli–Cushman protocol

• Aleksandar Pashev,
• Nikola Burdzhiev and
• Elena Stanoeva

Beilstein J. Org. Chem. 2020, 16, 1456–1464, doi:10.3762/bjoc.16.121

• analogs 9 [12], and homophthalic anhydride (10) [13][14]) and imines 11, 12 offers a route to substituted lactam molecules 13 and 14 [13][14][15][16][17][18][19]. Among them, the reactions of homophthalic anhydride (10) with Schiff bases 11 or cyclic imines 12 have been examined in detail (Scheme 1) [13

• –8 was conducted in xylene under inert atmosphere at 120 °C (Scheme 4). Previous knowledge on the reaction between monocyclic anhydrides 5, 6 and 7 and Schiff bases indicated the necessity of elevated temperatures for conducting the reaction as the yields of the target products increased with the

Efficient synthesis of 4-substituted-ortho-phthalaldehyde analogues: toward the emergence of new building blocks

• Clémence Moitessier,
• Ahmad Rifai,
• Pierre-Edouard Danjou,
• Isabelle Mallard and
• Francine Cazier-Dennin

Beilstein J. Org. Chem. 2019, 15, 721–726, doi:10.3762/bjoc.15.67

• ], thioether macrocycles [11], macrocyclic Schiff bases [12] or even poly(phthalaldehyde) polymers [13]; taking into account that few studies were carried out with modified OPA on position 3 or 4. This could probably be due to the fact that the synthesis of 4-substituted OPA was, to the best of our knowledge

Targeting the Pseudomonas quinolone signal quorum sensing system for the discovery of novel anti-infective pathoblockers

• Christian Schütz and
• Martin Empting

Beilstein J. Org. Chem. 2018, 14, 2627–2645, doi:10.3762/bjoc.14.241

• facilitated the discovery of novel PqsD-targeting compounds through CuAAC-mediated conjugation of a fluorescent dye (Figure 9) [62]. Finally, Sangshetti et al. reported the discovery of linezolid-like Schiff bases, which showed promising anti-biofilm activity in the double-digit micromolar range [63]. Notably

Water-soluble SNS cationic palladium(II) complexes and their Suzuki–Miyaura cross-coupling reactions in aqueous medium

• Alphonse Fiebor,
• Richard Tia,
• Banothile C. E. Makhubela and
• Henok H. Kinfe

Beilstein J. Org. Chem. 2018, 14, 1859–1870, doi:10.3762/bjoc.14.160

• reactions [32][33]. As it was elegantly reviewed by Singh and co-workers [33], these organosulfur ligands can be classified into pincer type (symmetrical and unsymmetrical), thioethers, thiourea-based ligands, sulfur-substituted NHCs, thiosemicarbazones and sulfated Schiff bases. Of the pincer ligands

Synthesis of pyrimido[1,6-a]quinoxalines via intermolecular trapping of thermally generated acyl(quinoxalin-2-yl)ketenes by Schiff bases

• Svetlana O. Kasatkina,
• Ekaterina E. Stepanova,
• Maksim V. Dmitriev,
• Ivan G. Mokrushin and
• Andrey N. Maslivets

Beilstein J. Org. Chem. 2018, 14, 1734–1742, doi:10.3762/bjoc.14.147

• 3-acylpyrrolo[1,2-a]quinoxaline-1,2,4(5H)-triones react regioselectively with Schiff bases under solvent-free conditions to form pyrimido[1,6-a]quinoxaline derivatives in good yields. Keywords: acyl(quinoxalin-2-yl)ketenes; cycloaddition; pyrimido[1,6-a]quinoxalines; Schiff bases; thermolysis

• hetero-dienophiles published so far. In this article we report a synthetic protocol towards pyrimido[1,6-a]quinoxalines via the intermolecular trapping of acyl(quinoxalin-2-yl)ketenes by Schiff bases. Results and Discussion The most convenient method for the generation of acyl(quinoxalin-2-yl)ketenes is

• scope of the reaction applying the developed methodology with PQTs 1a–h and Schiff bases 2a–d. The results are shown in Figure 5. Unfortunately, our attempts to involve Schiff bases synthesized from aliphatic aldehydes and ketones did not give any satisfactory results because of various nucleophilic

Design, synthesis and structure of novel G-2 melamine-based dendrimers incorporating 4-(n-octyloxy)aniline as a peripheral unit

• Cristina Morar,
• Pedro Lameiras,
• Attila Bende,
• Gabriel Katona,
• Emese Gál and
• Mircea Darabantu

Beilstein J. Org. Chem. 2018, 14, 1704–1722, doi:10.3762/bjoc.14.145

• Background: 4-(n-Octyloxy)aniline is a known component in the elaboration of organic materials with mesogenic properties such as N-substituted Schiff bases, perylene bisimide assemblies with a number of 2-amino-4,6-bis[4-(n-octyloxy)phenylamino]-s-triazines, amphiphilic azobenzene-containing linear-dendritic

• concerning the utilisation of 4-(n-octyloxy)aniline, a “traditional” source for mesogenic N-substituted Schiff bases [26][27][28][29]. Following up our contributions in the field of dendritic melamines’ synthesis, structural analysis [30][31][32][33] and electrochemistry [34][35][36], we recently become

An overview of recent advances in duplex DNA recognition by small molecules

• Sayantan Bhaduri,
• Nihar Ranjan and
• Dev P. Arya

Beilstein J. Org. Chem. 2018, 14, 1051–1086, doi:10.3762/bjoc.14.93

• exceptionally stable duplexes (ΔTm = +44.8 °C) and high selectivity [92]. Six novel 4-aminoantipyrine derived Schiff bases and their metal complexes with Cu(II), Ni(II), Zn(II) ions (conjugates 26–31) were synthesized and characterized and binding of these complexes with ct-DNA were analyzed by electronic

Recent developments in the asymmetric Reformatsky-type reaction

• Hélène Pellissier

Beilstein J. Org. Chem. 2018, 14, 325–344, doi:10.3762/bjoc.14.21

• aldehydes as electrophiles [38]. Enantioselectivities of up to 84% ee were achieved by using a BINOL derivative as chiral ligand. Ever since, other types of chiral ligands including chiral Schiff bases [39], bisoxazolidines [40], 1,2-amino alcohols [41], indolinylmethanols [42], and diarylprolinols have

Synthesis of benzannelated sultams by intramolecular Pd-catalyzed arylation of tertiary sulfonamides

• Valentin A. Rassadin,
• Mirko Scholz,
• Anastasiia A. Klochkova,
• Armin de Meijere and
• Victor V. Sokolov

Beilstein J. Org. Chem. 2017, 13, 1932–1939, doi:10.3762/bjoc.13.187

• problem in the alkylation of the sulfonamide 3a, the sequence of steps was reversed. Thus, 2-iodo-N-(4-methoxybenzyl)anilines 7a–g were prepared by reduction of the Schiff bases obtained from 2-iodoanilines 1a–g and 4-methoxybenzaldehyde with sodium cyanoborohydride in a mixture of glacial acetic acid and

• -ortho-quinodimethane derivatives [44], which can rearrange into the corresponding Schiff bases by sigmatropic [1,5]-hydrogen shift [45]. In the case of 13, the extrusion of SO2 must be drastically accelerated due to its carbanionic nature, so that it can occur at 70 °C. The resulting anionic aza-ortho

New tricks of well-known aminoazoles in isocyanide-based multicomponent reactions and antibacterial activity of the compounds synthesized

• Maryna V. Murlykina,
• Maryna N. Kornet,
• Sergey M. Desenko,
• Svetlana V. Shishkina,
• Oleg V. Shishkin,
• Aleksander A. Brazhko,
• Vladimir I. Musatov,
• Erik V. Van der Eycken and
• Valentin A. Chebanov

Beilstein J. Org. Chem. 2017, 13, 1050–1063, doi:10.3762/bjoc.13.104

• 1f–h bearing strong electron-withdrawing groups under all the abovementioned conditions allowed isolating a mixture of imidazopyrazoles 4n–v with a large quantity of Schiff bases 5. Therefore, the conditions for the synthesis of compounds 4n–v were optimized employing 5-amino-N-(3-fluorophenyl)-1H

• the substitution pattern in the carbonyl component is related with the ability of the intermediate Schiff bases to be protonated as well as with their solubility. In case of the presence of electron-withdrawing substituents in the aldehyde the corresponding Schiff bases 5 are less soluble and less

• addition of HClO4 (10 mol %) upon stirring for 24 h (Table 5). On the other hand, condensation of the starting reagents 1d–g with 2a,b and 3b in EtOH/H2O (1:1) with TFA (10 mol %) resulted in the formation of the target products 6 in a mixture with a substantial amount of Schiff bases 5. Moreover, only

Development of chiral metal amides as highly reactive catalysts for asymmetric [3 + 2] cycloadditions

• Yasuhiro Yamashita,
• Susumu Yoshimoto,
• Mark J. Dutton and
• Shū Kobayashi

Beilstein J. Org. Chem. 2016, 12, 1447–1452, doi:10.3762/bjoc.12.140

• Schiff bases of glycine ester that proceed with low catalyst loadings (ca. 0.01 mol %). Catalytic asymmetric [3 + 2] cycloadditions of Schiff bases of α-amino esters to olefins are useful for synthesizing optically active pyrrolidine derivatives [10][11][12], and many highly stereoselective reactions

• revealed that the reaction proceeded with 0.01 mol % loading of chiral CuHMDS catalyst without significant loss of selectivity (Table 1, entry 11). We then examined the substrate scope of the [3 + 2] cycloaddition with respect to the Schiff base (Table 2). The Schiff bases prepared from tolualdehydes were

• loading, albeit with a slight decrease in the enantioselectivity (Table 2, entry 6). The use of Schiff bases bearing either electron-donating or electron-withdrawing substituents were also suitable, and high yields and enantioselectivities were obtained with both 0.1 and 0.01 mol % catalyst loading (Table

Synthesis, fluorescence properties and the promising cytotoxicity of pyrene–derived aminophosphonates

• Jarosław Lewkowski,
• Maria Rodriguez Moya,
• Anna Wrona-Piotrowicz,
• Janusz Zakrzewski,
• Renata Kontek and
• Gabriela Gajek

Beilstein J. Org. Chem. 2016, 12, 1229–1235, doi:10.3762/bjoc.12.117

• preliminary form [9], fluorescence emission of their azomethine precursors was reported for pyrene-1-carboxaldehyde thiosemicarbazone and Schiff bases as well as their metal complexes [16][17][18][19][20][21]. Such properties were described for, e.g., ruthenium(II) complexes of (5-chloropyridin-2-yl)-(pyren-1

• Synthesis of aminophosphonic acid derivatives 3, 4 and 5 Schiff bases 1a–h were prepared by refluxing pyrene-1-carboxaldehyde with an amine in methanol, hexane or dichloromethane for 24 hours and were used for further conversions as obtained. This harsh method to prepare imines had to be used, because the

• further reaction without purification. Aminophosphonates 3Aa–h, 3Ba–e and 3Ca–d, 3Cg have been synthesized via an aza-Pudovik reaction [22], i.e., the addition of the appropriate phosphite 2A–C to the azomethine bond of the Schiff bases 1a–h. Nevertheless, the important modifications had to be introduced

Olefin metathesis in air

• Lorenzo Piola,
• Fady Nahra and
• Steven P. Nolan

Beilstein J. Org. Chem. 2015, 11, 2038–2056, doi:10.3762/bjoc.11.221

• quantitative yields in the RCM, CM and ene–yne reactions. Furthermore, complexes 33 and 85 were able to perform the RCM reactions under the same conditions, with yields ranging from moderate to excellent (Figure 15). Schiff bases Schiff bases in metathesis are usually O,N-bidentate ligands and represent an

• atoms, O (hard) and N (soft), offer different features and therefore can stabilize, respectively, high and low oxidation states. Ruthenium carbene complexes bearing Schiff bases were synthesized originally by the Grubbs’ group and applied in RCM reactions [95], showing lower activity then the Grubbs 1st

Recent advances in the electrochemical construction of heterocycles

• Robert Francke

Beilstein J. Org. Chem. 2014, 10, 2858–2873, doi:10.3762/bjoc.10.303

• . described an indirect electrochemical method for the generation of 2-substituted benzoxazoles from Schiff bases (Scheme 19) [64]. Using 20 mol % NaI as redox mediator, the electrolysis is conducted under galvanostatic conditions in an undivided cell. A two-phase system composed of a sodium carbonate buffer

• ). Electrosynthesis of 39 as part of the total synthesis of alkaloids 40 and 41. Wacker-type cyclization of alkenyl phenols 42. Cathodic synthesis of indol derivatives. Fluoride mediated anodic cyclization of α-(phenylthio)acetamides. Synthesis of 2-substituted benzoxazoles from Schiff bases. Synthesis of euglobal

(2R,1'S,2'R)- and (2S,1'S,2'R)-3-[2-Mono(di,tri)fluoromethylcyclopropyl]alanines and their incorporation into hormaomycin analogues

• Armin de Meijere,
• Sergei I. Kozhushkov,
• Dmitrii S. Yufit,
• Christian Grosse,
• Marcel Kaiser and
• Vitaly A. Raev

Beilstein J. Org. Chem. 2014, 10, 2844–2857, doi:10.3762/bjoc.10.302

• of Schiff bases derived from glycine and (S)- or (R)-2-N-(N'-benzylprolyl)aminobenzophenone (BPB) [30][31], aminoacetophenone (BPA) [32] or aminobenzaldehyde (BPH) [33] can be used as chiral nucleophilic glycine equivalents in reactions with alkyl halides or carbonyl compounds. The most versatile one

• is the nickel(II) aminobenzophenone derivative. It is interesting that nickel(II) complexes of Schiff bases derived from 2-bromoglycine and (S)-BPB can be used as electrophilic glycine equivalents [34]. Alkylations of the nickel(II) complexes of Schiff bases derived from glycine and (S)- or (R)-BPB