Tying a knot between crown ethers and porphyrins

• Maksym Matviyishyn and
• Bartosz Szyszko

Beilstein J. Org. Chem. 2023, 19, 1630–1650, doi:10.3762/bjoc.19.120

• macrocycles. The formation of (29b)2-Hg was reversible – its reaction with [2.2.2]cryptand resulted in the removal of mercury(II) and the contraction to 29b. Recently, Sessler and co-workers synthesised a new macrocycle 36 exploiting a pyridine-bridged dipyrroledialdehyde 35 (Scheme 10) [131]. The compound

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

• acid 144, Cbz removal of the macrocycle 145 formed led to another diamine intermediate that was involved in a second double Ugi reaction with paraformaldehyde, tert-butyl isocyanide and diacid 146, to yield cryptand 147 in 31% overall yield from 130. Other macroheterocycles were synthesized in this

First synthesis of cryptands with sucrose scaffold

• Patrycja Sokołowska,
• Michał Kowalski and
• Sławomir Jarosz

Beilstein J. Org. Chem. 2019, 15, 210–217, doi:10.3762/bjoc.15.20

• -chloroethyl) ether; this process provided an intermediate 9 in good yield. Replacement of both terminal chlorine atoms by iodine afforded compound 10, which was reacted with commercially available diaza-crown ether 8 to afford the first sucrose cryptand 11 in excellent yield (33%, Scheme 1). The structure of

• this first sucrose cryptand, suggested by HRMS analysis [m/z = 1285.6803 which corresponds to (C74H97N2O17 + H+)], was confirmed by the NMR data. In the 13C NMR spectrum of the final compound, six characteristic signals at δ ≈ 50–60 ppm were observed. They can be assigned to the methylene groups

• connected to the nitrogen atoms (-CH2N units), and thus this observation confirms the presence of the crown-unit 8 in the structure. Although the first approach to sucrose cryptands was very successful, the strategy based on sucrose diol 3 has several limitations. First of all, the cavity in cryptand 11 is

A three-armed cryptand with triazine and pyridine units: synthesis, structure and complexation with polycyclic aromatic compounds

• Claudia Lar,
• Adrian Woiczechowski-Pop,
• Attila Bende,
• Ioana Georgeta Grosu,
• Natalia Miklášová,
• Elena Bogdan,
• Niculina Daniela Hădade,
• Anamaria Terec and
• Ion Grosu

Beilstein J. Org. Chem. 2018, 14, 1370–1377, doi:10.3762/bjoc.14.115

• , Slovakia 10.3762/bjoc.14.115 Abstract The aromatic nucleophilic substitution reaction based synthesis of a three-armed cryptand displaying 2,4,6-triphenyl-1,3,5-triazine units as caps and pyridine rings in the bridges, along with NMR, MS and molecular modelling-based structural analysis of this compound

• are reported. Appropriate NMR and molecular modelling investigations proved the formation of 1:1 host–guest assemblies between the investigated cryptand and some polynuclear aromatic hydrocarbons or their derivatives. Keywords: aromatic guests; aromatic nucleophilic substitution; cryptand; NMR

• ]. The synthesis of cryptands with C3 symmetry by peculiar reactions (acetylenic coupling [16][17][18], CuAAC [19][20][21][22], double or triple bond metathesis [23][24][25], aromatic nucleophilic substitutions [26][27][28][29][30][31][32][33], or via the amplification of a cryptand belonging to DCC

Bright molecules for sensing, computing and imaging: a tale of two once-troubled cities

• A. Prasanna de Silva

Beilstein J. Org. Chem. 2015, 11, 2774–2784, doi:10.3762/bjoc.11.298

• amine [3][24][30], an amino acid [18][31], a crown ether [32] or a cryptand [33] and the spacer could be an oligomethylene chain [34] or nothing at all [35][36]. Since such diverse systems allow the addressing of various problems and since the design is usually straightforward, the PET sensor/switch

Selected synthetic strategies to cyclophanes

• Sambasivarao Kotha,
• Mukesh E. Shirbhate and
• Gopalkrushna T. Waghule

Beilstein J. Org. Chem. 2015, 11, 1274–1331, doi:10.3762/bjoc.11.142

• and nanomaterials is a challenging task. Huang and co-workers [165] have reported a taco complex template method to synthesize a cryptand/paraquat [2]rotaxane and [2]catenane (e.g., 207) by using RCM as a key step. Structural features and interesting bioactivity of the hirsutellones have grabbed the

Host–guest complexes of mixed glycol-bipyridine cryptands: prediction of ion selectivity by quantum chemical calculations, part V

• Svetlana Begel,
• Ralph Puchta and
• Rudi van Eldik

Beilstein J. Org. Chem. 2013, 9, 1252–1268, doi:10.3762/bjoc.9.142

• Lehn 40 years ago [37] is still very popular and widely used today, especially due to its ability to bind ions selectively, primarily alkali and alkaline earth metal cations [38][39][40][41][42][43][44][45][46][47][48][49]. In contrast, derivatives of this cryptand containing, for example, nitrogen

• and energies of model reactions, as was shown in previous contributions from our group [1][2][3][4]. A comparison of the bond distances between the donor atoms and the metal cation complexed endohedrally by the cryptand or by the solvent molecules, e.g., pyridine or water, can be drawn. This method

• too large for the studied cryptand. As depicted in Figure 6, the interaction of both Nsp2 atoms of the bipyridine side of the [2.2.bpy] with all presented cations is essential. The bridgehead Nsp3 atoms also play an important role for many of the studied ions, such as Ga3+, Tl3+, In3+, Ca2+, Sr2+, K

Fifty years of oxacalix[3]arenes: A review

• Kevin Cottet,
• Paula M. Marcos and
• Peter J. Cragg

Beilstein J. Org. Chem. 2012, 8, 201–226, doi:10.3762/bjoc.8.22

• not interact with the uranyl moiety (Figure 18). Replacing the alkylammonium cations with protonated [2.2.2]cryptand resulted in 1:1 and 2:1 complexes in which the uranyl–oxacalix[3]arene moiety acts as a recognition site for the [2.2.2]cryptand [64]. Figure 19 shows the crystal structure of the 2:1

Catalysis: transition-state molecular recognition?

• Ian H. Williams

Beilstein J. Org. Chem. 2010, 6, 1026–1034, doi:10.3762/bjoc.6.117

• (= ΔERstabilise + ΔERcompress) < ΔETbind ( = ΔETstabilise + ΔETcompress) leading to net TS stabilisation. Later we proposed [16] a more realistic catalyst design for methyl transfer in the shape of inside-methylated [1.1.1]cryptand (Scheme 2). B3LYP/6-31G* calculations predicted the inter-bridgehead N…N distance

• in cryptand (b) to be 0.75 Å shorter than in the ion-molecule complex between trimethylamine and tetramethylammonium (a), indicating compression along the N…C…N axis, but more significantly the corresponding difference in the corresponding transition structures was only 0.35 Å. In other words, the

• catalysed by COMT. SN2 methyl transfer (a) uncatalysed and (b) within a cryptand cavity. Formation of glycosyl-enzyme covalent intermediate COV. Acknowledgements I am grateful to Professor T. M. Krygowski for the invitation to present this material at the Central European School on Physical Organic

Molecular recognition of organic ammonium ions in solution using synthetic receptors

• Andreas Späth and
• Burkhard König

Beilstein J. Org. Chem. 2010, 6, No. 32, doi:10.3762/bjoc.6.32

• ]. This argument holds for polyether compounds with two podand arms, bibraccial lariat ethers. Bridging the ring with the arm leads to cryptands, bicyclic (10a) or polycyclic (10b) crown ethers [115]. If the moiety is “tricyclic closed” via the two nitrogen atoms, the resulting cryptand 10a permits cation

• encapsulation [116] (Figure 7). On inclusion in the cavity of the cryptand, the guest is shielded by three or more polyether bridges. As a result of this encapsulation, cryptands form more stable complexes than coronands (Ka = 106 for NH4+ in methanol at 25 °C). In addition, solution thermodynamics of amino

• acids with 4 and 10a confirm these facts [117]. Macrotricyclic cryptand 10b exhibits a substantial enhancement in ammonium vs. potassium ion selectivity in comparison to crown and azacrown ethers, as determined by both calorimetric [104] and NMR studies [118]. The high selectivity over potassium ions

Structural studies on encapsulation of tetrahedral and octahedral anions by a protonated octaaminocryptand cage

• I. Ravikumar,
• P. S. Lakshminarayanan,
• E. Suresh and
• Pradyut Ghosh

Beilstein J. Org. Chem. 2009, 5, No. 41, doi:10.3762/bjoc.5.41

• C–H···F hydrogen bonds with [H8L1]8+. In the cases of complexes 2 and 3, the cryptand L1 in octaprotonated state shows monotopic encapsulation of the guest and the final conformation of these receptors is spherical in nature compared to the elongated shape of hexaprotonated state of L1 in complex 1

• . Keywords: anion receptor; cryptand; molecular recognition; proton cage; Introduction In recent years considerable efforts have been made in elucidating the coordination chemistry of anions because of their vital roles in biological systems [1], medicine [2], catalysis [3], and environmental issues [4

• ···X− interactions [34]. In this article we report solid state structural evidence of encapsulation and binding of tetrahedral oxyanions ClO4− and HSO4− as well as encapsulation of octahedral anion HSiF6− with L1 in different protonated states. Results and Discussion Syntheses. The cryptand L1 was