A heteroditopic macrocycle as organocatalytic nanoreactor for pyrroloacridinone synthesis in water

• Piyali Sarkar,
• Sayan Sarkar and
• Pradyut Ghosh

Beilstein J. Org. Chem. 2019, 15, 1505–1514, doi:10.3762/bjoc.15.152

• Piyali Sarkar Sayan Sarkar Pradyut Ghosh School of Chemical Sciences, Indian Association for the Cultivation of Science, 2A & 2B Raja S.C Mullick Road, Kolkata-700032, India 10.3762/bjoc.15.152 Abstract A heteroditopic macrocycle is reported as an efficient organocatalytic nanoreactor for the

• synthesis of diversely functionalized pyrroloacridinones in aqueous medium. A library of compounds was synthesized in a one-step pathway utilizing 10 mol % of the nanoreactor following a sustainable methodology in water with high yields. Keywords: heteroditopic macrocycle; organocatalyst; nanoreactor

• aggregation tendency. Herein we have extensively explored a multifunctional macrocycle (BATA-MC), comprising bis-amide and tris-amine functionalities as H-bond donor/acceptor moieties, and parallel benzene moieties for aromatic π–π stacking interactions as an organocatalytic nanoreactor for organic

Synthesis and biological evaluation of truncated derivatives of abyssomicin C as antibacterial agents

• Leticia Monjas,
• Peter Fodran,
• Johanna Kollback,
• Carlo Cassani,
• Thomas Olsson,
• Maja Genheden,
• D. G. Joakim Larsson and
• Carl-Johan Wallentin

Beilstein J. Org. Chem. 2019, 15, 1468–1474, doi:10.3762/bjoc.15.147

• truncated derivatives of AbC to harbor activity against Gram-positive bacteria are that the 11-membered ring is intact and that this macrocycle is equipped with an enone functionality [4][5]. In accordance with these previous findings, compounds 4 and 5 were found not to inhibit the growth of any of the

2,3-Dibutoxynaphthalene-based tetralactam macrocycles for recognizing precious metal chloride complexes

• Li-Li Wang,
• Yi-Kuan Tu,
• Huan Yao and
• Wei Jiang

Beilstein J. Org. Chem. 2019, 15, 1460–1467, doi:10.3762/bjoc.15.146

• sidewalls have been synthesized and characterized. The macrocycle containing isophthalamide bridges can bind square-planar chloride coordination complexes of gold(III), platinum(II), and palladium(II) in CDCl3, while the macrocycle with 2,6-pyridine dicarboxamide bridging units cannot. This may be due to

• the shrunken cavity caused by intramolecular hydrogen bonds in the latter tetralactam macrocycle. The binding of the isophthalamide-based macrocycle is mainly driven by hydrogen bonds and electrostatic interactions. This naphthalene-based macrocycle has similar binding affinities to all the three

• abovementioned precious metal chloride complexes. This is in contrast to the fact that the tetralactam macrocycle with anthracene as the sidewalls only show good binding affinities to AuCl4−. The superior binding to all three complexes may be due to the conformational diversity of the naphthalene-based

Reaction of oxiranes with cyclodextrins under high-energy ball-milling conditions

• László Jicsinszky,
• Federica Calsolaro,
• Katia Martina,
• Fabio Bucciol,
• Maela Manzoli and
• Giancarlo Cravotto

Beilstein J. Org. Chem. 2019, 15, 1448–1459, doi:10.3762/bjoc.15.145

• make the formation of (oligo)propylene glycol (oligo-PGs) unavoidable. Moreover, at higher degree of substitution (DS, number of substituent/macrocycle) the HP moiety can be further substituted, giving oligo-PG sidechains on the CDs [6]. At low DS values, occasional residual unsubstituted CDs can be

Introduction of an isoxazoline unit to the β-position of porphyrin via regioselective 1,3-dipolar cycloaddition reaction

• Xiujun Liu,
• Xiang Ma and
• Yaqing Feng

Beilstein J. Org. Chem. 2019, 15, 1434–1440, doi:10.3762/bjoc.15.143

• [15][16][17][18][19][20][21][22][23][24]. Among them, the 1,3-dipolar cycloaddition reaction [25] is an efficient method to fuse five-membered rings on the periphery of the porphyrin framework. Because the periphery double bonds of the porphyrin macrocycle are nice dipolarophiles, and can trap 1,3

• spectrum of 3b. Based on these, the cycloaddition reaction should take place on the β-vinyl group but not the double bond on the porphyrin framework, indicating the high activity of the β-vinyl group over the double bond on the macrocycle. However, at which position of the newly formed isoxazoline is

• nitrile oxide to approach the double bond from outside the macrocycle. In addition, a pair of enantiomers is revealed which formed a dimeric fashion with the help of the fifth coordination to the Zn2+ by the carbonyl group from the other molecule. The distance of Zn–O is found to be 2.37 Å, which is

Bambusuril analogs based on alternating glycoluril and xylylene units

• Tomáš Lízal and
• Vladimír Šindelář

Beilstein J. Org. Chem. 2019, 15, 1268–1274, doi:10.3762/bjoc.15.124

• which can interact with cationic, anionic or neutral guest molecules. Here we present the design and synthesis of a new hybrid macrocycle containing glycoluril and aromatic units. The reaction afforded a mixture of macrocyclic homologues from which a two-membered macrocycle was isolated as the main

• product. Two disastereomers of the macrocycle were separated and characterized by means of NMR spectroscopy and X-ray crystallography. Conformational changes of these diastereomers were investigated using DFT models and variable-temperature NMR. Keywords: bambusurils; conformers; glycolurils; macrocycles

• with chromophore groups on their portals. However, the changes in the absorption spectra of these receptors upon anion binding were negligible since the groups on the portals were too distant from the anion binding site in the center of macrocycle. A different approach for the preparation of UV–vis

Steroid diversification by multicomponent reactions

• Leslie Reguera,
• Cecilia I. Attorresi,
• Javier A. Ramírez and
• Daniel G. Rivera

Beilstein J. Org. Chem. 2019, 15, 1236–1256, doi:10.3762/bjoc.15.121

• promise for the future development of peptide pharmaceuticals. 5 Multicomponent synthesis of steroidal macrocycles and cages Since the beginning of this century, the field of macrocycle synthesis has witnessed the emergence of MCRs as effective ring closing procedures, including the cyclization of large

• , Wessjohann’s group exploited the MiBs strategy based on the Ugi-4CR for the assembly of topologically diverse steroidal macrocycles incorporating a variety of (seco)steroid skeletons [70][71][72]. Probably the highest level of macrocycle complexity achieved in one-pot can be found in the multicomponent

• with a biaryl ether diisocyanide and two equivalents of paraformaldehyde and a monoprotected diamine. After the initial macrocyclization, steroidal macrocycle 71 was deprotected by removal of the Cbz groups and subsequently submitted to a second multicomponent macrocyclization protocol – in this case

Self-assembly behaviors of perylene- and naphthalene-crown macrocycle conjugates in aqueous medium

• Xin Shen,
• Bo Li,
• Tiezheng Pan,
• Jianfeng Wu,
• Yangxin Wang,
• Jie Shang,
• Yan Ge,
• Lin Jin and
• Zhenhui Qi

Beilstein J. Org. Chem. 2019, 15, 1203–1209, doi:10.3762/bjoc.15.117

• -assembly behavior in various solvents was investigated particularly in aqueous medium, due to the recently discovered hydrophilic properties of B21C7 crown macrocycle. An unexpected fluorescence quenching phenomenon was observed in the PDI-B21C7 macrocycle conjugate in chloroform. The detailed UV–vis

• absorption and fluorescence spectra of these PDI/NDI derivatives in different solvents as well as their morphologies were investigated. Keywords: aqueous medium; crown ether; macrocycle; perylene diimide derivative; self-assembly; Introduction Owing to their unique physicochemical properties, self

• , little was known to the self-assembly behaviors of B21C7 crown macrocycle functionalized PDIs/NDIs in aqueous solution, even though there have been several reports about crown ether-functionalized PDIs or NDIs, which mostly focused on their interactions with metal ions [82][83][84][85]. Herein, we

Molecular recognition using tetralactam macrocycles with parallel aromatic sidewalls

• Dong-Hao Li and
• Bradley D. Smith

Beilstein J. Org. Chem. 2019, 15, 1086–1095, doi:10.3762/bjoc.15.105

• following sections, we divide the guest structures into two large categories; those that associate with a tetralactam host in a reversible solution-state equilibrium and those that are permanently trapped inside a tetralactam macrocycle as an interlocked rotaxane or catenane. It is important to emphasize

• groups led by Jurczak [15], Bowman-James [20], Lüning [21], and Thordarson [22]). 2. Macrocyclic structure and amphiphilic cavity The peripherally appended Z groups on the bridging units in each macrocycle determine the solubility in different media without directly impacting the guest recognition within

• factors is reversed; hydrogen bonding is relatively weak and strong guest association occurs when hydrophobic sections of a complementary guest are able to contact the hydrophobic interior surfaces of the two aromatic sidewalls [26]. The first macrocycle system in Scheme 1 to be studied in detail was

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

• combination of two isocyanide-based multicomponent reactions (azido-Ugi and Passerini reactions) allowed easy access to a library of macrocyclic depsipeptides in only four steps with variations in the size of the macrocycle as well as in the side chains (Scheme 15). This was the first example in which the

• was cyclized in good yield to macrocycle 93 via an intramolecular Ugi three-component four-center reaction (U-3C-4CR). In the continuation of our studies, we used a similar strategy for the combination of consecutive isocyanide-based multicomponent reactions (Ugi and Passerini reactions) [34]. This

• different C-protected amino acids (120–122) with diisocyanide 116 and diacid 119. The approach allowed the one pot obtention of six different macrocycles and a macrocycle core system containing two symmetrical building blocks. This same strategy has also been carried out for the synthesis of natural

Mechanochemistry of supramolecules

• Anima Bose and
• Prasenjit Mal

Beilstein J. Org. Chem. 2019, 15, 881–900, doi:10.3762/bjoc.15.86

• of the rotaxane system via pseudorotaxane 18. A shorter reaction time, use of small amounts of solvent and the high yield were the advantages over the solvent-mediated synthesis [62]. Macrocycle synthesis The mechanochemical synthesis of sphere-like nanostructures was reported by Severin and co

• -Bu2Si(OH)2, borasiloxane-based macrocycle 23 was obtained in >90% yield after 2 × 45 min of grinding [65]. In 2017, Xu and his group developed the first method towards the synthesis of 2-dimensional aromatic polyamides (2DAPAs) under solvent-free ball-milling conditions [66]. Reacting 1,3,5

• ][92]. The mechanochemical milling of a 1:1 mixture of paraformaldehyde and (R,R)-hexahydro-2-benzimidazolinone along with a small amount of concentrated aqueous HCl for 30–60 min followed by aging at 45 °C for 6 days, resulted in the formation of six-membered macrocycle cycHC[6] 35 with 98% conversion

Coordination chemistry and photoswitching of dinuclear macrocyclic cadmium-, nickel-, and zinc complexes containing azobenzene carboxylato co-ligands

• Jennifer Klose,
• Tobias Severin,
• Peter Hahn,
• Alexander Jeremies,
• Jens Bergmann,
• Daniel Fuhrmann,
• Jan Griebel,
• Bernd Abel and
• Berthold Kersting

Beilstein J. Org. Chem. 2019, 15, 840–851, doi:10.3762/bjoc.15.81

• + fragment in solution, as in [Cd2L(μ-Cl)]+ and other carboxylato-bridged Cd2 complexes supported by this macrocycle [10][12]. The remaining four signals (two doublets and one singlet for aromatic and one singlet for aliphatic CH3 protons) can be attributed to the azobenzene co-ligand. These were readily

• [Cd2L]2+ fragment. The switch from the trans to the cis form induces significant change of the π–π transitions of the supporting N6S2 macrocycle, which may be indicative of some increased π–π- (or charge transfer) interactions between the aromatic rings of the electron rich amino thiophenolato

• macrocycle and the electron poor azobenzene-carboxylato ligands. There are little, if any, differences in the time-scales for thermal relaxation of the free and Cd-bound azobenzene-carboxylate systems, suggesting that the cavity of [Cd2L]2+ does not sterically constrain the photoisomerization process

Homo- and hetero-difunctionalized β-cyclodextrins: Short direct synthesis in gram scale and analysis of regiochemistry

• Gábor Benkovics,
• Mihály Bálint,
• Éva Fenyvesi,
• Erzsébet Varga,
• Szabolcs Béni,
• Konstantina Yannakopoulou and
• Milo Malanga

Beilstein J. Org. Chem. 2019, 15, 710–720, doi:10.3762/bjoc.15.66

• defined positions on the CD macrocycle in an efficient, reproducible and up-scalable process is still a very challenging task. In order to achieve homo-difunctionalization of the primary side, two synthetic approaches can be applied: (i) the direct difunctionalization, based on the regioselective

Design, synthesis and spectroscopic properties of crown ether-capped dibenzotetraaza[14]annulenes

• Krzysztof M. Zwoliński and
• Julita Eilmes

Beilstein J. Org. Chem. 2019, 15, 617–622, doi:10.3762/bjoc.15.57

• -ATR, 1H and 13C NMR spectroscopy and elemental analysis. Keywords: crown ether; dibenzotetraaza[14]annulene; DBTAA; macrocycle; Schiff base; Introduction The design and synthesis of novel polycyclic receptor architecture is of fundamental importance, since model recognition studies contribute to

• showed cation and solvent-induced dimerisation. More recently, Raston et al. reported the synthesis of Goedken’s macrocycle tmtaa nickel(II) complex featuring a single oligo(ethylene glycol) chain strapped across the face of the DBTAA macrocyclic core [28]. However, to the best of our knowledge, there

• chloroform and methanol (1:1, v/v). The third, main band, was eluted isocratically with a mixture of CHCl3/MeOH/NH3aq (10:10:1, v/v/v), evaporated to dryness under reduced pressure, and kept in a vacuum overnight at ambient temperature to remove all volatiles. Crown ether-capped DBTAA macrocycle 3a: [7,16

Synthesis of the polyketide section of seragamide A and related cyclodepsipeptides via Negishi cross coupling

• Jan Hendrik Lang and
• Thomas Lindel

Beilstein J. Org. Chem. 2019, 15, 577–583, doi:10.3762/bjoc.15.53

• endeavour, a new synthesis of the polyketide section present in seragamides and most of jasplakinolides and geodiamolides. We also include the synthesis of the protected tripeptide section of seragamide A (2), even if the macrocycle still remains to be assembled. Seragamide A (2) from the marine sponge

Design of indole- and MCR-based macrocycles as p53-MDM2 antagonists

• Constantinos G. Neochoritis,
• Maryam Kazemi Miraki,
• Eman M. M. Abdelraheem,
• Ewa Surmiak,
• Tryfon Zarganes-Tzitzikas,
• Beata Łabuzek,
• Tad A. Holak and
• Alexander Dömling

Beilstein J. Org. Chem. 2019, 15, 513–520, doi:10.3762/bjoc.15.45

• ]. Herein, an indole-based macrocycle synthesis is reported in a one-pot fashion based on Ugi macrocyclization with readily available α,ω-amino acids. Moreover, in continuation of our efforts in the design and synthesis of macrocycles targeting the p53–MDM2 interaction demonstrating the potential of these

• . The aforementioned artificial macrocycles combine the indole ring, a motif found in many bioactive molecules with the drug-like properties of a non-peptide macrocycle. We hypothesize that these chimeric derivatives of an indole and a macrocycle will offer new potential on specific PPIs and other

• postgenomic targets as it was demonstrated with the p53-MDM2 interaction. (A) Modeling of the macrocycle 2h (cyan sticks) and 2n (magenta sticks) into the MDM2 receptor (PDB ID: 1YCR); (B) 2D structure of 2h with the substituents targeting the subpockets of MDM2; (C) Analysis of the synthesized macrocycles

Chemical structure of cichorinotoxin, a cyclic lipodepsipeptide that is produced by Pseudomonas cichorii and causes varnish spots on lettuce

• Hidekazu Komatsu,
• Takashi Shirakawa,
• Takeo Uchiyama and
• Tsutomu Hoshino

Beilstein J. Org. Chem. 2019, 15, 299–309, doi:10.3762/bjoc.15.27

• . Figure S19B indicates that the necrotic lesions caused by the monoacetate (3) were somewhat less severe, but the compound was still active; the tetraacetate (4) showed almost no activity. For the monoacetate (3), the hydrophilic NH2 of Dab20, which is one of the residues in the macrocycle of the peptide

• is likely that the hydrophilic Ser21, embedded in the macrocycle of the peptide, is crucial for the necrosis activity. The peptides in the macrocycle, listed in Supporting Information File 1, Figure S15, consist of 5 or 8 amino acids, and of these, at least two of the hydrophilic amino acids are

• . Compound B has a macrocycle composed of 4-amino acids, but it exhibited no necrotic activity. As seen in the structures of all the toxins depicted in Figure S15 (Supporting Information File 1), the macrocycles are in terminal positions; thus, having the macrocycle at the termini may be required for the

Nucleoside macrocycles formed by intramolecular click reaction: efficient cyclization of pyrimidine nucleosides decorated with 5'-azido residues and 5-octadiynyl side chains

• Jiang Liu,
• Peter Leonard,
• Sebastian L. Müller,
• Constantin Daniliuc and
• Frank Seela

Beilstein J. Org. Chem. 2018, 14, 2404–2410, doi:10.3762/bjoc.14.217

• functionalized at the 5-position of the nucleobase with octadiynyl side chains and with azido groups at the 5’-position of the sugar moieties were synthesized. The macrocycles display freely accessible Watson–Crick recognition sites. The conformation of the 16-membered macrocycle was deduced from X-ray analysis

• intramolecular cyclization to a macrocycle was not observed. Next, the 5’-azido compound 2 was employed in the copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) "click" reaction [38][39] to build up macrocycle 3. In this regard, two reaction pathways have to be considered: (i) an intramolecular “click

• ” reaction leading to a macrocycle or (ii) an intermolecular “click” reaction forming dimeric or oligomeric compounds. For a deeper insight, the “click” reaction was executed under different reaction conditions. First, the copper(I)-promoted “click” reaction was performed on 2 in the presence of copper(II

Synthesis and post-functionalization of alternate-linked-meta-para-[2ⁿ.1ⁿ]thiacyclophanes

• Wout De Leger,
• Koen Adriaensen,
• Koen Robeyns,
• Luc Van Meervelt,
• Joice Thomas,
• Björn Meijers,
• Mario Smet and
• Wim Dehaen

Beilstein J. Org. Chem. 2018, 14, 2190–2197, doi:10.3762/bjoc.14.192

• , entries 2, 3, 9, and 10). Interestingly, stronger bases let to the almost exclusive formation of the [3 + 3] adduct 7 (Table 1, entry 3) over [2 + 2] adduct 6. A higher proportion of macrocycle 6 was obtained using K2CO3 as the base and toluene as the solvent, the yield rose from 14% (Table 1, entry 2) to

• yield of 91%. The 3D structure of macrocycle 6 was confirmed by single crystal X-ray diffraction and shows approximate twofold rotational symmetry (point group C2, Figure 1). The dihedral angles between the aromatic rings are given in Table S2 (Supporting Information File 1, ring numbering as shown in

• -elimination (route B) can easily occur, leading to reversal of the addition reactions. This was observed in a stability experiment where pure [3 + 3] macrocycle 7 in CDCl3 (without adding base) over two weeks’ time converted into a mixture of [3 + 3] macrocycle 7 (9%), acyclic oligomers (50%) and the more

Tetrathiafulvalene – a redox-switchable building block to control motion in mechanically interlocked molecules

• Hendrik V. Schröder and
• Christoph A. Schalley

Beilstein J. Org. Chem. 2018, 14, 2163–2185, doi:10.3762/bjoc.14.190

• derivatives I and J [55][56][57]. The incorporation of these symmetric species into MIMs often circumvents complex isomeric mixtures. 3. Pseudorotaxanes and inclusion complexes: on the way to TTF-based MIMs Pseudorotaxanes have the general form of a molecular thread encircled by a macrocycle. The difference

• -cationic form since the association energy of the donor–acceptor complex must be overcome. After oxidation, the radical-cation 1●+ is expelled from host 3 by repulsive Coulombic forces. If 1●+ gets further oxidized to the π-electron-poor dication 12+, the π-electron-rich macrocycle 8 can now encapsulate

• easily a reversible molecular motion can be achieved by redox-switching of the TTF unit. 4. Rotaxanes Rotaxanes consist of a dumbbell-shaped axle molecule encircled by a macrocycle. Bulky stopper groups at both ends of the axle prevent a deslipping of the wheel. With a development starting from low

Calix[6]arene-based atropoisomeric pseudo[2]rotaxanes

• Carmine Gaeta,
• Carmen Talotta and
• Placido Neri

Beilstein J. Org. Chem. 2018, 14, 2112–2124, doi:10.3762/bjoc.14.186

• I*, Figure 1) consisting of achiral components. The combination of a macrocycle with rotational asymmetry and a directional thread with non-equivalent ends is the cause of chirality in this example (Figure 1). Interestingly, our group showed that a chiral pseudorotaxane can be generated upon

• chemical shift of the ArCH2Ar methylene C, which is 30–33 ppm for the syn-orientation of the proximal phenol rings and typically 36–39 ppm with anti-positioned phenol rings as in alternate conformations. As exemplified above, the calix[6]arene macrocycle has been widely used as wheel for the assembly of

• +·TFPB− and 3+·TFPB− salts is outlined in Scheme 1, while calix[6]arene 1 was obtained following a known procedure [40]. The 1H NMR spectrum of hexahexyloxycalix[6]arene 1 in CDCl3 at 298 K shows broad ArCH2Ar signals indicative of a conformational mobility of the macrocycle in which the inversion

A switchable [2]rotaxane with two active alkenyl groups

• Xiu-Li Zheng,
• Rong-Rong Tao,
• Rui-Rui Gu,
• Wen-Zhi Wang and
• Da-Hui Qu

Beilstein J. Org. Chem. 2018, 14, 2074–2081, doi:10.3762/bjoc.14.181

• and thiol functional groups. The reversible shuttling movement of the macrocycle between two different recognition sites on the molecular thread can be driven by external acid and base. This kind of rotaxane bearing functional groups provides a powerful platform for preparing stimuli-responsive

• design, synthesis, characterization and shuttling motion of a [2]rotaxane R1, which is modified with two naked alkenyl bonds. In this [2]rotaxane, a functional dibenzo-24-crown-8 (DB24C8) macrocycle is interlocked with an flexible chain and could perform reversible shuttling between two different

• ]rotaxane R1, the DB24C8 macrocycle is functionalized with an alkenyl unit on one of the benzene groups. Two distinguishable recognition sites, a dibenzylammonium (DBA) and an amide binding site, are introduced to the axle and linked with a long alkyl chain. The amide moiety could act as another combining

Coordination-driven self-assembly vs dynamic covalent chemistry: versatile methods for the synthesis of molecular metallarectangles

• Li-Li Ma,
• Jia-Qin Han,
• Wei-Guo Jia and
• Ying-Feng Han

Beilstein J. Org. Chem. 2018, 14, 2027–2034, doi:10.3762/bjoc.14.178

• assemblies 3a and 3b. The optimized structures of each assembly featured a similar rectangular metallacyclic macrocycle structure (Figure 4). The sizes of the assembled structures were estimated to be 26.3 × 5.6 Å (3a) and 20.1 × 5.6 Å (3b). Conclusion In summary, a modular protocol for the synthesis of

Synthesis of new p-tert-butylcalix[4]arene-based polyammonium triazolyl amphiphiles and their binding with nucleoside phosphates

• Vladimir A. Burilov,
• Guzaliya A. Fatikhova,
• Mariya N. Dokuchaeva,
• Ramil I. Nugmanov,
• Diana A. Mironova,
• Pavel V. Dorovatovskii,
• Victor N. Khrustalev,
• Svetlana E. Solovieva and
• Igor S. Antipin

Beilstein J. Org. Chem. 2018, 14, 1980–1993, doi:10.3762/bjoc.14.173

• solutions. Results and Discussion Synthesis of polyammonium calix[4]arene derivatives The functionalization of calix[4]arenes with azide groups paves the way to introduce a wide variety of functional groups [27] on the upper rim of the macrocycle by, e.g., the copper-catalyzed azide–alkyne cycloaddition

• highly explosive [29]. Usually azide groups are installed in the upper rim of the macrocycle by a chloromethylation reaction and subsequent nucleophilic substitution by azide anions [30][31] forming rather flexible azidomethyl fragments. In this investigation more rigid arylazide calixarene derivatives

• , correspondingly. The structures of the final products were established by 2D 1H-1H NOESY NMR. For example, in the case of macrocycle 10b (Figure 2) the cross-peaks between signals of neighboring aromatic protons (δ = 7.32 and 7.92 ppm) indicate a cone stereoisomeric form of the macrocycle. Moreover, the

Synthesis and characterization of π–extended “earring” subporphyrins

• Haiyan Guan,
• Mingbo Zhou,
• Bangshao Yin,
• Ling Xu and
• Jianxin Song

Beilstein J. Org. Chem. 2018, 14, 1956–1960, doi:10.3762/bjoc.14.170

• antiaromatic character of the ear-containing macrocycle, which is quite similar to the analogous “earring” porphyrin [38]. Furthermore, the antiaromaticity of the ear-containing macrocycle is proved by the large positive NICS value in the hole as well as the anticlockwise ring currency (see Supporting