The activity of indenylidene derivatives in olefin metathesis catalysts

• Maria Voccia,
• Steven P. Nolan,
• Luigi Cavallo and
• Albert Poater

Beilstein J. Org. Chem. 2018, 14, 2956–2963, doi:10.3762/bjoc.14.275

• the phosphine release, and the relative stability of the corresponding metallacycle over classical ylidene ligands. Mayer bond orders and steric maps provide structural reasons for these effects, whereas NICS aromaticity and conceptual DFT confirm that the electronic parameters do not play a

• ]. In order to evaluate the change of the aromaticity of the phenyl ring of the indenylidene derivatives 3–6, we evaluated the aromaticity of the six-membered aryl rings, as well as the ring current on the five-membered ring by means of magnetic-based aromaticity criterion NICS (GIAO, see all NICS

• values in Supporting Information File 1). The 5-membered rings turn out to be non-aromatic, whereas the changes of the aromaticity of the phenyl rings are minimal. Species I, 2 and 3 are 0.151 and 0.083 ppm more aromatic than 1, nearly identical for the IMes systems 5 and 6, 0.166 and 1.117 ppm and more

Synthesis and biological evaluation of 1,2-disubstituted 4-quinolone analogues of Pseudonocardia sp. natural products

• Stephen M. Geddis,
• Teodora Coroama,
• Suzanne Forrest,
• James T. Hodgkinson,
• Martin Welch and
• David R. Spring

Beilstein J. Org. Chem. 2018, 14, 2680–2688, doi:10.3762/bjoc.14.245

• an enamine moiety, these compounds would likely be highly challenging to synthesise by other means. However, it is proposed that the involvement of the nitrogen lone-pair in the aromaticity of the quinolone system attenuates the susceptibility of 14ab and 14bb towards hydrolysis. Intriguingly, 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

• 3Pd is further red-shifted and more intense. Keywords: aromaticity; earring subporphyrin; π-extended; supramolecular chemistry; Findings Since its first synthesis in 2006 [1][2], subporphyrin, the lowest homolog of porphyrins, has received considerable attention [3][4][5][6][7][8] due to its 14π

• bonds in the subporphyrin moiety are of similar lengths (1.383(6)–1.447(5) Å). In contrast, the C–C bond lengths in the tripyrrin moiety alternate (1.341(5)–1.472(5) Å). These data clearly indicate that the subporphyrin moiety remains its aromaticity while the tripyrrin moiety participates in an

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

• system (Scheme 1). Their dipolar resonance structures such as tropylium oxide form 1B and 2B have been reported to provide a Hückel sextet of electrons that is necessary for aromaticity (Scheme 1) [1][2][3][4][5][6][7][8][9]. The tropone core is the ubiquitous structural motif in the alkaloid colchicine

• molecular structure of 4,5-benzotropone (11) was determined by Hata’s group [50]. X-ray diffraction analysis showed that the molecule is approximately planar and the bond alternation in the seven-membered ring and C=O bond length support satisfactory aromaticity. 2.1. Synthesis of 4,5-benzotropone (11

• considerable interest for both theoretical and preparative reasons. The aromaticity of 3,4-benzotropone (13A) is considered to depend on the contribution of electronically polarized form 13B such as tropone 1A (Figure 8) [153][154]. Kurihara’s group reported the calculated resonance energies and bond currents

Mannich base-connected syntheses mediated by ortho-quinone methides

• Petra Barta,
• Ferenc Fülöp and
• István Szatmári

Beilstein J. Org. Chem. 2018, 14, 560–575, doi:10.3762/bjoc.14.43

• aminoalkylphenol derivatives. A few examples are summarized in Table 2. An important difference although must be noted. In the case of aminonalkylnaphthols, the o-QM intermediate partially remains aromatic while the formation of phenolic o-QMs leads to the loss of the aromaticity of the only aromatic ring present

Electron-deficient pyridinium salts/thiourea cooperative catalyzed O-glycosylation via activation of O-glycosyl trichloroacetimidate donors

• Mukta Shaw,
• Yogesh Kumar,
• Rima Thakur and
• Amit Kumar

Beilstein J. Org. Chem. 2017, 13, 2385–2395, doi:10.3762/bjoc.13.236

• possible formation of 1,2-adduct X, on the reaction of 3a with 2a which is eventually responsible for the loss of aromaticity of the pyridinium ring. Based on the outcomes of 1H NMR spectroscopic studies, we started optimizing the reaction conditions. Upon treatment of glycosyl donor 1α and glycosyl

Superstructures with cyclodextrins: Chemistry and applications IV

• Gerhard Wenz

Beilstein J. Org. Chem. 2017, 13, 2157–2159, doi:10.3762/bjoc.13.215

• regioselective introduction of one, two, three or more equal or different substituents starting from the corresponding perbenzyl or permethyl derivatives [11][12]. In this way, hexaphyrine was attached threefold to α-CD to construct superstructures with switchable aromaticity [13]. Furthermore

Fluorescent carbon dots from mono- and polysaccharides: synthesis, properties and applications

• Stephen Hill and
• M. Carmen Galan

Beilstein J. Org. Chem. 2017, 13, 675–693, doi:10.3762/bjoc.13.67

• of nanoparticle formation. Trapping of the iminium electrophile could allow oligomer formation and dehydration, leading to the formation of the sp3-enriched nanocrystalline core. In the second phase of the reaction, following the loss of bulk water, further carbonisation occurs and aromaticity is

Regiochemistry of cyclocondensation reactions in the synthesis of polyazaheterocycles

• Patrick T. Campos,
• Leticia V. Rodrigues,
• Andrei L. Belladona,
• Caroline R. Bender,
• Juliana S. Bitencurt,
• Fernanda A. Rosa,
• Davi F. Back,
• Helio G. Bonacorso,
• Nilo Zanatta,
• Clarissa P. Frizzo and
• Marcos A. P. Martins

Beilstein J. Org. Chem. 2017, 13, 257–266, doi:10.3762/bjoc.13.29

• the loss of heterocyclic aromaticity. However, aiming at the synthesis of new heterocycles, we next investigated the reaction of compounds 5–7 with different 1,2-diamines. Initially, the reaction between compound 5 and ethylenediamine (8a) was tested. Due to precipitation of the product during the

Recent highlights in biosynthesis research using stable isotopes

• Jan Rinkel and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2015, 11, 2493–2508, doi:10.3762/bjoc.11.271

• benzene ring includes intermediate loss of aromaticity followed by rearomatization during the formation of the cyclophane ring [51]. However, a recently investigated example shows, that breaking the aromatic character of a phenyl ring is not necessary for building up a bended aryl ether in a biological

• the phenolic oxygen at C-6 to close the macrocycle in 25. In this mechanism, the aromaticity of the phenol ring remains untouched. Intramolecular Diels–Alder reaction gives rise to the hexacyclic system 26, which would then be oxidized to pyrrocidine A (24) at C-2’. In contrast to route A, the

• aromaticity. This kind of tyrosine reporter might also prove useful in other biosynthetic studies. Sometimes the biosynthesis of mixed PKS/NRPS/FAS natural products involves the discovery of surprising building blocks as recently shown for thiomarinol A (27, Figure 5) from the marine bacterium

Advances in the synthesis of functionalised pyrrolotetrathiafulvalenes

• Luke J. O’Driscoll,
• Sissel S. Andersen,
• Marta V. Solano,
• Dan Bendixen,
• Morten Jensen,
• Troels Duedal,
• Jess Lycoops,
• Cornelia van der Pol,
• Rebecca E. Sørensen,
• Karina R. Larsen,
• Kenneth Myntman,
• Christian Henriksen,
• Stinne W. Hansen and
• Jan O. Jeppesen

Beilstein J. Org. Chem. 2015, 11, 1112–1122, doi:10.3762/bjoc.11.125

• aromaticity occurs: 2 contains a single aromatic, 6 π-electron 1,3-dithiolium system, and 3 possesses two such systems (Figure 1). These oxidations occur at low potential (E11/2 = 0.34 V and E21/2 = 0.73 V vs Ag/AgCl in MeCN [4]) and can be performed sequentially and reversibly. Additionally, both 2 and 3 are

Single-molecule conductance of a chemically modified, π-extended tetrathiafulvalene and its charge-transfer complex with F₄TCNQ

• Raúl García,
• M. Ángeles Herranz,
• Edmund Leary,
• M. Teresa González,
• Gabino Rubio Bollinger,
• Marius Bürkle,
• Linda A. Zotti,
• Yoshihiro Asai,
• Fabian Pauly,
• Juan Carlos Cuevas,
• Nicolás Agraït and
• Nazario Martín

Beilstein J. Org. Chem. 2015, 11, 1068–1078, doi:10.3762/bjoc.11.120

• quite different from pristine TTF. Thus, whereas TTF is mostly planar in the neutral form, exTTF is a highly distorted, out-of-plane molecule with a butterfly shape in its neutral state. It undergoes a dramatic gain of planarity and aromaticity upon oxidation (Figure 1) [18][19]. This gain of stability

Quarternization of 3-azido-1-propyne oligomers obtained by copper(I)-catalyzed azide–alkyne cycloaddition polymerization

• Shun Nakano,
• Akihito Hashidzume and
• Takahiro Sato

Beilstein J. Org. Chem. 2015, 11, 1037–1042, doi:10.3762/bjoc.11.116

• dipole moment and aromaticity, 1,2,3-triazole itself may be a functional group. Polymers composed of dense 1,2,3-triazole moieties on the backbone are thus promising as functional materials. Recently, we have investigated the CuAAC polymerization of 3-azido-1-propyne (AP) using 3-bromo-1-propyne as a

Carboxylated dithiafulvenes and tetrathiafulvalene vinylogues: synthesis, electronic properties, and complexation with zinc ions

• Yunfei Wang and
• Yuming Zhao

Beilstein J. Org. Chem. 2015, 11, 957–965, doi:10.3762/bjoc.11.107

• -donating properties of TTF arise from its aromaticity-stabilized cationic states after releasing one and/or two electrons [1][2][3][4][5][8][9][10]. Tetrathiafulvalene vinylogues (TTFVs) are π-extended analogues of TTF bearing extended vinyl bridges between the two dithiole rings of TTF [9][10][11

Interactions between tetrathiafulvalene units in dimeric structures – the influence of cyclic cores

• Huixin Jiang,
• Virginia Mazzanti,
• Christian R. Parker,
• Søren Lindbæk Broman,
• Jens Heide Wallberg,
• Karol Lušpai,
• Adam Brincko,
• Henrik G. Kjaergaard,
• Anders Kadziola,
• Peter Rapta,
• Ole Hammerich and
• Mogens Brøndsted Nielsen

Beilstein J. Org. Chem. 2015, 11, 930–948, doi:10.3762/bjoc.11.104

• that required to reduce the acyclic TEE compound 1a (−1.70 V vs Fc/Fc+) [10]. We explained this readiness of 2a to accommodate electrons by a gain of aromaticity; a resonance form with a 14 πz core can be drawn for the dianion and a diatropic ring-current was supported by NICS calculations. The new

• an intramolecular origin of the NIR absorptions. Finally, the different radiaannulene cores also present redox-active units, undergoing reversible and ready reductions, which we ascribe to some gain in aromaticity upon reduction. On account of these electron-accepting properties, the neutral TTF

Enhancing the reactivity of 1,2-diphospholes in cycloaddition reactions

• Almaz Zagidullin,
• Vasili Miluykov,
• Elena Oshchepkova,
• Artem Tufatullin,
• Olga Kataeva and
• Oleg Sinyashin

Beilstein J. Org. Chem. 2015, 11, 169–173, doi:10.3762/bjoc.11.17

• : cycloaddition; phospholes; phosphorus heterocycles; polycyclic phosphines; retro-Diels–Alder reaction; Introduction Phospholes are weakly aromatic heterocycles and demonstrate rather different properties from those of their S, N and O counterparts [1][2]. Due to low their aromaticity, phospholes are of

• , phosphinidenes, etc. [2]. At the same time, the presence of electron-withdrawing substituents (cyano-, alkoxy-, or halo-) at the phosphorus atom reduces the aromaticity of the monophosphole ring and facilitates cycloaddition reactions resulting in novel 7-phosphanorbornenes [5][6], which was verified by

Photorelease of phosphates: Mild methods for protecting phosphate derivatives

• Sanjeewa N. Senadheera,
• Abraham L. Yousef and
• Richard S. Givens

Beilstein J. Org. Chem. 2014, 10, 2038–2054, doi:10.3762/bjoc.10.212

• ground state biradicaloid or zwitterion is the product determining step. In both cases, the aromaticity of both rings is lost upon formation of the Favorskii cyclopropanone intermediates 38 and 41. However, this rationale also falls short because the reactions of the similar biradicaloid or zwitterion

Synthetic scope and DFT analysis of the chiral binap–gold(I) complex-catalyzed 1,3-dipolar cycloaddition of azlactones with alkenes

• María Martín-Rodríguez,
• Luis M. Castelló,
• Carmen Nájera,
• José M. Sansano,
• Olatz Larrañaga,
• Abel de Cózar and
• Fernando P. Cossío

Beilstein J. Org. Chem. 2013, 9, 2422–2433, doi:10.3762/bjoc.9.280

• point of the oxazoline [42]. The NICS value of −7.3 ppm pointed to the aromaticity of that ring in Ylide I. These results explain the existence of different regioselectivities for both ylides. Following the same calculation patterns previously shown for the reaction with NPM, the results of the main

Cyclization of substitued 2-(2-fluorophenylazo)azines to azino[1,2-c]benzo[d][1,2,4]triazinium derivatives

• Aleksandra Jankowiak,
• Emilia Obijalska and
• Piotr Kaszynski

Beilstein J. Org. Chem. 2013, 9, 1873–1880, doi:10.3762/bjoc.9.219

• between the three parent azoazines can be explained with lower aromaticity of the pyrazine ring [15], and with the electropositive character of the N(1) position of the pyrimidine ring, when compared to the pyridine analogue. These two factors may also contribute to the higher reactivity of cations 2 and

Computational study of the rate constants and free energies of intramolecular radical addition to substituted anilines

• Andreas Gansäuer,
• Meriam Seddiqzai,
• Tobias Dahmen,
• Rebecca Sure and
• Stefan Grimme

Beilstein J. Org. Chem. 2013, 9, 1620–1629, doi:10.3762/bjoc.9.185

• k can be ascribed to the lower HOMO–SOMO gap and hence more favorable polar effects for 1. For 2 having the highest rate constant this is not the case. We suggest that the electron withdrawing substituent on N reduces the aromaticity of the aniline and hence facilitates radical attack. For 1 and 2

Selective copper(II) acetate and potassium iodide catalyzed oxidation of aminals to dihydroquinazoline and quinazolinone alkaloids

• Matthew T. Richers,
• Chenfei Zhao and
• Daniel Seidel

Beilstein J. Org. Chem. 2013, 9, 1194–1201, doi:10.3762/bjoc.9.135

• , deoxyvasicinone (4) was obtained as the major product in a process that involved demethylation (Scheme 1, reaction 1). The demethylation of aminals has been previously reported in cases where the product achieves aromaticity [49][50][51], which is presumably the driving force for this transformation. Aminal 30

Interplay of ortho- with spiro-cyclisation during iminyl radical closures onto arenes and heteroarenes

• Roy T. McBurney and
• John C. Walton

Beilstein J. Org. Chem. 2013, 9, 1083–1092, doi:10.3762/bjoc.9.120

• important for the success of many heterocycle syntheses. Spiro-cyclisations of iminyls lead to formation of strained quaternary C-atoms, and the spiro-intermediates have no straightforward reaction channel for return to aromaticity. The process might be reversible, depending on the architecture of the chain

• and the extent of strain in the spiro-radical. On the other hand ortho-cyclisations can easily be followed by return to aromaticity of the cyclohexadienyl radicals, either by transfer out of the labile H-atom, or by transfer of an electron to a suitable sink with generation of the corresponding

Photoionisation of the tropyl radical

• Kathrin H. Fischer,
• Patrick Hemberger,
• Andras Bodi and
• Ingo Fischer

Beilstein J. Org. Chem. 2013, 9, 681–688, doi:10.3762/bjoc.9.77

• the focus of research since the 1960s [3][4] due to their symmetry properties. The interest originated in the expected stability of the tropyl cation, which is an aromatic molecular ion according to the Hückel rules. The aromaticity was confirmed and the symmetry of the C7H7+ established as D7h [5

Molecular solubilization of fullerene C₆₀ in water by γ-cyclodextrin thioethers

• Hai Ming Wang and
• Gerhard Wenz

Beilstein J. Org. Chem. 2012, 8, 1644–1651, doi:10.3762/bjoc.8.188

• modification of C60. The regioselectivity of derivatization is difficult to control [15], and derivatization reduces aromaticity, which leads to a change of the distinct electronic and photonic properties of C60. Dispersions of C60 nanoparticles in water have been discussed as alternatives for molecular

A quantitative approach to nucleophilic organocatalysis

• Herbert Mayr,
• Sami Lakhdar,
• Biplab Maji and
• Armin R. Ofial

Beilstein J. Org. Chem. 2012, 8, 1458–1478, doi:10.3762/bjoc.8.166

• -imidazoline relative to 2-benzylidene-imidazolidine is explained by the gain of aromaticity during electrophilic additions to the imidazoline derivatives. O-Methylated Breslow intermediates are a hundred-fold less nucleophilic than deoxy Breslow intermediates. Keywords: enamine activation; iminium activation

• chemical shifts (NICS) [109][110][111], which are considered to be a measure of aromaticity. In agreement with the almost equal lengths of the exocyclic C–C bonds in 45a (136.1 pm) and 45c (135.4 pm), as determined by X-ray crystallography, none of the two heterocyclic rings in 47a and 47c shows aromatic

• affinity of 47a, can thus be explained by the gain of aromaticity during electrophilic attack. The same line of arguments can be used to rationalize the higher nucleophilicities and basicities of the triazoline derivatives 45b and 47b, respectively [107]. As the unsaturated carbenes 49a and 49b have