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Search for "aromaticity" in Full Text gives 70 result(s) in Beilstein Journal of Organic Chemistry.
Synthetic scope and DFT analysis of the chiral binap–gold(I) complex-catalyzed 1,3-dipolar cycloaddition of azlactones with alkenes
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
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
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
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
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
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
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
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
Cation affinity numbers of Lewis bases
Beilstein J. Org. Chem. 2012, 8, 1406–1442, doi:10.3762/bjoc.8.163
- , indicating a negligible influence of ring aromaticity. The influence of the ring substituents on MCA values is less systematic and depends on the ring system at hand. For all systems, however, the largest MCA values are obtained for mesityl substituents. Mayr and co-workers have determined nucleophilicity
On the control of secondary carbanion structure utilising ligand effects during directed metallation
Beilstein J. Org. Chem. 2012, 8, 50–60, doi:10.3762/bjoc.8.5
- the planarity of the deprotonated carbon centre and the bonding pattern in the organic anion seen in the PMDTA complex are retained. DFT analysis corroborates both the short distance between aromatic ring and carbanion centre and the unperturbed nature of aromaticity in 6-Lil·L (L = Lewis base). The
- exhibiting pentadienyl character) is not replicated in 6-Lil·PMDTA. Instead, combined with the planarity of the ring system observed here, bond lengths in 6-Lil·PMDTA suggest the retention of aromaticity. Consistent with this, a torsion of only 6.1(3)° between directing and deprotonated groups (C(=O)–C–C–C
- ], phosphino- [47][48][49], thio-/sulfamido-/sulfimido- [50][51][52][53] and silylbenzyl anions [54][55][56][57][58][59][60][61][62], have all demonstrated long aryl–(α-C) distances (1.419–1.538 Å) with retention of aromaticity. In contrast, 5-Lil·PMDTA and laterally lithiated N-trimethylsilyl o
Valence isomerization of cyclohepta-1,3,5-triene and its heteroelement analogues
Beilstein J. Org. Chem. 2011, 7, 1713–1721, doi:10.3762/bjoc.7.201
- -1,3,5-triene into the corresponding bicyclo[4.1.0]hepta-2,4-dienes is reviewed to show the impact of the heteroatom on the stability of both valence isomers. The focus is on the parent systems and their synthetic applications. Keywords: aromaticity; cycloheptatriene; heteroatom; valence isomerization
Chiral recognition of ephedrine: Hydrophilic polymers bearing β-cyclodextrin moieties as chiral sensitive host molecules
Beilstein J. Org. Chem. 2011, 7, 1516–1519, doi:10.3762/bjoc.7.177
- aromaticity and is pharmaceutically relevant (Scheme 1). Recently we described the monomer synthesis of mono-(6-azido-6-desoxy)-β-cyclodextrin with propargylmethacrylate and the copolymerization with N-isopropylacrylamide (NIPAAM) [20]. The properties of the polymer 1 were characterized further by use of size
Solvent- and ligand-induced switch of selectivity in gold(I)-catalyzed tandem reactions of 3-propargylindoles
Beilstein J. Org. Chem. 2011, 7, 786–793, doi:10.3762/bjoc.7.89
- present at either of these positions, they undergo further cyclizations to afford 3-(inden-2-yl)indoles 3 or 4 (Scheme 1). An analysis of the aromaticity of the transition state structures for these cyclizations by DFT calculations revealed that these electrocyclic ring closures could be considered as
Synthetic applications of gold-catalyzed ring expansions
Beilstein J. Org. Chem. 2011, 7, 767–780, doi:10.3762/bjoc.7.87
- activation of the cyclopropene, cation 55 is formed. C–C bond cleavage of the cyclopropyl ring followed by a Friedel–Crafts reaction affords, after recovery of aromaticity, the observed products [47]. 4 Ring expansions involving annulation reactions Diels–Alder, [1,3]-dipolar-, [2 + 2]- and [4 + 3
The arene–alkene photocycloaddition
Beilstein J. Org. Chem. 2011, 7, 525–542, doi:10.3762/bjoc.7.61
- alkenes with arenes. The last part includes a related class of cycloadditions with arenes, where the aromaticity on the final compounds is restored. In this review, we will call this class “non-classical” photocycloadditions. Review Classical photocycloaddition of alkenes to arenes While the meta
Synthesis of 5-(2-methoxy-1-naphthyl)- and 5-[2-(methoxymethyl)-1-naphthyl]-11H-benzo[b]fluorene as 2,2'-disubstituted 1,1'-binaphthyls via benzannulated enyne–allenes
Beilstein J. Org. Chem. 2011, 7, 496–502, doi:10.3762/bjoc.7.58
- aromaticity to furnish 13a as proposed previously [5]. An intramolecular [2 + 2] cycloaddition reaction of 10a or a direct radical–radical coupling of 11a could account for the formation of 14a [5]. From 9b, 5-[2-(methoxymethyl)phenyl]-11H-benzo[b]fluorene 13b and the [2 + 2] cycloaddition adduct 14b were
β-Hydroxy carbocation intermediates in solvolyses of di- and tetra-hydronaphthalene substrates
Beilstein J. Org. Chem. 2010, 6, 1035–1042, doi:10.3762/bjoc.6.118
- –H hyperconjugation is particularly pronounced for a β-hydroxynaphthalenium ion intermediate because the stability of its no-bond resonance structure reflects the presence of an aromatic naphthol structure. Keywords: aromaticity; β-hydroxycarbocations; hyperconjugation; solvolysis; Introduction Cis
- intermediate (2) [3]. This contrasts with reactions of cis- and trans-dihydrodiols of non-aromatic double bonds for which only a small advantage for the cis-diol is observed. Indeed, the cis/trans rate ratio decreases regularly as the aromaticity of the double bond decreases, as shown for the dihydrodiols of
- solvolysis ot 4-trans. Measurements for benzene and phenanthrene dihydrodiols confirm that, whereas the ratio of cis-rate constants to those of the corresponding alcohols, which lack a β-hydroxy group, remains roughly constant, those for the trans-dihydrodiols increase sharply as the aromaticity of the
Structure and reactivity in neutral organic electron donors derived from 4-dimethylaminopyridine
Beilstein J. Org. Chem. 2010, 6, No. 73, doi:10.3762/bjoc.6.73
- ][7][8][9][10][11][12], but is not strong enough to react with alkyl and aryl halides. The driving force for its oxidation is the attainment of some degree of aromaticity in the formation of its radical cation salt 2 on the loss of one electron, and full aromaticity in its dication salt 3 on loss of
Ring-alkyl connecting group effect on mesogenic properties of p-carborane derivatives and their hydrocarbon analogues
Beilstein J. Org. Chem. 2009, 5, No. 83, doi:10.3762/bjoc.5.83
- and are characterized by 3-dimensional σ-aromaticity and high-order symmetry axis [23]. Therefore, it is of interest to understand how the electronic properties of the two clusters and their unusual molecular symmetry and size affect bulk properties of mesogens. Through extensive comparison of
Inversion symmetry and local vs. dispersive interactions in the nucleation of hydrogen bonded cyclic n-mer and tape of imidazolecarboxamidines
Beilstein J. Org. Chem. 2008, 4, No. 23, doi:10.3762/bjoc.4.23
- denser than aliphatic organics [37]. This is likely due to the fact that bonds are shorter for sp2/sp2 atoms than for sp3/sp3 atoms. The effect of aromaticity on density is likely enhanced because these double aromatic substituents in these small structures accounted for much of the molecular mass. In
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