256-81-5Relevant academic research and scientific papers
Laser Flash Photolysis Studies of Dibenzosuberenyl Cations and Radical Cations
Johnston, L. J.,Lobaugh, J.,Wintgens, V.
, p. 7370 - 7374 (1989)
A variety of dibenzosuberenyl systems have been investigated by laser flash photolysis.Excitation of the parent alcohol, 5-dibenzosuberenol, in trifluoroethanol yields the corresponding carbocation via heterolysis of the C-OH bond.The carbocation shows a long-lived (>100 μs) absorption at 525 nm with a second band at 390 nm, is readily quenched by nucleophiles (kq(azide) = 1.1 * 1E9 M-1 s-1), and fluoresces with a lifetime of 35 ns.In other solvents, the transient phenomena are dominated by the formation of the radical cation via a two-photon process.Both dibenzosuberene and 5-phenyl-5-dibenzosuberenol also yield radical cations in a variety of polar solvents.The radical cations show absorption spectra with maxima at 470 nm and a broad band in the 700-nm region, have lifetimes in oxygenated solutions of > 1.5 μs, and react with a variety of nucleophiles.Their identity has been confirmed on the basis of their independent generation with the electron-transfer sensitizers chloranil and 1,4-dicyanonaphthalene and by reaction with 1,2,4-trimethoxybenzene.
Synthesis and characterization of ion pairs between alkaline metal ions and anionic anti-aromatic and aromatic hydrocarbons with π-Conjugated central seven- And eight-membered rings
Bloch, Jan,Dey, Subal,Gianetti, Thomas L.,Grützmacher, Hansj?rg,Kradolfer, Stefan,Mougel, Victor,Ostendorf, Detlev
, (2020/10/27)
The synthesis, isolation and full characterization of ion pairs between alkaline metal ions (Li+, Na+, K+) and mono-anions and dianions obtained from 5H-dibenzo[a,d]cycloheptenyl (C15H11 = trop) is reported. According to Nuclear Magnetic Resonance (NMR) spectroscopy, single crystal X-ray analysis and Density Functional Theory (DFT) calculations, the trop- and trop2?? anions show anti-aromatic properties which are dependent on the counter cation M+ and solvent molecules serving as co-ligands. For comparison, the disodium and dipotassium salt of the dianion of dibenzo[a,e]cyclooctatetraene (C16H12 = dbcot) were prepared, which show classical aromatic character. A d8-Rh(I) complex of trop? was prepared and the structure shows a distortion of the C15H11 ligand into a conjugated 10π -benzo pentadienide unit—to which the Rh(I) center is coordinated—and an aromatic 6π electron benzo group which is non-coordinated. Electron transfer reactions between neutral and anionic trop and dbcot species show that the anti-aromatic compounds obtained from trop are significantly stronger reductants.
Iodine-catalyzed disproportionation of aryl-substituted ethers under solvent-free reaction conditions
Jereb, Marjan,Vrazic, Dejan
, p. 1978 - 1999 (2013/05/22)
Iodine was demonstrated to be an efficient catalyst for disproportionation of aryl-substituted ethers under solvent-free reaction conditions. Variously substituted 1,1,1′,1′-tetraaryldimethyl ethers were transformed into the corresponding diarylketone and diarylmethane derivatives. I 2-catalyzed transformation of 4-methoxyphenyl substituted ethers yielded mono- and dialkylated Friedel-Crafts products as well. Treatment of trityl alkyl and trityl benzyl ethers with a catalytic amount of iodine produced triphenylmethane and the corresponding aldehydes and ketones. The electron-donating substituents facilitated the reaction, while the electron-withdrawing groups retarded it; the difference in reactivity is not very high. Such an observation may be in favour of hydride transfer, predominantly from the less electron rich side of the ether with more stable carbocation formation. With the isotopic studies it was established that a substantial portion of the C-H bond scission took place in the rate-determining step, while the carbonyl oxygen atom originated from the starting ether, and not from the air. The transformation took place under air and under argon, and HI was not a functioning catalyst.
Flow-vacuum pyrolysis of dibenzocycloheptane derivatives on zeolites catalysts. IV
Istrati, Daniela,Parvulescu, Luminitza,Popescu, Angela,Mihaiescu, Dan,Badea, Florin
scheme or table, p. 711 - 714 (2011/10/02)
The pyrolysis of 10,11-dihydro-5H-dibenzo[a,d]cicloheptadien-5-ol (4) and of 5H-dibenzo[a,d]cycloheptatrien-5-ol (5) in flowvacuum conditions (advanced vacuum, inert atmosphere) on zeolites at 300°C is presented. The reaction products were identified by GC/MS using authentic samples and a reaction mechanisms involving cationic species as intermediates were proposed. A comparison with the pyrolysis of the same compounds performed in FVP conditions on quartz is presented.
Flow-vacuum pyrolysis of polycyclic compounds. 151 pyrolysis of three RELATED dibenzocycloalkanols
Banciu, Mircea D.,Popescu, Angela,Parvulescu, Lumini?a,Ciuculescu, Crinu,Drǎghici, Constantin,Banciu, Anca,Mihǎiescu, Dan
, p. 239 - 248 (2007/10/03)
The flow-vacuum pyrolyses of cis-9,10-bis(hydroxymethyl)-9,10-dihydroanthracene (4); 6H-5,7-dihydrodibenzo[a,c]cyclohepten-6-ol (5) and 5H-dibenzo[a,d]cyclohepten-5-ol (6) were studied at 1.33 mbar in argon atmosphere over a large temperature interval. The main pyrolysis product of 4-cis was anthracene (13), accompanied by traces of 9-methylanthracene (15) and 9-anthraldehyde (14). The main pyrolysis products of 5 were: 9-methylphenanthrene (17) and 5H-dibenzo[a,c]cycloheptene (16), whereas phenanthrene (19) and fluorene (18) were minor products. From the flow-vacuum pyrolysis of 6 the corresponding ketone (dibenzosuberenone 12) and 5H-dibenzo[a,d]cycloheptene (20) were the major products and anthracene and 9-methylanthracene the minor ones. The thermal behavior of 4-cis, 5 and 6 was rationalized on the basis of mechanisms including radical and concerted steps. Some parts of the here proposed mechanisms were confirmed by our previous works describing the conversions of authentic 16 and 20 to the same end-products: 17 + 19, respectively 13 + 15. A comparison with the thermal behaviour of other related dibenzocycloalkanols is also made.
The first efficient synthesis and optical resolution of monosubstituted cyclotribenzylenes
Schmuck, Carsten,Wienand, Wolfgang
, p. 655 - 663 (2007/10/03)
A new and high yielding synthetic route to monosubstituted cyclotribenzylenes 6 via the cyclocondensation of benzene with a suitably monosubstituted diol 20, obtained from ozonolysis of the corresponding dibenzosuberene precursor 19, was developed for the first time! The dibenzosuberene itself could be readily prepared in large quantities from inexpensive starting materials in five steps. Using this synthetic approach, a mono bromosubstituted cyclotribenzylene 12a was synthesized on large scale. Another four monosubstituted cyclotribenzylenes 21-24 were also prepared either via bromine/lithium exchange followed by subsequent quenching with external electrophiles or a copper mediated reaction with cyanide. These molecules adopt a rigid crown conformation as shown by X-ray analysis and temperature dependent NMR studies. The barrier to inversion is quite high, requiring temperatures well above 120°C before inversion takes place. Futhermore, such monosubstituted cyclotribenzylenes are planar chiral and after optical resolution, using HPLC, we were able to obtain the first planar chiral Cl-symmetric cyclotribenzylenes in form of the optically pure enantiomers of 12a, the CD spectra of which are exact mirror images over the entire spectral range.
Hypophosphorous acid-iodine: A novel reducing system. Part 1: Reduction of diaryl ketones to diaryl methylene derivatives
Hicks,Han,Fry
, p. 7817 - 7820 (2007/10/03)
A mixture of hypophosphorous acid (H3PO2) and iodine in hot acetic acid reduces diaryl ketones quickly and aryl alkyl ketones slowly to the corresponding methylene derivatives. The active reducing agent is hydrogen iodide, generated by reaction between iodine and hypophosphorous acid. (C) 2000 Elsevier Science Ltd.
Electrophilic Reactions of the Dibenzotropylium Ion
Henninger, Joachim,Mayr, Herbert,Patz, Matthias,Stanescu, Michaela Dina
, p. 2005 - 2010 (2007/10/03)
The kinetics of the hydride transfer reactions of the dibenzotropylium ion (2) with dimethylphenylsilane (5) and triphenylsilane (6) were used to determine its electrophilicity parameter E = -0.71.The ? nucleophiles 7-9 react 10-40 times faster with 2 than expected from the linear free energy relationship (1), probably due to the formation of a ?-stabilized carbocation (e.g. 15).A detailed investigation of the reaction of 2 with isobutene (4) shows that the linear addition product 13a and the cyclization products are not formed via a common intermediate. - Keywords: Carbenium ions; Kinetics; Electrophilicity
Photodecarboxylation of diarylacetic acids in aqueous solution: Enhanced photogeneration of cyclically conjugated eight π electron carbanions
Krogh, Erik,Wan, Peter
, p. 705 - 712 (2007/10/02)
The photodecarboxylation of a series of diarylacetic acids 1-6 has been studied in aqueous solution. The mechanism of these photodecarboxylations is shown to involve C-C bond heterolysis from the singlet excited state, giving rise to carbanion intermediates. Quantum yields for photodecarboxylation (Φd) are reported at several pH's. Fluorescence quantum yields and lifetimes are reported as a function of pH, and their behavior is consistent with reaction via the carboxylate ions. Rate constants of photodecarboxylation (kdc) are estimated and show a marked dependence on the number of π electrons in the internal cyclic array (ICA). The most reactive compound was suberene-5-carboxylic acid (1) (Φd = 0.60 ± 0.05; kdc ≈ = 6 × 109 s-1), which gives a carbanion intermediate of eight π (4n) electrons in the ICA. The least reactive system was fluorene-9-carboxylic acid (4) (πd = 0.042 ± 0.004; kdc = 8.8 × 106 s-1), which on decarboxylation gives rise to a carbanion with an ICA of six π (4n + 2) electrons. The observed reactivity trend in the excited state is the reverse of that observed in the ground state and appears to demonstrate further the utility of the "4n rule" for predicting the relative reactivity of photochemical reactions giving rise to cyclically conjugated, charged intermediates. The possible theoretical significance of these observations is discussed.
Excited-State Carbon Acids. Facile Benzylic C-H Bond Heterolysis of Suberene on Photolysis in Aqueous Solution: A Photogenerated Cyclically Conjugated Eight ? Electron Carbanion
Budac, David,Wan, Peter
, p. 887 - 894 (2007/10/02)
The possibility of excited-state carbon acid behavior of the dibenzylic protons of several dibenzannelated systems related to suberene (1) has been investigated in aqueous solution and in several organic solvents.It was found that only suberene (1) displayed observable excited-state carbon acid behavior.Thus photolysis of 1 in D2O-CH3CN solutions resulted in facile exchange of the benzylic protons with deuterium from D2O.Extended photolysis resulted in incorporation of two deuteriums at the benzylic position.Quantum yields for initial deuterium incorporation are in the range 0.02-0.03 for 1 in D2O-CH3CN solutions.Deuterium exchange from the benzylic position with solvent protons was also observed on photolysis of 5,5-dideuterio-5H-dibenzocycloheptene (2), where each deuterium atom was exchanged with solvent H2O in a sequential manner.Fluorescence quenching by water (in CH3CN solution) of the exchanging suberene systems (1 and 2) gave linear Stern-Volmer plots, with kq = (1.68 +/- 0.08) * 1E8 M-1 s-1 for 1 and (0.61 +/- 0.06) * 1E8 M-1 s-1 for 2, which corresponds to an isotope effect for quenching by water, (kH/kD)q = 2.8 +/- 0.4.Fluorescence titration of 1 and 11 as a function of medium acidity gave an estimate of pK(S1) ca. -1 for these carbon acids.This compares to their estimated pK(S0) ca. 31-38.
