1217-12-5Relevant academic research and scientific papers
ISOMERIZATION OF DEWAR BENZENES INVOLVING ELECTRON DONOR-ACCEPTOR EXCIPLEXES
Jones II, Guilford,Chiang, Sheau-Hwa
, p. 3397 - 3404 (1981)
Valence photoisomerization of hexamethyl (Dewar benzene) (HMDB) is sensitized by aromatic singlet photosensitizers 1,4-dicyanobenzene, 1-cyanonaphthalene, 9-cyanoanthracene, and 9,10-dicyanoanthracene with a limiting quantum efficiency of 1.0 in cyclohexane solvent.Quenching of the fluorescence of the aromatic sensitizers leads to exciplex emission which is identical to that obtained by quenching with the isomer, hexamethylbenzene (HMB).The emission is identified as HMB exciplex emission on the basis of relative lifetime and dual quenching experiments.The relative yield of HMDB-derived ("adiabatic") emission is 20-50percent depending on the excitation energy of the HMB exciplex product.Neither biacetyl singlet or triplet nor 1-cyanonaphthalene triplet photosensitization is successful in bringing about isomerization of HMDB.Dimethyl 1,4,5,6-tetramethylbicyclohexa-2,5-diene-2,3-dicarboxylate undergoes valence isomerization on quenching electron donor fluorophores, with a quantum efficiency of 0.2.The aromatic valence isomer is not produced in an excited state in this case.Factors which govern the efficiency of adiabatic and diabatic isomerization of the Dewar benzenes are discussed, including sensitizer redox properties, configuration, and multiplicity, the excitation energy and binding characteristics of exciplexes, and the Dewar benzene substituent pattern.
Dimethyl octamethyltricyclo[4.2.2.02,5] deca-3,759-triene-7,8-dicarboxylate (Cookson's diester) revisited: Cope rearrangement and epoxidation site selectivity
Warrener, Ronald N.,Elsey, Gordon M.,Pitt, Ian G.,Tiekink, Edward R.T.,Russell, Richard A.
, p. 1075 - 1078 (1994)
Dimethyl octamethyltricyclo[4.2.2.02,5]deca-3,7,9-triene-7,8-dicarboxylate (Cookson's diester) (8) is rearranged thermally via a double Cope reaction to its ring-degenerate isomer (14). The structure of diester (8) (indirectly) and the rearrangement product (14) (directly) are placed on an unequivocal base by X-Ray structure analysis. AMI semi-empirical calculations support the preferential formation of (8) from the reaction of DMAD with transient intermediate diene (7). Epoxidation studies (mCPBA) have been conducted and firm site selectivities determined. A correction is made to an earlier report on the epoxidation selectivity of (18).
Dewar benzene as a protecting group? demonstration of photolithographic crystallization
Marsella, Michael J.,Meyer, Mathew M.,Tham, Fook S.
, p. 3847 - 3849 (2001)
The concept of Dewar benzene as a supramolecular protecting group for solid-state aryl-aryl interactions is reported. Photoisomerization of 1,4,5,6-tetramethyl-bicyclo[2.2.0]hexa-2,5-diene-2,3-dicarboxylic acid dimethyl ester (1) to the corresponding benzene isomer proceeds with rapid crystal formation. Herein this property is applied to the photolithographic patterning of crystal domains on a surface.
Quantum amplified isomerization in polymers based on triplet chain reactions
Ferrar, Lorraine,Mis, Mark,Dinnocenzo, Joseph P.,Farid, Samir,Merkel, Paul B.,Robello, Douglas R.
, p. 5683 - 5692 (2008/12/22)
(Graph Presented) Photoinitiated triplet quantum amplified isomerizations (QAI) of substituted Dewar benzene derivatives in polymeric media are reported. The quantum efficiencies and the ultimate extents of reactant-to-product conversions increase significantly with the incorporation of appropriate co-sensitizers; compounds whose triplet energies are similar to or lower than that of the sensitizer and close to that of the reactant. These co-sensitizers serve to promote chain-propagating energy transfer processes and thereby increase the action sphere of photosensitization. Isomerization quantum yields increase, as predicted, with increasing concentrations of the reactants and the co-sensitizers. Chain amplifications as large as ～16 and extents of conversion that approach 100% have been achieved. Mechanistic schemes are proposed to account for the dynamics of the inherent energy transfer processes and provide a predictively useful model for the design of a new class of photoresponsive polymers based on changes in the refractive index of the materials.
Revisiting Cyclobutadienemetal Complexes: High-Content Dewar Benzene Polymers and a One-Pot Synthesis of Permethylated Ladderanes
Marsella, Michael J.,Estassi, Samia,Wang, Li-Sheng,Yoon, Kunsang
, p. 192 - 194 (2007/10/03)
High-content Dewar benzene polymers and sterically congested [n] -ladderanes have been synthesized from [4πs+2πs] cyclobutadienemetal complex cycloaddition chemistry. In the former case, tetramethylcyclobutadiene-AlCl3 is reacted with an acetylene-containing precursor polymer to yield > 95% Dewar benzene incorporation. In the latter case, [n]-ladderanes containing up to thirteen rings are prepared via a one-pot procedure from 2-butyne.
Cycloaddition of thiophene S-oxides to allenes, alkynes and to benzyne
Thiemann, Thies,Fujii, Hideki,Ohira, Daisuke,Arima, Kazuya,Li, Yuanqiang,Mataka, Shuntaro
, p. 1377 - 1384 (2007/10/03)
Thiophenes have been treated with alkynes in the presence of m-chloroperoxybenzoic acid to give substituted arenes as cycloadducts. Alternatively, thiophene S-oxides have been prepared by oxidation from thiophenes and have been subjected to cycloaddition with alkynes in a subsequent step. The outcome of the reaction is dependent on the steric demand of the thiophene S-oxide. Some thiophene S-oxides can be reacted at temperatures as high as 140°C without decomposition. Thiophenes as deoxygenated products are the main by-products. Reactions of thiophene S-oxides with allenes give in part thiabicyclo[2.2.1]heptene S-oxides of type 12a and 13 along with aromatized products. Thiophene S-oxides also cycloadd to benzyne.
Valence Isomerizations, 18. - Valence Isomerizations of Persubstituted (CH)10 Systems
Maier, Guenther,Wiegand, Norbert Hermann,Baum, Stefan,Wuellner, Reinhold
, p. 781 - 794 (2007/10/02)
Within the synthesis of persubstituted dihydronaphthalenes, altogether nineteen octamethylbis(methoxycarbonyl)-substituted valence isomers have been isolated, and their structures and mutual relationships clarified.Compared to the unsubstituted parent compounds, there are remarkable differences.The same is true for seven valence-isomeric forms of permethylated (CH)10 hydrocarbons which correspond to diesters and are also presented in this article. - Keywords: Persubstituted (CH)10 systems / Photochemical and thermal isomerizations / Steric crowding / Valence isomerizations
AROMATIC RING SYNTHESIS BY N-AMINOPYRROLE DIELS-ALDER REACTION. CHARACTERIZATION OF THE HETEROATOM FRAGMENT
Schultz, Arthur G.,Shen, Ming,Ravichandran, Ramanathan
, p. 1767 - 1770 (2007/10/02)
Aminonitrenes are produced on reaction of N-aminopyrroles with dimethyl acetylenedicarboxylate; a new reaction of dialkyl aminonitrenes is described.
