55042-91-6Relevant academic research and scientific papers
An Intermediate in the Aryl Halide Photocyclization Process detected by Flash Photolysis
Grimshaw, James,Trocha-Grimshaw, Jadwiga
, p. 744 - 745 (1984)
A transient intermediate which decays in a first-order process with k = 12.6 s-1 in the photochemical cyclization of 5-(2-chlorophenyl)-1,3-diphenylpyrazole has been observed; because of the relatively long lifetime this is probably a cyclohexadienyl radical.
Example of Predissociation between Separate Chromophores in 5-(2-Halogenoaryl)-1,3-diphenyl-Δ2-pyrazolines
Grimshaw, James,Silva, A. Prasanna de
, p. 1236 - 1237 (1980)
Photoexcited 5-(2-iodophenyl)-1,3-diphenyl-Δ2-pyrazoline undergoes carbon-iodine bond homolysis via energy transfer from the 1,3-diphenylpyrazoline moiety to a dissociative state, whereas photoexcited 5-(5-bromo-3-methoxycarbonylphenyl)-1,3-diphenyl-Δ2-pyrazoline undergoes electron transfer.
Synthesis of 7-Substituted Indoles as Potential Ligand Precursors
Black, David St.C.,Deacon, Glen B.,Edwards, Gavin L.
, p. 1771 - 1781 (2007/10/02)
Some 7-(pyridin-2'-yl)- and 7-(pyrazol-1'-yl)-indole-2-carboxylic esters (14)-(16) and the related acids (17) and (18) have been synthesized through the Fischer indole cyclizations of the ethyl pyruvate hydrazones (9)-(12), which were in turn derived from
Photocyclization of Aryl Halides. Part 4. 5-(2-Halogenophenyl)-1,3-diphenyl-Δ2-pyrazolines. Predissociation and Electron Transfer between Intramolecular but Separate Chromophores
Grimshaw, James,Silva, A. Prasanna de,
, p. 1679 - 1686 (2007/10/02)
Photoreaction of 5-(2-iodophenyl)-1,3-diphenyl-Δ2-pyrazoline proceeds by simple bond homolysis from the S1deg state to give 1,3,5-triphenylpyrazoline and 2-phenylpyrazolophenanthridine in a ratio which depends on the hydrogen atom donor ability of the hydrocarbon solvent.The quantum yield for decomposition of the iodo-compound depends on the viscosity of the hydrocarbon solvent and on the temperature.The corresponding chloro- and bromo-compounds as well as the 3-iodo- and 4-iodo-phenyl compounds are photostable.Consideration of these facts and the complementary fluorescence data suggest a mechanism of interchromophoric predissociation to an n?* state.However, examples are given where there is a smaller electron donor-acceptor energy gap between the two chromophores so that photoreaction occurs by an electron transfer pathway.
Photocyclization of aryl halides. Part I. 5-(2-Halogenophenyl)-1,3-diphenylpyrazoles; homolytic fission assisted by radical complexation
Grimshaw, James,Silva, A. Prasanna de
, p. 1880 - 1888 (2007/10/02)
The photocyclization of 5-(2-halogenophenyl)-1,3-diphenylpyrazoles proceeds efficiently with the exclusion of solvent participation hydrogen abstraction reactions.In a given solvent, the quantum yields of cyclization (Φ) of Cl, Br, and I compounds show no correlation with carbon-halogen bond dissociation energies.In a series of solvents, Φ varies smoothly with solvent viscosity and is independent of solvent polarity.The Φ values are independent of triplet quenchers, air, intensity and wavelength of radiation, and reactant concentration.Photocyclization can be triplet sensitized at up to 80percent of the direct reaction rate and the reactant triplet energies are about 65 kcal mol-1 while DC-Br is 81 and DC-Cl is 95 kcal mol-1.A mechanism of homolytic fission assisted by radical complexation is proposed to accomodate the results.Photocyclization of the H- and MeO-substituted analogues proceeds inefficiently and with Φ values dependent on solvent polarity.An electrocyclic mechanism is followed in these cases.The assisted homolysis model explains several anomalies in the field of aryl halide photochemistry.
