104394-23-2Relevant academic research and scientific papers
Novel radical cation reactions of bichromophoric systems. Transannular aryl migrations; Mechanistic and exploratory organic photochemistry
Zimmerman, Howard E.,Hoffacker, Kurt D.
, p. 6526 - 6534 (2007/10/03)
Eight aryl-substituted 1,4-pentadienes were subjected to photochemically induced electron transfer using dicyanonaphthalene and dicyanoanthracene. The radical-cations produced underwent a regioselective cyclization, wherein one electron-deficient aryl group of one diarylvinyl moiety bonds to the β-carbon of the second diarylvinyl group. A pattern of regioselectivity and reactivity was encountered. As cyclization proceeds, the odd-electron density becomes localized in the benzhydryl side chain while the positive charge becomes localized in the second portion of the molecule. Substitution in one diarylvinyl branch designed to delocalize odd-electron density but destabilize electron deficiency led to higher reactivity than the unsubstituted parent 1,1,5,5-tetraphenyl-3,3-dimethyl-1,4-pentadiene. The benzhydryldihydronaphthalene photoproducts themselves proved photochemically reactive. On sensitization, the benzhydryldihydronaphthalene reacted with a transannular 1,5-migration of one aryl group of the benzhydryl moiety. Where the two benzhydryl aryl groups were different, the cyanophenyl group migrated in preference to phenyl, and both diastereomers led to the same product stereoisomer. Ab initio and semiempirical computations were in accord with the radical cation and triplet regioselectivity.
A Photochemical Long-Range Pinacol Rearrangement. Mechanistic and Exploratory Organic Photochemistry
Zimmerman, Howard E.,Nuss, John M.
, p. 4604 - 4617 (2007/10/02)
In a previous study we uncovered a rearrangement in which a phenyl group migrated 1,4 from a benzhydryl carbon to an excited diphenylvinyl chromophore.The present study aimed at generalizing this bizarre rearrangement and also in ascertaining if an aryl migration would occur from a carbinol carbon.Indeed, the irradiation of 1,1,5,5-tetraphenyl-3,3-dimethyl-4-penten-1-ol led smoothly to 1,4,5,5-tetraphenyl-3,3-dimethyl-1-pentanone.The overall mechanism involves a transannular phenyl migration in a process reminiscent of a pinacol rearrangement.At conversions above 20percent and at wavelengths other than 280 nm, a secondary process was observed wherein a type II fragmentation afforded 1,1,2-triphenyl-3-methyl-2-butene and acetophenone.The initial rearrangement and primary process was shown to proceed via the excited singlet of the tetraphenyldimethylpentenol while the corresponding triplet proved unreactive.An alternate mechanism leading directly from the tetraphenyldimethylpentenol to acetophenone and the triphenylbutene was considered as possibly accounting for part of the overall fragmentation reaction.However, this was precluded by a kinetic study using our dynamic isotope dilution method.An analogous transannular migration was observed for the corresponding methyl ether, which rearranged to afford 1-methoxy-1,4,5,5-tetraphenyl-3,3-dimethyl-1-pentene.Here there was no complicating type II secondary process.Another aspect studied was the facility of migration of different aryl groups.Thus it was observed that when one phenyl group of the methyl ether was replaced by p-cyanophenyl, only the cyanophenyl group migrated.With one phenyl group replaced by anisyl, anisyl migrated with a 2:1 preference relative to phenyl.As in the case of the tetraphenyldimethylpentenol, the singlet excited state was the reactive species.Quantum yields were determined.The tetraphenyldimethylpentenol had an effciency of 0.0026 which was ca. 2.5 times that of our previously studied rearrangement lacking the hydroxyl group.The corresponding methyl ether had a quantum yield of 0.0041.The cyanophenyl migration efficiency was 0.0038, and the total quantum yield of the anisyl analogue was 0.0032.Also, singlet excited state reaction rates were determined by single photon counting.Finally, in the case of the tetraphenyldimethylpentenol rearrangement, deuteration studies showed that the initially formed diradical, resulting from completion of the phenyl migration, leads to product both by hydrogen transfer from the hydroxyl oxygen as well as from the adjacent carbon.
