联苯基团引起的激发三重态重排活性增长

双发色团分子光化学研究兴趣与日俱增。我们在以前报道一个有趣的现象:基态发色团间的分子轨道交叠左右光反应机理。3-甲基-3-联苯基-1-丁烯(1),是有特殊意义的分子。与激发能高达(143 kcal/mol)的孤立双键相比,联苯基的激发能特别低(69 kcal/mool)。如此大的激发能差使乙烯基与联苯 p电子间的交叠通道更加畅通,基态1的稳定构象是 endo 型,1的光化学行为将不同于无环双π甲烷分子。1000 W 高压汞灯照射1的正已烷溶液,     

A novel photoinduced ring opening and isomerization of adamantane-2-spiro isoxazolines using Mo(CO)6

The Mo(CO)₆-mediated photoinduced ring-opening reactions of adamantane isoxazolines involve novel rearrangement that provide enaminoketones as major products and β-hydroxy ketones as minor ones; in contrast, only β-hydroxy ketones and α,β-unsaturated ketones were obtained under thermal condition.     

Photoreactions of a polyamic acid containing 2,2-dinitrodiphenylmethane segments at symmetrical positions in the main chain

A polyamic acid containing 2,2^′-dinitrodiphenylmethane segments in the main chain was synthesized from 4,4^′-diamino-2,2^′-dinitrodiphenylmethane and pyrromellitic dianhydride. Irradiation of the polyamic acid was done in solution (in a protic solvent, isopropanol, in isopropanol in the presence of a triplet exciter, benzophenone and in acidified isopropanol) and as thin film. The irradiations were done in an immersion type photoreactor using a 125 W high-pressure mercury vapour lamp. The average molecular weights of the polymers were determined by gel permeation chromatography. The polydispersity index of the polyamic acid and the photoproduct showed the absence of photodegradation. The photoproducts were identified by comparing the spectra of polymer photoproducts with that of low molecular weight 2,2^′-dinitrodiphenylmethane derivatives under identical conditions. A possible mechanism for the phototransformations is suggested. Evaluation of photoresist behaviour of the polyamic acid was also done.     

Construction of polyaromatics via photocyclization of 2-(fur-3-yl)ethenylarenes,using a 3-furyl group as an isopropenyl equivalent synthon

The construction of different types of substituted arenes was demonstrated through the photocyclization of 2-(fur-3-yl)ethenylarenes using a 3-furyl group as an isopropenyl equivalent synthon in the photocyclization reaction. The furan portion of the photocyclization intermediate could be fragmented via a base-induced elimination reaction to yield a series of substituted polyaromatics, including naphthalene, benzofuran, benzothiophene, phenanthrene, phenalene, acenaphthene, and triphenylene. Using different reagents, this method made it possible to introduce methyl or 2-hydroxyethyl groups as substituents at specific positions in these arenes.     

Photorearrangement of o‐Methoxystilbenoids in Acid Media

Photorearrangements of o‐methoxystilbenoils ( 1a‐1c ) in acid media have been investigated. Irradiation of o‐methoxystilbene ( 1c ), for example, could lead to three major rearrangement products: 2,3,4‐trihydrophenanthren‐1‐ones ( 2c ), trans‐1‐arylbut‐2‐en‐1‐ones ( 3c ), and 1‐hydroxy‐9,10‐dihydrophenanthrenes ( 7 ). Further irradiation of trans‐1‐arylbut‐2‐en‐1‐ones ( 3 ) could afford three more products ( 4 , 5 and 6 ). The key step for this photorearrangement is acid‐catalyzed formal [1,9] hydrogen shift. The products of the eliminative and oxidative photoreaction were also obtained; the formation of the oxidative product is due to the fact that the unfavorable methoxy group in the intermediate DHP‐3 retards the rate of acid‐catalyzed formal [1,9] hydrogen shift.     

Photo-Fries rearrangement of 1-pyrenyl esters

Photo-Fries rearrangement reactions of 1-pyrenyl esters were investigated. Photoreaction of 1-pyrenyl benzoate in benzene generates 1-hydroxy-2-pyrenyl phenyl ketone along with 1-pyrenol. The exceptionally down field ¹H NMR chemical shift of OH proton in the photoproduct indicates the existence of intramolecular hydrogen bonding. Photorearrangements of analogs that have electron-withdrawing or electron-releasing group on the phenyl ring, and related heteroaromatic carboxylates also take place to form the corresponding ketones. However, photoreactions of 1-pyrenyl aliphatic carboxylate esters do not occur. The results of spectroscopic and theoretical studies suggest the mechanistic pathway for this process is initiated by homolytic CO bond cleavage in an aroyl group localized ¹(π?→?π¹) excited state of the 1-pyrenyl esters. The radical pair generated in this fashion then undergoes in-solvent-cage coupling to yield the 1-hydroxy-2-pyrenyl aryl ketone selectively.     

Photochemistry of cyclopropanes, methylenecyclopropanes, and vinylidenecyclopropanes

This review deals with the recent advances in the photochemistry of cyclopropanes, methylenecyclopropanes, and vinylidenecyclopropanes. cis–trans Photoisomerization of 1,2-diarycyclopropanes via excited singlet and triplet states and radical cations, photochemical polar addition to arylcyclopropanes, and photooxygenation of arylcyclopropanes and methylenecyclopropanes giving cyclic peroxides are described. The new photochemistry of vinylidenecyclopropanes including cis–trans photoisomerization, (3+2) photocycloadditions, and photorearrangements is also discussed.     

Photochemical behaviour of 5-perfluoroalkenyl uracils

Phototransformations of derivatives of 5-fluoroalkenyl uracils depend strongly on the fluorinated substituents. 1,3-Dimethyl-5-trifluorovinyluracil when irradiated in water with UV light (λ>300 nm) gives 1,3-dimethyl-(5,6-dihydrourac-6-yl)-difluoroacetic acid as the only product, while the analogous 1,3-dimethyl-5-(E-pentafluoropropenyl)uracil isomerizes to its Z isomer. It is suggested that the first transformation is thermodynamically controlled while the second one is kinetically controlled, the difference being due to torquoselectivity.     

Photorearrangements in spiro-conjoined cyclohexa-2,5-dien-1-one

The unexpected formation of cyclohexa-2,5-dien-1-one (6) spiro-conjoined with a dihydrobenzofuran framework, and the photochemical behavior of this compound in solution as well as in the solid state are described. The photoreaction of 6 in solution affords two rearranged products, one (7) accompanied by the enlargement of the oxygen heterocyclic ring and the other (8) accompanied by cyclopentadienone fragmentation. In the solid state, the former is the sole photoproduct of both solvated and desolvated crystals. The desolvated crystals were obtained as polycrystalline solids by thermal release of solvent molecules, and its structure was elucidated by ab initio determination from X-ray powder diffraction data followed by the Rietveld refinement.