Natasa Zupancic

1,2-, 1,3- and 1,4-Photocycloaddition modes on the naphthalene ring

The photochemical reaction of octafluoronaphthalene and indene results in all three cycloaddition modes, i.e., 1,2-, 1,3- and 1,4-cycloaddition take place.

Photosubstitution reactions on aromatic and heteroaromatic rings evidence for addition and substitution mechanism

Abstract Irradiation of a cyclohexane solution of hexafluorobenzene in the presence of benzophenone resulted in both, substitution and addition products. Similar photoreaction has been observed by irradiation of hexafluorobenzene in some alcohols in the presence of benzophenone. The reaction of pentafluorobenzene with methanol or cyclohexane resulted in the substitution of a 2-or 4-fluoro atom, while the reaction of pentafluoroanisole resulted in the formation of o-, m- and p-isomers. Irradiation of a cyclohexane solution or of an alcohol solution of octafluoronaphthalene yielded 1- and 2-substituted products. On the other hand, the photosubstitution of fluorine atom in pentafluoropyridine took place exclusively at the position four, thus forming 4-cyclohexyl or 4-(1-hydroxyalkyl) substituted products.

Photoreduction of 1,1-diphenyl-2-haloethenes by metal hydrides

Abstract The nature of the photochemical carbon - halogen bond cleavage in the presence of sodium borohydride or lithium aluminium hydride as reducing agents was studied when a halogen atom is bonded to the sp2 hybridized carbon atom, which is a part of a vinyl system. Irradiation of 1,1-diphenyl-2-bromoethene, or 1,1-diphenyl-2-chloroethene, in the presence of the metal hydrides resulted in an increased formation of the photoreduced product 1,1-diphenylethene in comparison to reactions run in their absence. Conversion of the starting compound and the products distribution depended on the halogen atom bonded, the reducing agent, and the solvent used.

Photochemistry of α-fluorocycloalkanones and α-bromo-α-fluorocycloalkanones

Abstract Uv irradiation of a cyclohexane solution of 2-fluoro-1-indanone, 2-fluoro-1-tetralone, or 2-fluoro-1-benzosuberone resulted in the formation of a radical product (1-indanone, 1-tetralone, or 1-benzosuberone), and the degree of conversion depended on the ring size of the cycloalkanone. On the other hand, both radical as well as ionic products were formed when 2-bromo-2-fluoro derivatives of 1-indanone, 1-tetralone, or 1-benzosuberone were irradiated.

Photochemistry of organo-halogenic molecules. Part 20. The effect of cycloalkene structure on the [2 + 2] photocycloaddition to hexafluorobenzene

The stereochemistry of photocycloaddition reactions of various cycloalkenes to hexafluorobenzene in cyclohexane solution depends on the structure of the cycloalkene, and [2 + 2] cycloadducts are mainly observed. [1,3]-Photocycloaddition is observed only when a large excess of the cycloalkene is used (hexafluorobenzene: cyclopentene, 1 :8) and at higher concentrations. Photoreactions with indene and 1,2-dihydronaphthalene occur stereospecifically syn, and a cis–syn–cis[2 + 2] cycloadduct is isolated. The photocycloaddition reaction with norbornene proceed exclusively exo, with preferential syn addition accompanied by 5%anti-addition. The stereochemistry of the [2 + 2]-photocycloaddition reactions is changed completely in the case of cyclopentene, where 85%anti addition is observed. The course of anti-photocycloaddition diminishes with increasing ring size of the cycloalkene until in the case of cyclooctene, it is reduced to 53%. The quantum yields of [2 + 2]-photocycloadditions, depend on the structure of the cycloalkene and on the concentration of hexafluorobenzene, the greatest effect being observed during [2 + 2]-cycloaddition with indene.

Regio and stereospecificity of solvent photoaddition to 5-fluorouracil and 1,3-dimethyl-5-fluorouracil

Abstract Irradiation of 1,3-dimethyl-5-fluorouracil in methanol, ethanol, water, and acetic acid, and 5-fluorouracil in water at 253.7nm resulted in the formation of two addition products. Regiospecifity was in all cases the same, with functionalization at position 6, while the stereochemistry of addition depended on the solvent. In water preferential trans addition proceeded, while in acetic acid cis addition was predominant. Photoconversion of staring material was also twofold increased in acetic acid, compared to that in water. R = H, CH 3 , CH 2 CH 3 , CH 3 CO R 1 = H, CH 3