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A new approach to the synthesis of fused 1,2,3-thiaselenazoles-rare five-membered heterocycles that contain two different chalcogens-from the corresponding 1,2,3-dithiazoles and SeO2 was accomplished by selective exchange of S and Se atoms. The fused carbo- and heterocyclic units were indene, naphthalenone, cyclohexadienone, cyclopentadiene, benzoannulene, and benzoxazine. The molecular structures of two of the thiaselenadiazole products and one of the dithiazole precursors were confirmed by single-crystal X-ray diffraction. The reaction is highly solvent selective; it only takes place in solvents that contain a C=O group (e.g., DMF or tetramethylurea). According to DFT calculations, the reaction is thermodynamically favorable. Based on the DFT calculations and 77Se NMR spectroscopy, two tentative mechanisms that feature isomeric transition states and intermediates are suggested for the reaction via ring-opening addition of SeO2 to the S−X dithiazole bond (X=N or S). The DFT-calculated first adiabatic electron affinities of the compounds were chalcogen independent and positive in all cases, which assumes formation of thermodynamically stable radical anions (RAs). These calculated RAs featured either normal or abnormal elongation of the S1−X2 (X=S or Se) bond relative to their neutral precursors and possessed π* or σ* SOMOs, respectively. [ABSTRACT FROM AUTHOR]

Photochemistry of three 6′-cyanosubstituted spironaphthooxazines (SNO) in ethanol matrices at 77 K was studied by means of ultraviolet (UV) and erythrocyte sedimentation rate (ESR) spectroscopy and quantum chemistry. The quantum yield of the open form photolysis is found to be 0.01-0.02, which is high enough for 77 K. For one of the SNO, the formation of a merocyanine form radical was observed. The radicals were formed by an H atom abstraction from the solvent molecule to the light-excited merocyanine isomers. The formation of a merocyanine radical represents a new specific channel of photochemically induced degradation of spirooxazines. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

To elucidate the multifaceted but pooly understood chemistry of the pivotal polysulfur-nitrogen heterocycle, tetrasulfur tetranitride (S4N4, 1), its photochemistry was studied in Ar matrices. Thereby two primary intermediates and a secondary one (2-4) were detected, and their UV-vis and IR spectra were identified throughspecific interconversions of 1-4 that can be induced by selective irradiations. The structures associated with these spectra were assigned with the help of OFT calculations. From these assignments it follows that, under the conditions of the present experiments, the cage structure of 1 transforms into isomeric structures 2-4, one of which is a boat-shaped 8-membered cycle (2), and the two other are novel 6-membered S3N3 cycles carrying exocyclic (N)-SN (3) or (S)-NS (4) groups, respectively, which have not been previously described. These three intermediates probably play a pivotal role in the formation of the diverse products that are observed in the reactions of S4N4 even under mild reaction conditions. [ABSTRACT FROM AUTHOR]