Oxygen, singlet addition reactions

Some of these pathways are also useful for explaining photolysis of furocoumarins in solution. When a furocoumarin is UV-A-excited in solution in the absence of any substrate, its target may be another furocoumarin molecule (in its ground state) or a solvent molecule. In both cases, a Type III (oxygen-independent) addition reaction occurs. When the solution is aerated, the Type 11 pathway is also involved, and singlet oxygen may oxidize a psoralen molecule. ... 

SCHEME 1. [4 + 2], [2 + 2] and ene addition reactions of singlet molecular oxygen to alkenes... 

The direct photoisomerizations are singlet-state reactions, as shown by their independence of oxygen and the addition of triplet quenchers. Ilge et a/.31 103 demonstrated that no potential barriers in the photoisomerizations, EE - EZ, and EZ — ZZ, were found. In contrast, there was a small barrier in the photoisomerization of ZZ - EZ or ZE a veiy weak fluorescence was detected at 77 K, and the fluorescence of the ZZ isomer disappeared at temperatures above 130 K. 

This e c o-peroxide rearranged readily to form the /ra s-benzene trioxide 144 and gave trans-benzene dioxide 142 upon reaction with triphenylphosphite. A similar addition reaction occurred between singlet oxygen and indan 8,9-oxide 7 to yield a further endo-peroxide. An endo-peroxide adduct of an oxepin was also formed when singlet oxygen reacted with 1-benzoxepin 100. Upon deoxygenation with trimethylphosphite, the latter peroxide yielded an aldehyde. ... 

Yoshioka, Y., Tsunesada, T., Yamaguchi, K., Saito, I., CASSCF, MP2, and CASMP2 Studies on Addition Reaction of Singlet Molecular Oxygen to Ethylene Molecule, Int. J. Quantum Chem. 1997, 65, 787 801. 

The reactions of 27 and 29 cannot be photosensitized and oxygen has no effect on either reaction. In addition, the observed cyclization and migration reactions are consistent with orbital symmetry considerations only if these are excited electronic state reactions. Consequently, it is felt that these most likely are all excited singlet state reactions. 

K2. Keams, D. R., Selection rules for singlet-oxygen reactions. Concerted addition reactions. J. Am. Chem. Soc. 91, 6554-6563 (1969). 

Recently, there has been an interest shown in the way that hetero-atoms (e.g. nitrogen) interact with singlet oxygen. " The finding that the phos-phorin (21) undergoes an addition reaction with this species is therefore... 

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