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1998 photochemistry, radiation chemistry, chemoluminescence photochemistry, radiation chemistry, chemoluminescence O 0160 -046Photochemistry of Fluorophenyl Azides in Diethylamine. Nitrene Reaction versus Ring Expansion.-Fluorophenyl azides are the most popular reagents for photoaffinity labeling. In order to further investigate the fluorine effect on the singlet nitrene ring expansion, several fluorophenyl azides were photolyzed with diethylamine at 25 • C. While most of the compounds afford azepines by ring expansion, in o,o'-difluorosystems such as (XII) a steric repulsion leads to a considerably higher barrier to ring expansion producing hydrazines by singlet phenyl nitrene N-H insertion reactions. -(LEYVA, E.; SAGREDO, R.; Tetrahedron 54 (1998) 26, 7367-7374; Fac. Cienc. Quim., Univ. Auton. San Luis Potosi, San Luis Potosi 78210, Mex.; EN)

Insertion. -The title insertion reaction leading to fluoroazobenzenes, e.g. (IV) and (XII), proceeds predominantly in the case of 2,6-and pentafluorophenyl azides such as (XI). -(LEYVA*, E.; SAGREDO, R.; MOCTEZUMA, E.; J. Fluorine Chem. 125 (2004) 5, 741-747; Fac. Cienc. Quim., Univ. Auton. San Luis Potosi, San Luis Potosi 78210, Mex.; Eng.) -K. Schneider