Thermal and Photochemical Cycloelimination of Nitrogen

Cyclic azo compounds including heteroaromatics with a NN bond of strong double‐bond character can eliminate molecular nitrogen on addition of sufficient thermal energy or on electronic excitation. Some substrates decompose spontaneously, others are moderately or even extremely resistant to N2‐elimination. From a preparative point of view this type of reaction opens a variety of interesting possibilities, e.g. the synthesis of small carbocycles or heterocycles, strained bi‐ and polycycles, as well as cage compounds. From a theoretical mechanistic viewpoint, current importance attaches to the primary fragments such as carbenes, diradicals, trimethylene, trimethylenemethane, dipoles, ylides, antiaromatic 4π‐systems, unstable cycloalkynes, and arynes.