Zum Mechanismus der Cyclopropan-„Walk”-Umlagerung: Synthese und Eigenschaften von 2-Diazopropan-Aren-Addukten; eine regiospezifische N2-Eliminierung

Mechanism of the Cyclopropane “Walk” Rearrangement: Syntheses and Properties of 2-Diazopropane - Arene Adducts; a Regiospecific N2 Elimination The synthesis and the thermal and photochemical behavior of 2-diazopropane adducts of toluene 1a, m-xylene 1b,c, and Dewar benzene 2a,b are reported. At 60°C the thermal N2 elimination of the specifically deuterated compound 1c proceeds regiospecifically leading to 1,7,7-trimethyl-5-(trideuteriomethyl)-1,3,5-cycloheptatriene (12c), whereas the photolysis of 1c sensitized by benzophenone yields both regioisomeric cycloheptatrienes 12c and 13c in a 51:49 ratio. This finding excludes the symmetrical diradical 3c as an intermediate in the thermal N2 elimination of 1c and suggests a novel pericyclic process for it. The formation of both regioisomeric cycloheptatrienes 25b and 25c in a 74:26 ratio in the thermolysis of the diazopropane-tetradeuterio Dewar benzene adduct 2b indicates that in this case a multi-step N2 elimination passing through the diradical intermediate 3e competes with the concerted process. According to force-field calculations the course of the N2 elimination in 1a-e might be controlled by the conformational equilibrium A⇆B