MECHANISM OF THE CYCLOPROPANE WALK REARRANGEMENT - SYNTHESES AND PROPERTIES OF 2-DIAZOPROPANE ARENE ADDUCTS - A REGIOSPECIFIC N-2 ELIMINATION

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 Copyright © 1990 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim