The Slow Rearrangement of a Sterically Hindered Nitro‐Cyclohexadienone and the Absence of Phenol Oxidation by Nitrogen Monoxide

The exposure of 2,4,6‐tri‐ tert ‐butylphenol ( 1 ) in solution to NO 2 · results in the rapid formation of 2,4,6‐tri‐ tert ‐butyl‐4‐nitro‐2,5‐cyclohexadienone ( 2 ), which then undergoes a slow (ca. 3 d) rearrangement in the absence of air. The mechanism that describes this rearrangement is understood for the first time and involves the initial isomerization of 2 to form a(–ONO)‐substituted cyclohexadieneone ( 6 ). The nitrite moiety undergoes bond homolysis releasing NO · while forming an oxyl radical intermediate. An intermolecular, concerted hydrogen abstraction, which proceeds between 6 and this oxyl radical, results in the simultaneous formation of all stable products, some of which have not been previously observed. Furthermore, when 1 is exposed to NO · under anaerobic conditions, no reaction is observed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)