Reaction of (Arylmethyl)amines with Superoxide Anion Radical in Aprotic Media. Insights into Cytokinin Senescence Inhibtion

The cytokinins are a group of plant senescence retarding phytohormones, usually N-arylmethyl derivatives of adenine. Purine, adenine, and the cytokinins kinetin [6-(furfurylamino)purine] and 6-(benzylamino)purine were reacted with O2- generated from KO2 solubilized in diethylamine by 18-crown-6 polyether. The only reaction observed was simple deprotonation of the N-7 hydrogen, yielding an air-stable salt. In order to uncover other modes that might be available in the absence of this simple acid-base reaction, we reacted various (arylmethyl)amines (i.e., furfurylamine and benzylamine) and (arylmethyl)anilines (2a-c) with 02-. in benzene. The products in the case of (arylmethyl)amines were the corresponding aroylamines isolated in greater than 60% yield. Compounds 2a-c yielded the corresponding amides (3), benzoic acids (4), nitrobenzenes (5), and arenes. Similar results were obtained when tert-butoxide or hydroxide replaced superoxide, with the rate of reaction decreasing in the order t-BuO- > O2 > HO-, the apparent order of decreasing basicity. The results suggest that the process observed involves a base-catalyzed autoxidation of the benzylic carbon of the benzylamines. The resulting hydroperoxide rearranges and/or undergoes oxidative cleavage, ultimately yielding the observed products. Aniline itself reacts with 02”., yielding azobenzene, nitrobenzene, and (4-nitrophenyl)phenylamine. The latter presumably results from the nitrobenzene trapping of the anilinyl radical.