Autocatalytic Radical Ring Opening ofN-Cyclopropyl-N-phenylamines Under Aerobic Conditions − Exclusive Formation of the Unknown Oxygen Adducts,N-(1,2-Dioxolan-3-yl)-N-phenylamines

Abstract

In contrast to the high stability of N-alkyl-N-cyclopropylamine derivatives, N-cyclopropyl-N-phenylamine (1a) has been found to slowly convert into the hitherto unknown product N-(1,2-dioxolan-3-yl)-N-phenylamine (1f) at room temperature under aerobic conditions. The rate of this conversion was found to be significantly increased by the presence of a catalytic amount of the single-electron oxidizing agent tris(1,10-phenanthroline)FeIII hexafluorophosphate or of the hydrogen-abstracting agents benzoyl peroxide or tert-butyl peroxide/UV light. Based on the regio- and stereochemical outcomes of aerobic ring-opening reactions of some specifically ring-methylated derivatives of 1a, namely N-(1-methylcyclopropyl)-N-phenylamine (2a), N-(trans-2-methylcyclopropyl)-N-phenylamine (3a), and N-(cis-2-methylcyclopropyl)-N-phenylamine (4a), as well as other experimental evidence, an autocatalytic mechanism analogous to that of the oxygenation of vinylcyclopropanes is proposed for the formation of the 1,2-dioxolane product. The oxidative radical ring opening and related chemistry of these novel derivatives could be valuable in mechanistic studies of heteroatom-oxidizing enzymes.