Amination with Oximes

Abstract

AbstractThe SN2 reaction has been well recognized not to occur at sp2 carbons, while such an SN2‐type substitution reaction was found to proceed readily at the sp2 nitrogen of oximes. Ab initio MP2 calculations show that the activation energy of the nucleophilic substitution at sp2 nitrogen is almost same as that of the Beckmann rearrangement. By the intramolecular SN2‐type reaction at the oxime nitrogen, various aza‐arenes and cyclic imines, such as quinolines, aza‐spiro compounds, and dihydropyrroles, can be synthesized. Intermolecular substitution of oximes with organometallic reagents also proceeds, and electrophilic amination of Grignard reagents is accomplished by the use of 4,4,5,5‐tetramethyl‐1,3‐dioxolan‐2‐one O‐(phenylsulfonyl)oxime. Anion radicals generated by one‐electron reduction of oxime derivatives act as iminyl radical equivalents. That is, the intramolecular C–N bond formation of γ,δ‐unsaturated or β‐aryl oximes is induced by a single electron transfer to give various pyrroles, quinolines, and carbolines, in which phenols, hydroquinones, or copper reagents can be used as electron donors. A photo‐induced radical process is also applied to the transformation of γ,δ‐unsaturated oximes to dihydropyrroles. Oxidative addition of oximes to palladium(0) complexes generates alkylideneaminopalladium(II) species, which are utilized as key intermediates in carbon–nitrogen bond formation. Various aza‐heterocycles, including pyrroles, pyridines, isoquinolines, spiroimines, and aza‐azulenes, are synthesized from O‐(pentafluorobenzoyl)oximes having olefinic moieties via the intramolecular Heck‐type reaction (amino‐Heck reaction) by treatment with a catalytic amount of a Pd0 complex. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)