Recent Developments in the Chemistry of Heteroaromatic N-Oxides

Selected developments in the chemistry of heteroaromatic N-oxides since 2001 are presented in this review. The use of these N-oxides, both in late-transition-metal-catalyzed oxidations of carbon–carbon triple bonds and in regioselective C–H functionalizations of the heteroarene, are contemporary topics of interest and the focus of the discussion. 1 Introduction 2 Synthesis of Heteroaromatic N-Oxides 2.1 Direct Oxidation of Hindered Heteroarenes 2.2 Through Construction of Heteroaromatic Rings 3 Heteroaromatic N-Oxides as Oxidants 3.1 Alkyne Oxidation 3.2 Allene Oxidation 3.3 Carbene Oxidation 4 Heteroaromatic N-Oxides as Substrates 4.1 Deoxygenative ortho-C–H Functionalization with Prior Activation 4.2 Deoxygenative ortho-C–H Functionalization with Nonstabilized Carbanions 4.3 Nondeoxygenative C–H Functionalization 4.3.1 ortho-C–H Functionalization 4.3.2 N-Oxide Directed ortho-Alkyl C–H Functionalization 4.3.3 N-Oxide Directed Remote C–H Functionalization 4.4 1,3-Dipolar Cycloaddition 5 Conclusion and Outlook