2,2′‐Homocoupled Azine N,N′‐Dioxides or Azine N‐Oxides: CDC‐ or SNAr‐Controlled Chemoselectivity

Abstract

An unprecedented Cu(OAc)2‐ and LiOtBu‐mediated homocoupling of azine N‐oxides to yield 2,2′‐azine N,N′‐dioxides is reported. This is the first instance in which copper has been used to catalyze the homodimerization reaction, especially of 2‐phenylpyridine N‐oxides. In the absence of catalytic copper, the reaction follows an alternative pathway, and instead of dioxides it yields 2,2′‐azine N‐monoxides. This latter protocol works efficiently with a range of N‐heterocyclic oxides of pyridine, 2‐phenylpyridine, quinoline and N‐aryl‐1,2,3‐triazole. It is scalable, offers high regioselectivity and gives the products in moderate to high yields. The observed chemoselectivity between the copper‐assisted and copper‐free protocols is routed through oxidative cross‐dehydrogenative coupling (CDC) and nucleophilic aromatic substitution of hydrogen (SNAr) pathways, respectively.