Hyperbromide-Mediated Multi-C-H Bond Activations

A combination of attenuated reactivity and lack of selectivity of inert C-H bonds of alkanes and arenes is one of the major challenges that organic chemistry faces today. Consequently, a great deal of research effort has been focused on C-H bond activation as a highly attractive and powerful strategy over the past decade. A common goal of C-H activation chemistry is to functionalize the arene or alkane substrate to a synthetically useful product, and in this case, the C-H bond is regarded as a dormant functional group that can be activated when necessary during the synthetic strategy. In addition to providing an atom economical alternative to standard cross-coupling strategies, C-H bond functionalization also reduces the production of toxic byproducts, thereby contributing to the growing field of reactions with decreased environmental impact.Amongst the recent methodological advances, transition-metal mediated C-H activation processes occupy a commanding position and have been well-studied. However, there are many drawbacks, such as the reagents are generally expensive and air- or moisture-sensitive, it requires the removal of the metal impurity from the products, their substrates are generally in a limited scope. Moreover, the processes still require the ’prefunctionalization’ of starting materials, and have not been in the most economic ways yet.Recently, halide-catalyzed oxidative cross-dehydrogenative coupling reactions (HCDC) have increasingly been developed for its metal-free conditions which maximize resource efficiency, energy efficiency, operational simplicity, and environmental health and safety. In this field, many manifold and highly interesting chemistries of hypervalent iodine compounds are discovered by chemists. While as an important alternative to iodine, hypervalent bromine has also received considerable attention.Inspired of this fast-growing field of research, we report herein a hypervalent bromine-mediated oxidative annulation to furnish 2-heterocycle substituted 1-naphthalenol in which bromobenzene and K2S2O8 were used to active sp, sp2, sp3 C-H bonds simultaneously to construct a new aromatic structure of naphthol, and a method for the regioselective bromination of 2-aminopyridines which is suitable for different types of 2-aminopyridines.Both of these two methods can gave the desired products regioselectively in one step, and have wide scope of substrates. Their metal-free, mild, safe, and environmentally benign characteristics accord with the principle of green chemistry. Undoubtly, these reactions will provide simpler alternatives to tranditional transformation of chemicals and will be important complement for transition-metal mediated activation of C-H bonds.