Sustainable, Oxidative, and Metal-Free Annulation

Annulation has received steadily growing interest in the interplay with the increasing emphasis towards selective C−H bond functionalization reactions. Metal-free oxidative annulation through functionalization of inert and abundant C−H bonds offers great improvements in terms of atom- and step-economics as well as reduced waste production under mild reaction conditions. Annulation is considered to be a highly efficient strategy for the construction of cyclic molecules because at least two new bonds are formed within a single reaction step. The combination of annulation and direct C−H bond functionalization allows the efficient and straightforward synthesis of carbo- and heterocyclic molecules using simple and non-prefunctionalized precursors. This Concept highlights novel strategies and recent breakthroughs for metal-free annulation through C−H bond functionalization giving access to a variety of important structural motifs. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim