Building molecular complexity through transition-metal-catalyzed oxidative annulations/cyclizations: Harnessing the utility of phenols, naphthols and 1,3-dicarbonyl compounds

Transition-metal-catalyzed functionalization of traditionally unreactive carbon-hydrogen bonds offers a versatile and indispensable tool for streamlining the organic synthesis. This facile and powerful strategy enables the synthesis of new and valuable structural motifs of biological interest from readily accessible starting materials avoiding any tedious preactivation (halogenate or borylate), thus enhancing the atom and step-economy of organic synthesis. This review encapsulates the recent developments (2012-2017) in the oxidative annulation/cyclization reactions using various transition-metal catalysts (Ru, Rh, Pd, Ir, Cu, Co, Fe) in the presence of external oxidants. The utility of simple and useful starting materials including phenols, naphthols and 1,3-dicarbonyl compounds employing a diverse array of coupling partners (alkynes, alkenes, 1,3-dienes, allenes, enynes, benzoyl aldehyde oximes, fullerenes) to deliver a broad range of oxygenated heterocycles (benzopyrans, benzoxepines, coumarins, furans, benzofurans, chromenes, benzopyranones, benzoxazoles) and carbocycles (spiroindenes, spiroindanes, spiroenones, spirodialins among many others) is described. In addition, selected examples representing the scope and limitations, combined with the mechanisms of these oxidative annulations are included in the discussion. (C) 2018 Elsevier B.V. All rights reserved.