Traceless Directing Groups in Sustainable Metal-Catalyzed C–H Activation

Abstract

Sustainable transformations towards the production of valuable chemicals constantly attract interest, both in terms of academic and applied research. C–H activation has long been scrutinized in this regard, given that it offers a straightforward pathway to prepare compounds of great significance. In this context, directing groups (DG) have paved the way for chemical transformations that had not been achievable using traditional reactions. Few steps, high yields, selectivity and activation of inert substrates are some of the invaluable assets of directed catalysis. Additionally, the employment of traceless directing groups (TDG) greatly improves and simplifies this strategy, enabling the realization of multi-step reactions in one-pot, cascade procedures. Cheap, abundant, readily available transition metal salts and complexes can catalyze a plethora of reactions employing TDGs, usually under low catalyst loadings—rarely under stoichiometric amounts, leading in greater atom economy and milder conditions with increased yields and step-economy. This review article summarizes all the work done on TDG-assisted catalysis with manganese, iron, cobalt, nickel, or copper catalysts, and discusses the structure-activity relationships observed, by presenting the catalytic pathways and range of transformations reported thus far.

Cross‐Dehydrogenative Coupling Reactions between Phenols and Hetarenes: Modern Trends in Cross‐Coupling Chemistry of Phenols

“…The directing group (DG) strategy, or simply the directing strategy, represents a powerful tool for siteselective CÀ H functionalisation in transition metalcatalysed cross-coupling reactions. [54][55][56][57][58][59] The DG guides the metal centre and delivers the catalyst to the proximal CÀ H bond of the starting substrate, thus controlling the regioselectivity and increasing the reactivity of the position ortho to the DG. Despite these advantages, additional synthetic steps are often required to both incorporate the DG into the starting material and manipulate it after CÀ H functionalisation.…”

“…The directing group (DG) strategy, or simply the directing strategy, represents a powerful tool for site‐selective C−H functionalisation in transition metal‐catalysed cross‐coupling reactions [54–59] . The DG guides the metal centre and delivers the catalyst to the proximal C−H bond of the starting substrate, thus controlling the regioselectivity and increasing the reactivity of the position ortho to the DG.…”

The Pyridotriazole Works as a Traceless Directing Group: A C–H Activation/Annulation Cascade Reaction with Iodonium Ylides

“…Transition-metal-catalyzed C–H activation using a traceless directing group (TDG) represents an attractive strategy with high step- and atom-economy. , This strategy enables the realization of a multistep reaction in one pot, which has assisted in exploring new transformations and concise synthetic routes compared to conventional pathways. In the last few decades, although a lot of TDGs have been reported such as carboxylic acids, , aldehydes, , N -oxides, , nitrones, , N -nitroso amines, amides, and sulfoxonium ylides (Scheme b), new TDGs are still pressingly needed.…”

Synthesis of Indenone Derivatives by Rh(III)-Catalyzed C–H Functionalization of Sulfoxonium Ylides with 1,3-Diynes

“…In recent years, transition-metal-catalyzed traceless DG-assisted C–H functionalizations have gained considerable synthetic importance due to their unique property, which can be easily autocleaved in situ during the reaction without the need for any additional removal steps . In this scenario, several traceless DGs are well studied; among them, sulfoxonium ylide has a significant impact because of its high flexibility and diversity of participation in various annulations such as [4 + 2], [4 + 1], and [3 + 3] .…”