Remote C-H Bond Functionalizations. Группа авторов

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1 Introduction

       Uttam Dutta, Srimanta Guin, and Debabrata Maiti

       Indian Institute of Technology Bombay, Department of Chemistry, Powai, Mumbai, 400076, India

Innovation and implementation of science and technology is a defining parameter to determine the progress of a civilization. Inquisitive minds are constantly devoted in empowering the human civilization by elegant discoveries and their subsequent applications in practical life. Organic chemistry, being a prime component of modern science, has served the human society in a way that has pronounced to be a boon for the present era. In one hand organic chemistry has unfolded the mechanistic intricacies of biorelevant reactivity, while on the other hand it has uncovered the methods to synthesize the molecular architecture that can either mimic the biological activity or can alter the same. Additionally, organic chemistry has profound industrial application including agrochemicals, food industry, dyes industry, polymer industry, and so on. As a whole, organic chemistry has become an inseparable component in our daily life. However, the genesis of these applications and large scale synthesis used to be initiated at synthetic laboratory. The ground breaking discoveries by erudite chemist have thus proved the intellectual supremacy of human race. However, the efficacy of synthetic methods is dependent on the step economy, atom economy, and environment benignity. Never ending aspiration to search such fruitful methods continues to challenge the chemist and inspire new chemical transformations. Accounting these existing literature precedents in the form of a concise summary, which would be the tutorial resources for future generation to accomplish successive progress, is undeniably one of the best efforts to intensify the expansion of chemical synthesis.

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      Chapter 2 introduces to the realm of directing group (DG) assisted distal arene meta‐functionalization. Precise control on regioselectivity is one of the most important aspects in arene C–H functionalization. Arenes bearing heteroatom containing functionality, which is famously known as directing group (DG), were extensively exploited for proximal ortho‐C–H activation. Extending such DG‐assisted distal meta‐functionalization strategy required proper template engineering that would ensure the meta‐selective C–H activation. In this context, Yu and coworkers disclosed a “U”‐shaped template for meta‐selective alkenylation. Thereafter, Yu, Maiti, Tan, Li, and others embarked on exploring the scope of meta‐functionalizations employing several templates. Gao and Li have collectively penned down in delineating a monograph on recent development of transition metal‐catalyzed, template assisted distal meta‐C–H functionalization.

      Chapter 3 deals with the involvement of the Catellani reaction for distal functionalization of (pseudo)halo arenes. Transition metal‐catalyzed cross‐coupling reactions have revolutionized the art of modern synthesis. While aryl halides or pseudohalides produced ipso‐functionalized compounds, a new class of reactivity of aryl (pseudo)halide was developed by Catellani utilizing the combination of strained bicyclic olefin, norbornene (NBE), and palladium. A phenylnorbornylpalladium(II) (PNP) dimeric Pd‐catalyst was successfully employed to furnish o,o′‐disubstituted vinylarenes starting from aryl iodides, alkyl iodide, and olefin in a regioselective manner. This Pd–NBE cooperative catalysis was expanded further for a diverse class of substrates including NH‐indoles and NH‐pyrroles, arenes bearing directing group (DG), and arylboron compounds by several eminent scientists. Several electrophiles were utilized for ortho‐functionalization, and various nucleophiles were used as terminating reagent for ipso‐functionalization. In Chapter 3, Juntao Ye and Mark Lautens have provided a vivid description about the development of arene C–H functionalization relying on Pd–NBE catalysis. The discussion was initially focused on the processes initiated with Pd(0) and subsequent discussion was made on the protocols initiated with Pd(II). However, a large part of Chapter 3 was devoted in portraying synthetic applicability of the Pd–NBE cooperative catalysis.

The seminal work by Catellani on di‐functionalization of aryl (pseudo)halides evolved in 1997. In later years, enormous efforts have been devoted in expanding the scope of this Pd–NBE cooperative catalysis in a relayed C–H activation process. In this context, Dong and Yu independently pioneered a directing group assisted meta‐C–H functionalization utilizing the concept of Catellani reaction. An ortho‐directing group was employed for initial ortho‐C–H activation and subsequent palladium relay was realized in presence of NBE to accomplish meta‐selective arene‐C–H functionalizations. While the directing group (DG) assisted C–H functionalization was extensively studied for ortho‐functionalization, aforementioned seminal reports opened up a new horizon in distal meta‐C–H functionalization. Cheng and Zhou discussed about the recent advancements on directing group assisted meta‐selective functionalization of arenes relying on NBE mediated Catellani type reaction. A detailed discussion was made on various functionalizations including alkylation, arylation, alkynylation, chlorination, and amination, which were achieved by anchoring different ortho‐directing groups such as amides, amines, pyridine, or even free carboxylic acid.

      In Chapter 5, a comprehensive summary on ruthenium catalyzed distal meta‐ and para‐C–H functionalization was provided by Ackermann and coworkers. In last decades a number of handful synthetic protocols were developed to accomplish remote arene C–H functionalization by Ru‐catalysis. Ru‐catalyzed ortho‐C–H ruthenation and subsequent ortho‐functionalization were known in literature over few decades. In a sharp contrast, a unique catalytic reactivity to furnish meta‐functionalized product from such ortho‐ruthenated arenes was first observed by Frost and Ackermann in 2011 and 2013, respectively. In later years, Ackermann, Frost, Greaney, Zhang, and others successfully demonstrated a number of useful meta‐functionalization methods relying on similar strategy. Ru‐catalyzed para‐selective functionalization was also included in Chapter 5 to retrospect the СКАЧАТЬ