Preparative Scale Applications of C−H Activation in Medicinal Chemistry

C−H activation is an attractive methodology to increase molecular complexity without requiring substrate prefunctionalization. In contrast to well-established cross-coupling methods, C−H activation is less explored on large scales and its use in the production of pharmaceuticals faces substantial hurdles. However, the inherent advantages, such as shorter synthetic routes and simpler starting materials, motivate medicinal chemists and process chemists to overcome these challenges, and exploit C−H activation steps for the synthesis of pharmaceutically relevant compounds. In this review, we will cover examples of drugs/drug candidates where C−H activation has been implemented on a preparative synthetic scale (range between 355 mg and 130 kg). The optimization processes will be described, and each example will be examined in terms of its advantages and disadvantages, providing the reader with an in-depth understanding of the challenges and potential of C−H activation methodologies in the production of pharmaceuticals.     

The B-Alkyl Suzuki-Miyaura Cross-Coupling Reaction: Development,Mechanistic Study,and Applications in Natural Product Synthesis A list of abbreviations can be found at the end of the article

The development of new reactions that facilitate the creative and efficient synthesis of molecular structures with desirable properties continues to fascinate chemists. The test of a significant contribution is its acceptance over time by the scientific community. The B-alkyl Suzuki-Miyaura cross-coupling reaction appears to be one such reaction. Since its disclosure by Suzuki and Miyaura in 1986, this reaction has been an attractive solution to challenging synthetic problems.     

Transition Metals in the Synthesis and Functionalization of Indoles [New Synthesis Methods (72)]

The use of transition-metal complexes as reagents for the synthesis of complex organic compounds has been under development for at least several decades, and many extraordinary organic transformations of profound potential have been realized. However, adoption of this chemistry by the practicing synthetic organic chemist has been inordinately slow, and only now are transition-metal reagents beginning to achieve their rightful place in the arsenal of organic synthesis. Several factors contributed to the initial reluctance of synthetic organic chemists to use organometallic reagents. Lacking education and experience in the ways of elements having d electrons, synthetic chemists viewed organometallic processes as something mysterious and unpredictable, and not to be discussed in polite society. Organometallic chemists did not help matters by advertising their latest advances as useful synthetic methodology, but restricting their studies to very simple organic systems lacking any serious functionality (e.g., the “methyl, ethyl, butyl, futile” syndrome). Happily, things have changed. Organometallic chemists have turned their attention to more complex systems, and more recently trained organic chemists have benefited from exposure to the application of transition metals. This combination has set the stage for major advances in the use of transition metals in the synthesis of complex organic compounds. This review deals with one aspect of this area, the use of transition metals in the synthesis of indoles.     

Biaryl monophosphine ligands in palladium-catalyzed C–N coupling: An updated User's guide

Over the past three decades, Pd-catalyzed cross-coupling reactions have become a mainstay of organic synthesis. In particular, catalysts derived from biaryl monophosphines have shown wide utility in forming C–N bonds under mild reaction conditions. This work summarizes a variety of C–N cross-coupling reactions using biaryl monophosphines as supporting ligands, with the goal of directing synthetic chemists towards the ligands and conditions best suited for a particular coupling.PreludeWhen I learned that I had received the 2018 Tetrahedron Prize for Creativity in Organic Chemistry, jointly with Professor John F. Hartwig of UC Berkeley, I felt a sense of great accomplishment. Accomplishment not specifically for me, but by my research group (and that of John's) in developing new chemistry that was both intrinsically interesting and of practical utility. The latter aspect is the reason that we have chosen to write this review to help practitioners in the field utilize palladium-catalyzed C–N coupling reactions more broadly, efficiently, and predictively in their own research efforts. We note that while we have limited this review to reactions using biaryl phosphine ligands, that many other good alternatives exist.     

Recent developments in natural product synthesis using metal-catalysed C-H bond functionalisation

Metal-catalysed C-H bond functionalisation has had a significant impact on how chemists make molecules. Translating the methodological developments to their use in the assembly of complex natural products is an important challenge for the continued advancement of chemical synthesis. In this tutorial review, we describe selected recent examples of how the metal-catalysed C-H bond functionalisation has been able to positively affect the synthesis of natural products.     

Catalysts for cross-coupling reactions with non-activated alkyl halides

Despite the problems inherent to metal-catalyzed cross-coupling reactions with alkyl halides, these reactions have become increasingly important during the last few years. Detailed mechanistic investigations have led to a variety of novel procedures for the selective cross-coupling of non-activated alkyl halides bearing beta hydrogen atoms with a variety of organometallic nucleophiles under mild reaction conditions. This Minireview highlights selected examples of metal-catalyzed coupling methods and is intended to encourage chemists to exploit the potential of these approaches in organic synthesis.     

Palladium-catalyzed cross-coupling reactions of aryl mesylates

Palladium-catalyzed cross-coupling reactions are state-of-the art methods for synthesis of many important compounds. The development of the use of the phenol-derived sulfonated hydroxyl group in the coupling reactions is highly attractive as the hydroxyl group is commonly present in organic compounds and they are versatile alternatives to aryl halides in cross-coupling reactions. In this tutorial review, we summarize the current development of palladium-catalyzed cross-coupling reactions of aryl mesylates.     

Asymmetric transfer hydrogenation: chiral ligands and applications

Hydrogen transfer reduction processes are attracting increasing interest from synthetic chemists in view of their operational simplicity and high selectivity. In this tutorial review the most significant advances recently achieved in the stereoselective reduction of unsaturated organic compounds catalyzed by homogeneous transition metal complexes are critically reviewed. A sharp growth of the synthetic applications of this technique in the synthesis of fine chemicals is predictable as the use of transition metal catalyzed reactions will become more familiar to synthetic chemists.     

钯催化的交叉偶联反应——2010年诺贝尔化学奖获奖工作介绍

钯催化的交叉偶联反应是非常实用的合成新方法.文章给出了Heck反应、Negishi反应和Suzuki反应的概念,对其反应机理作了详细的说明,并对其在复杂化合物和天然产物全合成中的应用作了评价.     

The Pauson-Khand reaction, a powerful synthetic tool for the synthesis of complex molecules

There are still some synthetic chemists who hesitate to use metal-mediated or -catalysed reactions. The Pauson-Khand reaction (PKR) is a powerful transformation that has now been sufficiently well developed to be routinely considered when planning a synthesis, especially of polycyclic complex molecules. This tutorial review aims to encourage the use of this process explaining the best ways of performing a PKR both in the stoichiometric and the catalytic version, showing the scope of the process and its limitations. Additionally, asymmetry can be introduced in the reaction using several strategies, which will be discussed. The most recent examples of the synthetic applications of the PKR in natural product synthesis will give the reader an idea of the great usefulness of this reaction.     

Cross-coupling in flow

Until recently, cross-coupling reactions have been exclusively performed in batch processes. With the advent of microfluidics, significant effort has been devoted to develop a wide variety of continuous-flow techniques to facilitate organic synthesis. In this critical review, we attempt to give an overview of the different continuous-flow methodologies that have been developed and utilized for cross-coupling reactions. In addition, we attempt to point out the advantages of continuous-flow when compared with their batch counterparts (246 references).     

Review of Synthesis of Spiro Heterocyclic Compounds from Isatin

Isatin is an essential building block in organic synthesis and shows various biological activities. The most attractive application of isatin in organic synthesis is undoubtedly in the highly reactive C-3 carbonyl group, which is a prochiral center as well. The construction of a spiroheterocyclic framework has always been a challenging endeavor for synthetic organic chemists as it frequently requires synthetic design based on specific strategies. This review gives a short summary of the advances in the use of isatin in the synthesis of various spiroheterocyclic compounds through multicomponent reactions and 1,3-dipolar cycloaddition reactions.     

Room-Temperature Arylation of Thiols: Breakthrough with Aryl Chlorides

The formation of aryl C−S bonds is an important chemical transformation because aryl sulfides are valuable building blocks for the synthesis of biologically and pharmaceutically active molecules and organic materials. Aryl sulfides have traditionally been synthesized through the transition-metal-catalyzed cross-coupling of aryl halides with thiols. However, the aryl halides used are usually bromides and iodides; readily available, low-cost aryl chlorides often not reactive enough. Furthermore, the deactivation of transition-metal catalysts by thiols has forced chemists to use high catalyst loadings, specially designed ligands, high temperatures, and/or strong bases, thus leading to high costs and the incompatibility of some functional groups. Herein, we describe a simple and efficient visible-light photoredox arylation of thiols with aryl halides at room temperature. More importantly, various aryl chlorides are also effective arylation reagents under the present conditions.     

Synthesizing optoelectronic heteroaromatic conjugated polymers by cross-coupling reactions

Heteroaromatics-containing polymers comprise a huge class of materials that have received considerable attention due to their interesting electrical, electrochemical, and optical properties. In this review, the recent advances on the use of organometallic cross-coupling reactions for the synthesis of heteroaromatic conjugated polymers for the optoelectronic interests and applications are summarised.     

Oligosaccharide assembly by one-pot multi-step strategy

Saccharide synthesis is a formidable task for synthetic chemists. Although in recent years many advances have been made in this area, development of more convenient and efficient strategies for oligosaccharide synthesis is still in great demand. This review focuses on one of these new strategies--the one-pot sequential glycosylation approach as a potent tool for oligosaccharide assembly.     

Ultrasound irradiation in heterocycle synthesis: An overview

The synthesis of heterocyclic compounds has been a hot topic for several decades. Synthetic organic chemists are always in search of new methodologies which are greener for the synthesis of heterocyclic compounds. The ultrasound-assisted reactions have contributed much to this field. This review focuses on the impact of sonochemistry in the synthesis of heterocyclic compounds and covers the literature from 2009 to 2020.     

Free Carboxylic Acids: The Trend of Radical Decarboxylative Functionalization

The exceptional versatility of carboxylic acids has been extensively exploited in organic synthesis across several decades. There has been a recent upsurge of radical decarboxylative transformations. The process can be initiated under mild conditions, and the resultant radicals have orthogonal reactivities to closed-shell species, thus providing immense opportunities for streamlining novel reactions. The use of free carboxylic acids is the most desirable owing to its high atom and step economy. Aiming to demonstrate the attractiveness of the strategy and to inspire chemists to tackle existing challenges, this review outlines the recent advances on radical decarboxylative functionalization of free carboxylic acids.     

New Developments in the Chemistry of Low-Valent Titanium

Among the applications of low-valent titanium in organic synthesis, the reductive coupling of carbonyl compounds to produce alkenes (the McMurry reaction) is particularly prominent. Discovered at the beginning of the 1970s, it has been developed and tested repeatedly, for example in numerous syntheses of natural products. This alkene synthesis has become a standard reaction in the repertoire of preparative chemists. However, the possibilities of low-valent titanium are by no means limited to this process: the last few years have brought some spectacular applications of the conventional McMurry reaction (for example the synthesis of taxol) along with a considerable extension of the scope of reductive carbonyl couplings. Thus, diverse heterocycles are now accessible following novel and efficient pathways based on intramolecular cross-coupling of functional groups—some of which were hitherto considered to be inert to titanium. The use of this method for the synthesis of indole and pyrrole alkaloids illustrates the new possibilities. At the same time, considerably simplified methods for conducting McMurrytype reactions have been developed. Examples include the particularly convenient “instant” method, the first ketone–amide coupling reactions requiring only catalytic amounts of titanium salts, and the first application of commercially available titanium powder as a coupling agent. Last but not least, the detailed investigation of diverse classical McMurry reagents has afforded a deeper understanding of the nature and mode of action of low-valent titanium. Revision of some of the current conceptions of the process of reductive carbonyl coupling is thus indispensable.     

Microwave-Assisted Synthesis: Can Transition Metal Complexes Take Advantage of This “Green” Method?

Microwave-assisted synthesis is considered environmental-friendly and, therefore, in agreement with the principles of green chemistry. This form of energy has been employed extensively and successfully in organic synthesis also in the case of metal-catalyzed synthetic procedures. However, it has been less widely exploited in the synthesis of metal complexes. As microwave irradiation has been proving its utility as both a time-saving procedure and an alternative way to carry on tricky transformations, its use can help inorganic chemists, too. This review focuses on the use of microwave irradiation in the preparation of transition metal complexes and organometallic compounds and also includes new, unpublished results. The syntheses of the compounds are described following the group of the periodic table to which the contained metal belongs. A general overview of the results from over 150 papers points out that microwaves can be a useful synthetic tool for inorganic chemists, reducing dramatically the reaction times with respect to traditional heating. This is often accompanied by a more limited risk of decomposition of reagents or products by an increase in yield, purity, and (sometimes) selectivity. In any case, thermal control is operative, whereas nonthermal or specific microwave effects seem to be absent.     

Synergistic Pd/Cu Catalysis in Organic Synthesis

Synergistic Pd/Cu catalysis has been utilized in the Sonogashira reaction since 1975. However, this strategy has not received much attention from the organic chemist community until recently. Synergistic Pd/Cu catalysis is becoming a proficient method for the development of catalytic reactions, including several new and efficient cross-coupling reactions. Additionally, several challenging asymmetric reactions, including stereodivergent synthesis, have been discovered by the combined use of a chiral metal catalyst and a second achiral metal catalyst or two chiral metal catalysts. This review provides an overview of this field, with the aims of highlighting both the development of synergistic Pd/Cu catalysis in organic synthesis and the reaction mechanisms involved in this research area.