Synthetic Semiconductor Photoelectrochemistry.

In addition to electrochemical and photochemical approaches, the photoelectrochemical method using semiconductors as photoelectrodes is a third type of approach in the field of synthetic organic chemistry that enables precise control of single electron transfer (SET) reactions. Herein, we report mechanistic studies on TiO2 photoelectrochemical redox neutral reactions, where both reductive and oxidative SET are involved, using radical cation [2 + 2] cycloadditions as models. In the presence of platinum nanoparticles or molecular oxygen as electron sink or electron acceptor, respectively, the mechanistic details for the photoelectrochemical reactions can be investigated because the excited electron at the conduction band of TiO2 is removed.

Recently, electron has been recognized as the simplest catalyst in the field of synthetic organic chemistry. Addition or removal of electron can activate small molecules for further chemical transformations, which is referred to as redox catalysis. Reductive and/or oxidative single electron transfer (SET) can be induced by means of electro- and photochemistry, where an electron can play a role of catalysts. Radical ions are primarily generated via SET, offering unique reactive intermediates.Distonic radical ions are transient species with formally separated radical and charge cites. They potentially exhibit radical and ion reactivities independently, which may differ from usual radical ions. However, distonic radical ions are not commonly used as reactive intermediates in the field of synthetic organic chemistry, probably because of lack of their simple generation methods.We have been developing oxidative SET-triggered cycloadditions in a lithium perchlorate/nitromethane solution. Radical cations are involved in the reactions as distinctive reactive intermediates, facilitating intermolecular carbon-carbon bond formations. We questioned whether the distonic radical cation can also be generated by oxidative SET, leading to novel chemical transformations. In this presentation, oxidative SET-catalyzed vinylcyclopopane rearrangements will be described. Figure 1

Heterocyclic compounds are an important class of compounds in the field of pharmaceutical and synthetic organic chemistry. The Schiff bases contain azomethine linkages which are obtained by the condensation of aldehyde/ketone with amines. Among the various types of Schiff bases, the chalcone-based Schiff bases play a vital role in the treatment of various ailments and various applications, which can be synthesized by using different types of chalcones as the starting materials. These types of compounds were synthesized by using various techniques like conventional means of synthesis, microwave-assisted reaction, heterocyclic catalyst-mediated synthesis and also by means of trituration. The chalcone or bis-chalcone-based Schiff bases and their derivatives contain -C=N linkage which exhibits various activities including antimicrobial, anticancer, antioxidant, antidiabetic and immunosuppressant activities. Beyond these activities, these types of Schiff bases are also used in various chemical industries and fluorescent sensors, which also play a major role in the field of synthetic organic chemistry and coordination chemistry as intermediates. This review discusses the numerous synthetic strategies along with their applications in the field of medicine. Thus, this review will be helpful in developing more effective drug-like scaffolds for use in future drug design. Keywords: Schiff bases, Chalcone-based Schiff bases, Antimicrobial, Anticancer, Antioxidant, Biological Applications

Explosive growth in the use of open shell reactivity, including neutral radicals and radical ions, in the field of synthetic organic chemistry has been observed in the past decade, particularly since the advent of ruthenium complexes in 2008. These complexes generally induce single-electron transfer (SET) processes via visible-light absorption. Additionally, recent significant advancements in organic electrochemistry involving SET processes to provide open shell reactivity offer a complementary method to traditional polarity-driven reactions described by two-electron transfer processes. In this Review, we highlight the importance of intramolecular SET processes in the field of synthetic organic chemistry, which seem to be more elusive than the intermolecular versions, since they are net redox-neutral and thus cannot simply be regarded as oxidations or reductions. Such intramolecular SET processes can rationally be understood in combination with concomitant bond formations and/or cleavages, and are regulated by a structural motif that we call a "redox tag." In order to describe modern radical-driven reactions involving SET processes, we focus on a classical formalism in which electrons are treated as particles rather than waves, which offers a practical yet powerful approach to explain and/or predict synthetic outcomes.

In the field of synthetic organic chemistry, photochemical and electrochemical methods are often considered to be competing techniques that induce single electron transfer (SET). Recently, metal complexes and organic dyes have been extensively used as molecular sensitizers that can induce homogeneous bidirectional SET. On the other hand, heterogeneous monodirectional SET can be induced by electrodes, which differs from the photochemical methods. In this context, semiconductors are unique alternatives, since they can induce heterogeneous but bidirectional SET, potentially enjoying advantages of both photochemical and electrochemical methods. Such semiconductor "photoelectrochemical" methods may trigger the reactions that are otherwise difficult to achieve.We have been developing electrochemical SET-triggered cycloadditions in lithium perchlorate (LiClO4)/nitromethane (CH3NO2) solution, which facilitates the generation of radical cations from electron-rich alkenes and styrenes. Recently, we also have been focusing on TiO2 photoelectrochemical SET-triggered cycloadditions, expanding a scope of the electrochemical versions. During the course of our study to develop new TiO2 photoelectrochemical SET-triggered cycloadditions, we unexpectedly found that vinylcyclopropane rearrangements was also possible in LiClO4/CH3NO2 solution. The reactions are initiated by oxidative SET by hole, which is followed by immediate ringopening of the cyclopropanes to generate distonic radical cations. It is expected that reductive SET by excited electron is also involved to realize effective net redox-neutral transformations. Experimental details, including preliminary mechanistic studies, will be presented in this talk.

In the periodic table of elements, indium is located within group 13, and has the atomic number 49. Indium is classified as one of the chemical elements of post-transition metals. Indium is silvery-white in color, soft, and possesses a high level of malleability. Although indium is a relatively rare element, it is indispensable in industry applications worldwide. German metallurgists discovered indium in 1863. It was not until the early 1990s, however, that scientists in the field of synthetic organic chemistry attempted genuine studies to explore the roles of indium or indium-related reagents. Focusing on indium or indium-related reagents, many recent investigations have led to significant advances in synthetic organic chemistry. Various applications have been examined and a growing number of useful chemical transformations using indium or indium-related reagents are being revealed and reported. Chemical transformations of the reactive functional groups are an essential point, particularly for the successful implementation of a sequence of multiple-step chemical schemes. For this purpose, a variety of strategic reaction methodologies have been developed, including those utilizing indium or indium-related reagents. Indium metal was discovered to be useful for the protection and deprotection of functional groups, while trivalent indium Lewis acids have been effective in a wide variety of chemical transformations. This chapter describes an efficient oxone-mediated esterification of aldehydes using indium(III) triflate, which is also one of the trivalent indium Lewis acids. Esterification is performed primarily on aromatic and heterocyclic aldehydes. The results show the effectiveness of this esterification methodology and suggest the potential in the further development of these reagents, which could enhance the field of synthetic organic chemistry.

17 - Applications of the Olefin Metathesis Reaction

The advent of photoredox catalysis has created a massive buzz in the field of synthetic organic chemistry. As the photoredox process is invariably mediated by the transfer of single electrons, species such as radical cations are inevitable. These species have orcastracized various synthetic transformations that otherwise would have been difficult to achieve. One such class of transformations is the cycloaddition reaction. For driving such reactions, it is often necessary that the radical and cation sites are present on different atoms, in other words, are distal or “ distonic” in nature. In the present review, the development of distonic radical cations has been brought forth and their tactical exploitation over the years for the purpose of cycloaddition reactions in the visible‐light realm. The entirety of the manuscript has been divided into categories discussing [2 + 2], [3 + 2], and [4 + 2] cycloadditions. In each case, the distonic radical cation that drives the cycloaddition has been highlighted along with necessary discussions, providing readers with an opportunity to appreciate the power of these wonderful intermediates.

Azanucleosides are found to show unique pharmacological activities even without incorporating into oligonucleotides and are used as anticancer and antivirus agents. Practical synthesis routes of azanucleosides are of exceptional importance to enhance the development of (oligo)nucleotide therapeutics. Previously, we reported the synthetic methods of azanucleosides by using electrochemical approaches, which has now been offering green and sustainable redox options in the field of synthetic organic chemistry. However, scaling-up of the reactions remains challenging since continuous production is essentially not possible. Herein, we report the direct anodic N-α hydroxylation of prolinol derivatives as useful intermediates for azanucleosides. Cyclic voltammetry study clearly reveals that the presence of water facilitates the oxidative electron transfer events. The reaction is applicable for large scale production and thus could enhance the development of (oligo)azanucleotide therapeutics.

Although radical ion chain pathways have long been recognized in the field of synthetic organic chemistry and are expected to be operative in various reactions, it is somewhat complicated to verify their involvement, since counting the number of electrons is not straightforward. Herein, a series of bis‐styrenes is designed and synthesized to investigate electron transfer events by using radical cation [4+2] cycloadditions as probes. It is demonstrated that the intramolecular single electron transfer seems to be ineffective, while the intermolecular variants are highly effective. Therefore, a truly catalytic amount of electricity is enough for full conversions, confirming that chain pathways were definitely involved.

In recent years, the most significant development in the field of synthetic organic chemistry has been the application of biological systems to chemical reactions. Reactions catalyzed by enzymes and enzyme systems display far greater specificities than more conventional organic reactions. Biological and/or enzymatic syntheses and transformations, that is, “microbial transformations,” have great potential. Some of these reactions have already been shown to have useful applications in the fields of synthetic organic chemistry and biotechnology. This article reviews the current status of the rapidly developing field of microbial transformation, the methodology, available technological procedures, and fields of application being described especially in relation to conventional organic synthesis methods.

The sulphur centered radicals, produced from various organic compounds, in high efficiency by single-electron-transfer (SET) oxidation. These radicals are highly reactive intermediates having various applications in the construction of organosulphur compounds in the field of synthetic organic chemistry. These S-centred radical-mediated organic transformations have been achieved using photoredox catalysts, including organic dyes and transition metal catalysts, as well as in the absence of any catalyst. Compared with previous methods, photoredox catalysis is inexpensive and features the advantages of being environmentally benign, highly efficient and easy to use. This review focuses on recent developments in the photocatalyzed carbon–sulphur bond formation.

Trifluoromethyl (CF3) and difluoromethyl (CF2H) groups are versatile structural motifs, especially in the fields of pharmaceuticals and agrochemicals. Thus, the development of new protocols for tri- and difluoromethylation of various skeletons has become a vital subject to be studied in the field of synthetic organic chemistry. For the past decades, a variety of fluoromethylating reagents have been developed. In particular, bench-stable and easy-to-use electrophilic fluoromethylating reagents such as the Umemoto, Yagupolskii-Umemoto, Togni, and Hu reagents serve as excellent fluoromethyl sources for ionic and carbenoid reactions. Importantly, the action of catalysis has become a promising strategy for developing new fluoromethylations. For the past several years, photoredox catalysis has emerged as a useful tool for radical reactions through visible-light-induced single-electron-transfer (SET) processes. Commonly used photocatalysts such as [Ru(bpy)3](2+) and fac-[Ir(ppy)3] (bpy = 2,2'-bipyridine; ppy = 2-pyridylphenyl) have potential as one-electron reductants strong enough to reduce those fluoromethylating reagents, resulting in facile generation of the corresponding fluoromethyl radicals. Therefore, if we can design proper reaction systems, efficient and selective radical fluoromethylation would proceed without any sacrificial redox agents, i.e., via a redox-neutral process under mild reaction conditions: irradiation with visible light, including sunlight, below room temperature. It should be noted that examples of catalytic fluoromethylation of compounds with carbon-carbon multiple bonds have been limited until recent years. In this Account, we will focus on our recent research on photoredox-catalyzed fluoromethylation of carbon-carbon multiple bonds. First, choices of the photocatalyst and the fluoromethylating reagent and the basic concept involving a redox-neutral oxidative quenching cycle are explained. Then photocatalytic trifluoromethylation of olefins is discussed mainly. Trifluoromethylative difunctionalization reactions, i.e., simultaneous introduction of the CF3 group and a different functional group across carbon-carbon double bonds, are in the middle of the discussion. Oxy-, amino-, and ketotrifluoromethylation allow us to synthesize various organofluorine compounds bearing C(sp(3))-CF3 bonds. In addition, the synthesis of valuable trifluoromethylated alkenes is also viable when the olefins have an appropriate leaving group or undergo deprotonation. The present reaction system features high functional group compatibility and high regioselectivity. Furthermore, future prospects, especially trifluoromethylative difunctionalization of alkynes and difluoromethylation of alkenes, are also discussed.

In the field of synthetic organic chemistry, the dehalogenations are common and interesting reactions. Typical procedures generally use electrochemical, photochemical, and ultrasonic techniques. Within the broad range of conditions for carrying out such reactions, the use of indium is of particular interest because it can be utilized in different solvents as organic media, water or without solvent. Besides, this metal is stable in air and its toxicity is lower compared with to that observed in other metals.1,2 In the context of contributing to the development of new synthetic methodology in the field of indium chemistry, as a preliminary study, we propose the use of ionic liquid as alternative solvent to carry out dehalogenation reactions. Dehalogenation of aromatics compounds was investigated by a series of reactions under several conditions. Bromobenzene was used as a starting material and due to ionic liquids (IL) have well-known properties as green solvents, we tested this procedure changing the IL.3,4 The treatment of bromobenzene with [bmim]Cl and [bmim]Br afforded the corresponding dehalogenated derivative in good to excellent yield. However, when using as an alternative others ionic liquids [bmim]PF6, [bmim]BF4, [bmpy]F3CSO3 and TBAF, reactions did not proceed. In order to ensure the validity of the results shown above for bromobenzene, we proceeded to extend this method for chlorinated and iodinated benzene. Our experimental results indicate that [bmim]Br is the most effective solvent for this reaction. To explore the scope of this dehalogenation reaction, we investigated the behavior of others haloaromatics and haloheteroaromatics systems using indium under [bmim]Br conditions. The yields of dehalogenated products were in moderate to excellent range. In conclusion, we have demonstrated that a reductive system consisting of an indium powder in ionic liquid allows a highly conversion of haloaromatics and haloheteroaromatics compounds. This work was supported by Bicentenario Project PSD-70, Interdisciplinary Project 27/2011, and Research Project 3901-026-81, Chemistry Faculty, Pontificia Universidad Católica de Chile. References 1 Alonso, F.; Beletskaya, I.; Yus, M. Chem. Rev. 2002, 102, 4009-4091. 2 Ranu, B. C.; Dutta, P.; Sarkar, A. J. Chem. Soc., Perkin Trans. I, 1999, 1139-1140. 3 Pavlinac, J.; Zupan, M.; Laali, K.; Stavber, S. Tetrahedron, 2009, 65, 5625-5662. 4 Sowmiah, S.; Srinivasadesikan, V.; Tseng, M-C.; Chu, Y-H. Molecules, 2009, 14, 3780-3813.

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