Polarography of heterocyclic aromatic compounds. XIII. Polarographic fission of carbon-halogen bonds in monohalogenopyridines
01 Jan 1962-Collection of Czechoslovak Chemical Communications (Institute of Organic Chemistry and Biochemistry AS CR, v.v.i.)-Vol. 27, Iss: 3, pp 680-692
About: This article is published in Collection of Czechoslovak Chemical Communications.The article was published on 1962-01-01. It has received 22 citations till now. The article focuses on the topics: Carbon & Polarography.
TL;DR: A review of the photochemical and electrochemical applications of multi-site proton-coupled electron transfer (MS-PCET) in organic synthesis can be found in this paper.
Abstract: We present here a review of the photochemical and electrochemical applications of multi-site proton-coupled electron transfer (MS-PCET) in organic synthesis. MS-PCETs are redox mechanisms in which both an electron and a proton are exchanged together, often in a concerted elementary step. As such, MS-PCET can function as a non-classical mechanism for homolytic bond activation, providing opportunities to generate synthetically useful free radical intermediates directly from a wide variety of common organic functional groups. We present an introduction to MS-PCET and a practitioner's guide to reaction design, with an emphasis on the unique energetic and selectivity features that are characteristic of this reaction class. We then present chapters on oxidative N-H, O-H, S-H, and C-H bond homolysis methods, for the generation of the corresponding neutral radical species. Then, chapters for reductive PCET activations involving carbonyl, imine, other X═Y π-systems, and heteroarenes, where neutral ketyl, α-amino, and heteroarene-derived radicals can be generated. Finally, we present chapters on the applications of MS-PCET in asymmetric catalysis and in materials and device applications. Within each chapter, we subdivide by the functional group undergoing homolysis, and thereafter by the type of transformation being promoted. Methods published prior to the end of December 2020 are presented.
TL;DR: The intermolecular alkylation of pyridine units with simple alkenes has been achieved via a photoredox radical mechanism, which is mild, tolerant of many functional groups, and effective for the preparation of a wide range of complex alkylpyridines.
Abstract: The intermolecular alkylation of pyridine units with simple alkenes has been achieved via a photoredox radical mechanism. This process occurs with complete regiocontrol, where single-electron reduction of halogenated pyridines regiospecifically yields the corresponding radicals in a programmed fashion, and radical addition to alkene substrates occurs with exclusive anti-Markovnikov selectivity. This system is mild, tolerant of many functional groups, and effective for the preparation of a wide range of complex alkylpyridines.
TL;DR: A combination of computational and experimental studies support a mechanism involving proton-coupled electron transfer followed by medium-dependent alkene addition and rapid hydrogen atom transfer mediated by a polarity-reversal catalyst.
Abstract: We report the photoredox alkylation of halopyridines using functionalized alkene and alkyne building blocks. Selective single-electron reduction of the halogenated pyridines provides the corresponding heteroaryl radicals, which undergo anti-Markovnikov addition to the alkene substrates. The system is shown to be mild and tolerant of a variety of alkene and alkyne subtypes. A combination of computational and experimental studies support a mechanism involving proton-coupled electron transfer followed by medium-dependent alkene addition and rapid hydrogen atom transfer mediated by a polarity-reversal catalyst.
TL;DR: A catalytic redox system for the direct conjugate addition of pyridines and diazines to Michael acceptors has been developed.
Abstract: The direct addition of pyridine and diazine units to electron-poor alkenes has been achieved via a redox radical mechanism that is enabled by limiting the effective concentration of the hydrogen-atom source. The described method is tolerant of acidic functional groups and is generally applicable to the union of a wide range of Michael acceptors and 6-membered heterocyclic halides.
TL;DR: A novel Ag/Cu alloy nanoparticles and graphene nanocomposite paste electrode was fabricated and its electrochemical activity was investigated using cyclic voltammetry and electrochemical impedance studies as mentioned in this paper.
Abstract: A novel Ag/Cu alloy nanoparticles and graphene nanocomposite paste electrode was fabricated and its electrochemical activity was investigated using cyclic voltammetry and electrochemical impedance studies. Electrochemical reduction of chlorpyrifos using the nanocomposite produced peak signal based on 2e − reductive cleavage of C Cl bond in trichloropyridine moiety. Increase in peak currents and decrease in overpotential for chlorpyrifos was observed for Ag/Cu–graphene nanocomposite compared to Ag–graphene, Cu–graphene, graphene paste and carbon paste electrodes. This could be attributed to the synergistic combination of graphene and Ag/Cu alloy nanoparticles with good adsorption, large surface area, increased active sites leading to fast electron transfer rates and high electrical conductivity of nanocomposite. A differential pulse adsorptive stripping voltammetric method was developed by using the above electrode for highly sensitive determination of chlorpyrifos under optimum instrumental and working conditions. A calibration plot of chlorpyrifos was studied over concentration range, 0.01–100 nM and detection limits of 4 × 10 −12 M were achieved. The method was successfully applied to well waters and soil samples and recovery values were in good agreement with HPLC–UV method.