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Incremental Introduction of Organocatalytic Activity into Conformationally Engineered Porphyrins
摘要： To study the correlation of macrocycle nonplanarity and catalytic activity of free base porphyrins in detail, a series of six tetraphenylporphyrins with graded degree of β-ethyl substitution ('H2EtxTPPs' 1–6; x = 0, 2, 4, 6, 8) was applied in organocatalyzed reactions. They display incrementally increasing nonplanarity due to repulsive peri-interactions. This creates an out-of-plane vector and better accessibility of the core amine and imine groups as the number of alkyl substituents increases. Following such a molecular engineering approach, the inner core system could be used to activate small molecules as a result of significant saddle distortion. The potential organocatalyst 'H2EtxTPPs' were used in benchmark sulfa-Michael reactions and we found a distinct relationship between nonplanarity and conversion. These observations were attributed to the combined effect of enhanced basicity and increased H-bonding potential that could facilitate bifunctional organocatalysis. Ultimately, density functional theory (DFT) calculations were performed on 1–6 to monitor some electronic properties of the title compounds.
关键词： porphyrins,organocatalysis,hydrogen bonds,molecular engineering,macrocycles
更新于2025-09-23 15:22:29
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RECENT APPLICATIONS IN ORGANIC SYNTHESIS OF VISIBLE LIGHT PHOTOREDOX CATALYSIS
摘要： RECENT APPLICATIONS IN ORGANIC SYNTHESIS OF VISIBLE LIGHT PHOTOREDOX CATALYSIS. In the past few years, photoredox catalysis has become a powerful tool in the field of organic synthesis. Using this efficient method, it is possible to excite organic compounds from visible light and attain alternative mechanistic pathways for the formation of chemical bonds, a result which is not obtainable by classical methods. The rapid growth of work in the area of photoredox catalysis is due to its low cost, broad chemical utility protocols, and, especially, its relevancy from the green and sustainable chemistry viewpoints. Thus, this study proposes a brief theoretical discussion of and highlights recent advances in visible-light-induced photoredox catalysis through the analysis of catalytic cycles and intermediates.
关键词： visible light,photoredox catalysis,organocatalysis,organic synthesis,transition metals
更新于2025-09-23 15:21:21
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When Does Organic Photoredox Catalysis Meet Artificial Photosynthesis?
摘要： The basics of photocatalysis are under investigation for more than a century. Contemporary science maintains an emphasis on fundamental studies, but application-oriented research in solar energy conversion, environmental remediation, light-promoted chemical synthesis and medicinal phototherapy is growing rapidly. These prospects have triggered a renaissance of the field and breath-taking progress has been made in the last decade by chemists from all major branches. Artificial photosynthesis aims to produce a renewable fuel using sunlight. This 'solar fuel' is thereby synthesized from the reduction of water or carbon dioxide, coupled to the oxidation of a substrate; typically, water to O2. The underlying endothermic multi-electron/multi-proton chemistry is relatively well understood, but the assembly of a commercially viable device remains elusive due to the 'low' market-value of chemical fuels. Photoreforming can decompose organics such as waste biomass (lignocellulose), plastics or pollutants to produce a fuel using solar irradiation. This process has overall a much-reduced thermodynamic barrier compared to overall water splitting, but suffers from a kinetically challenging reaction, insufficient solubility of polymeric substrate or low concentration of pollutants. Organic photoredox catalysis uses light to accelerate chemical reactions by well-controlled single-electron redox events. This radical chemistry approach has not only allowed for improved synthetic procedures, but also new transformations to proceed. The value-added organic products are synthesized in controlled laboratory environments, usually using LED lamps. Although photocatalysis is of growing interest to the chemical and pharmaceutical industry, large-scale processes have rarely been implemented. Medicinal chemistry develops light sensitive medication for the destruction of abnormal cells. In photodynamic therapy, the photosensitizer drug is irradiated using a defined wavelength and reacts with O2 to produce reactive oxygen species to exert phototoxicity. Achieving high quantum yields and the development of red (or near IR) light absorbers (for improved skin penetration) are common objectives with artificial photosynthesis (for optimal solar light harvesting). Although the same basics of photochemistry unite these applications, they are being developed in surprising isolation as inorganic and physical chemists focus on artificial photosynthesis, chemical engineers on photoreformation, organic chemists on photoredox catalysis, and medicinal chemists on photodynamic therapy. This divide is cemented by separating the scientists often in different institutes, teaching structures and firmly placing them in separate academic communities. This editorial is intended as a call to join forces and embrace progress in all of these areas to enable accelerated development of a more holistic science in photocatalysis. There is plenty we can learn from each other as we share mutual interests and common goals. The quickly developing pool of environmentally benign, robust, non-toxic, scalable and efficient photocatalysts for solar fuel synthesis provides vast opportunities for improved and new organic catalysis. For example, heterogeneous photocatalysts such as semiconductor powders and photoelectrochemical architectures are rarely employed in organic chemistry. Time-resolved spectroscopy can provide in-depth understanding of electron transfer dynamics and insights into organic mechanisms. Proton-coupled multi-electron and endothermic photochemistry may pave the way to currently inaccessible organic chemistry. Coupling of solar fuel synthesis to value added oxidation chemistry for bulk or even fine chemical synthesis is a largely untapped territory (Figure 1). The simultaneous production of a chemical fuel and value-added organic improves the economics in artificial photosynthesis and may accelerate market penetration for solar fuels. Understanding organic transformations and industrial processes allows the selection of meaningful alternatives to water oxidation. Clean organic oxidations with high selectivity and conversion yield are key criteria to distinguish them from the use of undesirable sacrificial electron donors. It may be true that we cannot produce enough fuel to power the planet by coupling fuel synthesis to organic chemistry, but it is nevertheless an attractive entry point for commercialisation as well as a rich intellectual playground for academic research. Photoreforming can be exploited for simultaneous fuel production and chemical synthesis from an organic waste substrate, thereby addressing the issues of renewable energy generation and sustainable chemical synthesis with environmental remediation. Agricultural and plastic waste are a valuable resource that should not go to landfills. It contains stored energy and useful chemical building blocks for chemical transformations. Photoreformation of lignocellulose and plastics has been demonstrated to provide access to clean H2 fuel as well as organic chemicals. A final question concerns the use of sunlight versus electrical (LED) irradiation and this will ultimately depend on the application. The common view is that the synthesis of organics will be performed in the laboratory using LEDs, whereas fuel production requires large land-areas and therefore sunlight. But there are plenty of alternative possibilities and scenarios to challenge this traditional view. Could the drop in renewable (solar) electricity production may ultimately make fuel synthesis with efficient LEDs possible? Why not consider swimming-pool sized flow-reactors powered by the sun for bulk chemical production or solar-concentrators for greener organic synthesis? Solar-driven chemistry can also give access to off-grid synthesis of fertilisers, medicine, and commodities in remote areas and sun-rich developing countries. Some of these suggestions may indeed appear naive, but cross-fertilisation and an open mind will ultimately provide the basis for new developments in photocatalysis.
关键词： photocatalysis,photosynthesis,organocatalysis,solar fuels,redox chemistry
更新于2025-09-19 17:15:36
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Photo‐Organocatalytic Enantioselective Radical Cascade Enabled by Single‐Electron Transfer Activation of Allenes
摘要： Allenes are commonly used in metal-mediated transformations, cycloaddition reactions, and radical processes. However, their activation by single-electron transfer (SET) is largely underexplored. Herein, we report a visible light-driven enantioselective organocatalytic process that uses the excited-state reactivity of chiral iminium ions to activate allenes by SET oxidation. The ensuing allene cation radicals participate in stereocontrolled cascade reactions to deliver bicyclic scaffolds with good enantioselectivity and exquisite diastereoselectivity. Density Functional Theory (DFT) calculations support a mechanism that combines the peculiar chemistry of allene radical cations with polar reactivity.
关键词： photochemistry,cascade process,allene,enantioselective organocatalysis,radical chemistry
更新于2025-09-19 17:13:59
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Synthesis and Application of Substituted-1,16-dihydroxytetraphenylenes in Catalytic Asymmetric Allylboration of Ketones
摘要： The synthesis and application of a newly designed C2-symmetric chiral substituted-1,16-dihedroxytetraphenylenes (DHTP) is reported. Efficient syntheses of enantiopure substituted-DHTP were accomplished, and these enantiopure compounds were used as organocatalysts in asymmetric allylboration of ketones under very mild conditions. Accordingly, several tertiary alcohols were generated in moderate to good yields with up to 99% ee by using the catalyst (S)-2,15-Br2-DHTP. A gram-scale reaction was achieved in 99% yield with 96% ee.
关键词： 16-dihedroxytetraphenylenes,asymmetric allylboration,ketones,chiral catalysts,organocatalysis,substituted-1
更新于2025-09-04 15:30:14