MRV

This review explores methods for optimizing emission wavelength, quantum yield and photostability of traditional and newer non-planar fluorophores (squaraine-rotaxanes and cycloparaphenylenes). We focus on the fundamental physical organic chemistry concepts leading to the fluorescent properties. We provide a detailed tutorial to understand fluorescence and enable the design of superior fluorophores for chemical biology.Social media promotion:

Abstract

Labeling and detection of biomolecules in vitro and in vivo is essential to many areas of biomedical science. Fluorophores stand as indispensable tools within chemical biology, underscoring the importance of fine-tuning their optical properties. This review focuses on methods for optimizing emission wavelength, quantum yield and photostability. We focus not just on the trends, but the fundamental physical organic chemistry concepts that inform the connection between molecular structure and fluorescent properties. This approach offers an essential understanding of fluorescence, enabling readers to develop a systematic analytical framework for thinking about fluorescence. Furthermore, an evaluation of newer non-planar fluorophores shines light on the bright future of fluorescent molecules.

An asymmetric nickel/metallaphotoredox catalyzed C(sp³)−H benzylic carbamoylation employing alkylarenes and isocyanates is described. A broad array of 2-arylamides can be prepared in one pot under mild reaction conditions. Mechanistic studies, including control experiments and DFT calculations, shed light on the rate and stereodetermining step of this transformation.

Abstract

Radical-mediated Hydrogen Atom Abstraction of Csp³−H bonds has become a powerful tool for the asymmetric functionalization of organic feedstocks. Here, we present an asymmetric synthesis of α-aryl amides via carbamoylation of alkylarenes with isocyanates as electrophiles. The synergistic combination of a photoredox and a chiral nickel-catalyst, enables the use of readily available and neutral reagents under mild reaction conditions and provides straightforward access to pharmacologically relevant motifs in enantiomerically pure form.

The first report on electrochemical Au^I/Au^III catalysis for 1,2-difunctionalization of C−C multiple bonds has been presented. This external-oxidant-free approach utilizes the anodic oxidation of vinyl-Au^I to vinyl-Au^III complexes to achieve oxy-alkynylation of allenoates to access alkyne-substituted butenolides in an undivided cell.

Abstract

Herein, we disclose the first report of 1,2-difunctionalization of C−C multiple bonds using electrochemical gold redox catalysis. By adopting the electrochemical strategy, the inherent π-activation and cross-coupling reactivity of gold catalysis are harnessed to develop the oxy-alkynylation of allenoates under external-oxidant-free conditions. Detailed mechanistic investigations such as ³¹P NMR, control experiments, mass studies, and cyclic voltammetric (CV) analysis have been performed to support the proposed reaction mechanism.

Electroreduction of benzylic olefins has been applied to site-selectively hydrogenate such double bonds while other functions that react under regular hydrogenation conditions are present. By the use of water as proton source this protocol also allows deuteration by simply switching to D₂O. The applicability of this method was shown by the use of a commercially available electrolysis setup and a broad substrate scope.

Abstract

We describe an operationally simple and user-friendly protocol that allows the site-selective hydrogenation and deuteration of di-, tri- and tetrasubstituted benzylic olefins by electroreduction while other groups prone to hydrogenation are present. The radical anionic intermediates react with the most inexpensive hydrogen/deuterium source H₂O/D₂O. Our method overcomes many limitations that arise from previously reported electroreductive hydrogenations. The applicability of this reaction is demonstrated by a broad substrate scope (>50 examples) that focuses on functional group tolerance and sites that are affected by metal-catalyzed hydrogenation (alkenes, alkynes, protecting groups).

Herein, we described a versatile photocatalytic strategy for the decarboxylative transformations of redox-active esters (RAE) to a variety of alkyl halides, amines, and olefins in the presence of ⁿBu₄NI in a single-step. It is a straightforward method which is applied to the functionalization of a series of primary, secondary, and tertiary aliphatic carboxylic acid derivatives and complex natural products. Mechanistically, a charge transfer complex (CTC) was formed through non-covalent interaction between RAE and ⁿBu₄NI. Upon photoexcitation, the ammonia salt acted as both an efficient electron donor and an iodine source for radical recombination. The mild reaction condition allows this method can be applied for modification of complex natural products and versatile follow-up transformations.

Abstract

Herein, we report an efficient photocatalytic strategy for the decarboxylative transformations of redox-active esters to construct C=C, C(sp³)−N, and C(sp³)−X bonds in a single-step. This operationally simple method provides a straightforward access to a variety of protected alkyl amines, alkyl halides and olefins under mild conditions in the absence of metals and photocatalysts. The method can successfully be applied to primary, secondary, and tertiary aliphatic carboxylic acid derivatives. Mechanistic studies indicate that the charge transfer complex (CTC) was formed by ⁿ Bu₄NI with redox-active esters, in which the ⁿ Bu₄NI acted as both an iodine source and an efficient electron donor.

Abstract

Isocyanides (isonitriles or carbylamine) have been intensively used in organic synthesis to prepare a diverse variety of N-heterocycles on the basis of the carbene-like reactivity of their divalent carbon atom. Isocyanides participate in a variety of reactions involving one, two, or more isocyanides. Compared to the popularity of single isocyanide reactions, few examples of reactions involving two or more isocyanides have been reported. In this review, we categorized and classified the literatures of reactions involving two or more isocyanides especially double isocyanide insertions under metal-catalyzed or metal-free conditions from 2014 to 2022.

Synthesis
DOI: 10.1055/a-2004-6485

Asymmetric catalysis is one of the most important areas of organic synthetic chemistry. In recent years, with the revival of organic electrochemistry, scientists have begun to try to combine asymmetric catalysis with electrochemistry to build valuable chiral molecules. In this review, we focus on examples of organic electrochemistry catalyzed by transition metals. According to the classification of the interaction of the catalyst with the substrate, we can divide them into two categories: (1) transition metal catalysts as chiral Lewis acids; (2) transition metal catalysts that construct chiral molecules by interacting with substrates through oxidative addition/reductive elimination.1 Introduction2 Electrochemical Asymmetric Lewis Acid Catalysis3 Electrochemical Asymmetric Transition Metal Catalysis4 Conclusion
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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A sustainable and efficient electrophotochemical metal-catalyzed protocol is developed for the direct conversion of readily available aliphatic carboxylic acids into chiral alkyl nitriles. Electrophotochemical Ce catalysis enables mild reaction conditions for radical decarboxylation to produce alkyl radicals, which could be effectively intercepted by asymmetric electrochemical Cu catalysis for the construction of C−CN bonds in a highly stereoselective manner.

Abstract

In contrast to the rapid growth of electrophotocatalysis in recent years, enantioselective catalytic reactions powered by this unique methodology remain rare. In this work, we report an electrophotochemical metal-catalyzed protocol for direct asymmetric decarboxylative cyanation of aliphatic carboxylic acids. The synergistic merging of electrophotochemical cerium catalysis and asymmetric electrochemical copper catalysis permits mild reaction conditions for the formation and utilization of the key carbon centered radicals by combining the power of light and electrical energy. Electrophotochemical cerium catalysis enables radical decarboxylation to produce alkyl radicals, which could be effectively intercepted by asymmetric electrochemical copper catalysis for the construction of C−CN bonds in a highly stereoselective fashion. This environmentally benign method smoothly converts a diverse array of arylacetic acids into the corresponding alkyl nitriles in good yields and enantioselectivities without using chemical oxidants or pre-functionalization of the acid substrates and can be readily scaled up.

Isocyanide-based Multicomponent Reactions in a new light! A review about challenges, potentialities, new trends, and future directions of exploiting isocyanide unique reactivity features under visible light irradiation.

Abstract

Isocyanide-based multicomponent reactions claim a one century-old history of flourishing developments. On the other hand, the enormous impact of recent progresses in visible light photocatalysis has boosted the identification of new straightforward and green approaches to both new and known chemical entities. In this context, the application of visible light photocatalytic conditions to multicomponent processes has been promoting key stimulating advancements. Spanning from radical-polar crossover pathways, to photoinduced and self-catalyzed transformations, to reactions involving the generation of imidoyl radical species, the present literature analysis would provide a general and critical overview about the potentialities and challenges of exploiting isocyanides in visible light photocatalytic multicomponent reactions.

Synthesis
DOI: 10.1055/a-1946-0512

Visible light photocatalysis has evolved into a promising mild and sustainable strategy to access radicals. This field unlocks formerly challenging or even previously inaccessible organic transformations. In this review, an overview of some lesser-known modes of photochemical activation of organic molecules and several emerging techniques within the versatile field of visible light photocatalysis are discussed. These are illustrated by selected photocatalytic reactions, with particular attention given to the reaction mechanism.1 Introduction2 Advanced Photoactivation Modes2.1 Photoinduced Hydrogen-Atom Transfer2.2 Proton-Coupled Electron Transfer2.3 Electron Donor-Acceptor Photoactivation of Organic Substrates2.4 Excited-State Transition Metal Catalysis3 Emerging Techniques3.1 Dual Catalysis3.2 Excited Radical Ion Photocatalysis3.3 Upconversion Strategies and Other Two-Photon Mechanisms3.4 Red and Near-Infrared Photocatalysis4 Conclusions and Outlook
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Article in Thieme eJournals:
Table of contents  |  Abstract  |  Full text