MRV

Synlett
DOI: 10.1055/a-2225-8858

We report the photocatalytic functionalization of terminal alkenes to vicinal dichlorides by using visible light and FeCl3 as a catalyst, LiCl as a chloride source, and air as an oxidant. The transformation is proposed to be initiated by ligand-to-metal charge-transfer bond homolysis of a Fe–Cl bond, giving a highly reactive chloride radical able to initiate the functionalization of olefins. The process shows high chemoselectivity and broad functional-group tolerance with yields of up to 94% under mild conditions.
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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

Shaping Chirality from Heterocyles. The mild, organocatalytic generation of elusive ortho-quinodimethane intermediates (Het-oQDMs) from suitable heteroaromatic carbonyl- or carbonyl-like pronucleophiles has recently proved to be succesful in the development of enantioselective [4+2] cycloadditions, giving access to novel, chiral heterocyclic chemotypes featuring in-cycle stereocenters. This review provides a critical analysis of the most important advances in the field achieved in the last decade.

Abstract

Polycyclic compounds bearing a complex heterocyclic core such as an aromatic heterocycle “fused” with one or more functionalized rings, are widespread leading molecules in the domain of synthetic organic chemistry and pharmaceuticals. Although many synthetic methodologies have been devised to access achiral, fused heteroaromatic scaffolds, or related chiral variants adorned with out-of-cycle stereogenic elements, equally efficient strategies to afford chiral heterocycles featuring in-cycle stereocenters, exist to a lesser extent and presently represent a growing field of investigation. The mild, organocatalytic generation of elusive ortho-quinodimethane intermediates (oQDMs), derived from suitable heteroaromatic carbonyl- or carbonyl-like pronucleophiles has recently proved successful in the synthesis of such peculiar chiral architectures via stereoselective [4+2] cycloadditions. This review provides an overview of the most important advances attained in this field over the last decade.

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.