MarjoW

Nature, Published online: 24 August 2022; doi:10.1038/d41586-022-02213-w

Synthesis
DOI: 10.1055/a-1892-5473

Enamides, as prefunctionalized electron-rich heteroatom-substituted alkenes represent a powerful platform to synthesize useful nitrogen-containing natural products and bioactive molecules. This review discloses recent progress in the transition-metal-catalyzed enantioselective functionalization of enamides, including the Heck reaction, hydrofunctionalization, and difunctionalization, with a focus on the general scope, current limitations, stereochemical reaction control, and mechanistic aspects.1 Introduction2 Asymmetric Heck Reaction of Enamides3 Asymmetric Hydrofunctionalization of Enamides3.1 Nickel Catalysis3.2 Copper Catalysis3.3 Rhodium Catalysis3.4 Iridium Catalysis4 Asymmetric Difunctionalization of Enamides4.1 Palladium Catalysis4.2 Nickel Catalysis4.3 Copper Catalysis5 Summary and Outlook
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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Publication date: 13 October 2022

Source: Chem, Volume 8, Issue 10

Author(s): Xianhong Wu, Yi Wang, Zhong-Shuai Wu

Nature, Published online: 22 August 2022; doi:10.1038/d41586-022-02297-4

Photocatalysis: The population of ligand-to-metal charge-transfer (LMCT) excited states upon light irradiation of abundant and inexpensive 3d-metal complexes represents an effective platform to access open-shell intermediates of high synthetic value. This review provides guidelines for the utilization of this inner-sphere reactivity, a comparison of its distinct profile in comparison with photoredox catalysis, and a collection of the most relevant achievements applied to organic synthesis.

Abstract

Despite the rich photochemistry of 3d-metal complexes, the utilization of excited-state reactivity of these compounds in organic synthesis has been historically overlooked. The advent of photoredox catalysis has changed the perception of synthetic chemists towards photochemistry, and nowadays the potential of photoinduced, outer-sphere single-electron transfer events is widely recognized. More recently, an emerging new mode of photoactivation has taken the spotlight, based on an inner-sphere mode of reactivity triggered by population of ligand-to-metal charge-transfer (LMCT) excited states. Contrarily to photoredox, LMCT-activation does not rely on matching redox potentials, offers unique reactivity profiles and is particularly well suited on Earth-abundant metal complexes. Those appealing features are propelling the development of methods using this blueprint to generate highly reactive open-shell species under mild conditions. The aim of this contribution is to provide a didactical tool for the comprehension of this emerging concept and facilitate the development of new synthetic methodologies to achieve sustainable chemical transformations.

In this mini-review, we have presented the recent progress in dual palladium – photoredox catalyzed C−H functionalization reactions such as C−H arylation, acylation, olefination & hetero atom functionalization.

Abstract

Functionalization of unactivated C−H bonds is a highly desirable process in organic chemistry as it gives direct access to new functional groups in a single step. This process is generally achieved using transition metal catalysts, and among them, palladium plays an important role due to its unique reactivity. Recently, photoredox catalysis has witnessed a huge surge, and many new and valuable organic reactions are uncovered periodically. Dual transition metal – photoredox catalysis on the other hand, has taken organic synthesis to new heights by achieving transformations that were previously not possible or difficult to achieve by both forms of catalysis independently. In this direction, many new and interesting dual palladium-photoredox catalyzed C−H functionalization reactions combining the synergistic effects of both palladium and photoredox have been reported in the past few years, and it is imperative to summarize these reactions for further developments in this area.

Publication date: Available online 27 June 2022

Source: Chem

Author(s): Qilei Zhu, Daniel G. Nocera

Abstract

Olefins are important building blocks and are widely utilized in synthetic organic chemistry. Owing to its omnipresence and unique reactivity, the functionalization of alkenes has become a powerful method for constructing complex organic molecules. In this context, direct chelation-assisted C−H olefination at the inert C−H bonds represents the most straightforward synthetic method for introducing the alkenyl group into organic compounds in a highly regio- and stereoselective manner. Despite the remarkable advances in chelation-assisted C−H olefination reaction, most of the successful transformations are restricted to activated or electronically biased olefins such as acrylates, styrenes, acrylamides, vinyl sulfones, and vinyl phosphonates. Literature reports on chelation-assisted C−H olefination with unactivated or electronically unbiased alkenes are limited due to poor intrinsic reactivity and regioselectivity issues. Despite significant challenges, the past few years have witnessed tremendous growth. The present review describes the recent advances in the chelation-assisted C−H olefination and allylation of aromatics, alkenes, and heteroaromatics with unactivated alkenes via the concerted-metallation- deprotonation pathway.Transition metals such as palladium, rhodium, iridium and cobalt are widely used for these kind of transformations. The scope, mechanistic investigation, and limitation of the alkenylation and allylation reactions are discussed elaborately. The present review includes all the reported C−H olefination and allylation reactions with unactivated olefins via the base-assisted deprotonation pathway.

A new electrophilic/nucleophilic dithiocyanation of alkynes with N-thiocyanato-dibenzenesulfonimide (NTSI) and NH₄SCN has been demonstrated. The protocol features a broad substrate scope, mild reaction condition, and high yields.

Abstract

Organic thiocyanates widely exist in natural products, and act as important precursors for organic synthesis. An efficient dithiocyanation of alkynes with N-thiocyanato-dibenzenesulfonimide (NTSI) as the SCN⁺ cation and ammonium thiocyanate as the SCN^- anion sources has been developed. Highly active electrophilic reagent NTSI could react with various types of alkynes to build C(sp²)−SCN bond to provide a variety of dithiocyanato olefin compounds under simple and mild conditions. Trace amount of water is beneficial to the dissociation of ammonium thiocyanate, which makes the SCN^- anion easier to participate in the reaction. The protocol owns a broad substrates scope including terminal and internal, alkyl and aryl alkynes, excellent functional group tolerance and good regioselectivity.

Synthesis
DOI: 10.1055/a-1776-0929

The synthesis of a set of new organic photocatalysts (PCs) with a donor-acceptor carbazolyl dicyanobenzene structure is reported. The PCs developed have fine-tailored redox potentials from –1.62 V (PC•+/PC*) to 1.36 V (PC*/PC•–) and were accessed through a straightforward two-step synthesis. The potential of these PCs was demonstrated in synthetically relevant reactions with mechanistically opposite thermodynamic requirements, previously reported only in the presence of precious Ir-based PCs. In addition, the PCs outperformed the yields promoted by the well-established 4CzIPN organic dye in both type of reactions.
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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