LongLarf

Versatile and robust C–C activation by chelation-assisted manganese catalysis

Versatile and robust C–C activation by chelation-assisted manganese catalysis, Published online: 10 December 2018; doi:10.1038/s41929-018-0187-1

Unlike the more common C–H functionalization, methods for the functionalization of C–C bonds are scarce. Here, Ackermann and co-workers show that an inexpensive manganese catalyst is capable of selectively activating C–C bonds for alkylations, alkenylations, and allylations in water.

Abstract

This review aims to report recent advances on decarboxylative reactions of amino acids catalyzed by transition metals or non‐metals and the growing opportunities they present in the construction of complex chemical scaffolds for applications encompassing natural product synthesis, synthetic methodology development, and functional materials. Different decarboxylative reactions have been highlighted such as radical, photoredox and metal and metal‐free coupling reactions. etc. The review is divided into two main sections: one deals with reactions via radical pathways and the other via azomethine ylide pathways. The reactions have been discussed in more detail with particular emphasis on their useful applications and mechanistic illustrations.

Abbreviations: 1,3‐DCB: 1,3‐dicyanobenzene; 1,4‐DCB: 1,4‐dicyanobenzene; Acr: acridinium; BI: benziodoxolone; Boc: tert‐butoxycarbonyl; CB: conduction band; CBX: cyanobenziodoxolone; CFL: compact fluorescent lamp; DBU: 1,8‐diazabicyclo[5.4.0]undec‐7‐ene; DCA: 9,10‐dicyanoanthracene; DCB: 1,2‐dichlorobenzene; DCE: 1,2‐dichloroethane; DDDS: bis(4‐chlorophenyl) disulfide; DIPEA: diisopropylethylamine; DMA: N,N‐dimethylacetamide; DMF: N,N‐dimethylformamide; DMSO: dimethyl sulfoxide; DNA: deoxyribonucleic acid; dtbbpy: 4,4′‐di‐tert‐butyl‐2,2'‐bipyridine; DTBP: di‐tert‐butyl peroxide; equiv.: equivalent; ET: electron transfer; h: hour; HE: Hantzsch ester; LED: light‐emitting diode; min: minutes; mL: millilitre; MS: molecular sieves; MW: microwave; nm: nanometer; NS: nanosphere; Nu: nucleophile; ODCB: o‐dichlorobenzene; PA‐1: (±)‐1,1′‐binaphthyl‐2,2′‐diyl hydrogen phosphate; PC: photocatalyst; PET: photoinduced electron transfer; PEG: polyethylene glycol; PG: protecting group; Phen: phenanthrene; PTA: phosphotungstic acid 44‐hydrate; RNA: ribonucleic acid; r.t.: room temperature; SET: single‐electron transfer; TBAI: tetrabutylammonium iodide; TBHP: tert‐butyl hydroperoxide; TFA: trifluoroacetic acid; THF: tetrahydrofuran; TMEDA: N,N,N′,N′‐tetramethylethylenediamine; TS: transition state; UV: ultraviolet; VB: valence band; W: watt.

Why a postdoc might not advance your career

Why a postdoc might not advance your career, Published online: 07 December 2018; doi:10.1038/d41586-018-07652-y

Two studies reiterate that very few postdoctoral researchers land academic posts — and suggest that the skills postdocs learn are not sought by employers outside academia.

Just add salt! Water with added NaCl was a very effective reaction medium for performing direct and fast (within 20 s) Pd‐catalysed cross‐coupling reactions between organolithiums and a variety of (hetero)aryl halides at room temperature and under air. Catalyst and water recyclability and reusability were added advantages of the proposed protocol.

Abstract

Direct palladium‐catalysed cross‐couplings between organolithium reagents and (hetero)aryl halides (Br, Cl) proceed fast, cleanly and selectively at room temperature in air, with water as the only reaction medium and in the presence of NaCl as a cheap additive. Under optimised reaction conditions, a water‐accelerated catalysis is responsible for furnishing C(sp³)–C(sp²), C(sp²)–C(sp²), and C(sp)–C(sp²) cross‐coupled products, in competition with protonolysis, within a reaction time of 20 s, in yields of up to 99 %, and in the absence of undesired dehalogenated/homocoupling side products even when challenging secondary organolithiums serve as the starting material. It is worth noting that the proposed protocol is scalable and the catalyst and water can easily and successfully be recycled up to 10 times, with an E‐factor as low as 7.35.

Just diene to be arylated: A strategy was developed for the chemoselective hydroarylation of 1,3‐dienes with phenols through a borane‐promoted protonation/Friedel–Crafts‐type mechanism (see scheme). The transformation showed good functional‐group compatibility for the efficient synthesis of diverse ortho‐allyl phenols.

Abstract

A B(C₆F₅)₃‐catalyzed hydroarylation of a series of 1,3‐dienes with various phenols has been established through a combination of theoretical and experimental investigations, affording structurally diverse ortho‐allyl phenols. DFT calculations show that the reaction proceeds through a borane‐promoted protonation/Friedel–Crafts pathway involving a π‐complex of a carbocation–anion contact ion pair. This protocol features simple and mild reaction conditions, broad functional‐group tolerance, and low catalyst loading. The obtained ortho‐allyl phenols could be further converted into flavan derivatives using B(C₆F₅)₃ with good cis diastereoselectivity. Furthermore, this transformation was applied in the late‐stage modification of pharmaceutical compounds.

Photochemical generation of radicals from alkyl electrophiles using a nucleophilic organic catalyst

Photochemical generation of radicals from alkyl electrophiles using a nucleophilic organic catalyst, Published online: 03 December 2018; doi:10.1038/s41557-018-0173-x

The SN2 reaction, a fundamental process associated with ionic chemistry, can be incorporated into a photochemical approach to creating radicals from alkyl electrophiles. This method occurs readily under visible-light irradiation, exhibits broad functional-group tolerance, and enables the formation of open-shell intermediates from substrates that are incompatible with traditional radical-generating strategies.

Modern applications of low-valent early transition metals in synthesis and catalysis

Modern applications of low-valent early transition metals in synthesis and catalysis, Published online: 30 November 2018; doi:10.1038/s41570-018-0059-x

Low-valent early transition metals are experiencing a renaissance in synthesis and catalysis, finding applications in unusual C–C bond forming reactions, oxidative group-transfer catalysis, proton-coupled electron transfer, photoredox catalysis and more.

Even plastic can be reduced! Transfer hydrogenation of esters and lactones with EtOH can be effected using 5 mol % of Fe‐MACHO‐BH as catalyst. This catalyst does not need any base activation, thus resulting in very high selectivities.

Abstract

Herein, we report on the use of the iron pincer complex Iron‐MACHO‐BH, in the base‐free transfer hydrogenation of esters with EtOH as a hydrogen source. More than 20 substrates including aromatic and aliphatic esters and lactones were reduced affording the desired primary alcohols and diols with moderate to excellent isolated yields. It is also possible to reduce polyesters to the diols with this method, enabling a novel way of plastic recycling. Reduction of the renewable substrate methyl levulinate proceeds to form 1,4‐pentanediol directly. The yields are largely governed by the equilibrium between the alcohol and the ethyl ester.

Abstract

The use of carbon dioxide (CO ₂ ) as a building block in organic synthesis is a topic of high interest. We here reflect from an industrial perspective, which of the approaches may have the potential to be applied in the near future in industrial organic synthesis on a significant scale. Drawbacks to overcome and challenges to be addressed are also discussed in this critical review. This review focuses on systems providing a high atom‐efficiency and which could be competitive to other state‐of‐the art syntheses.

Photocarboxylation: Visible‐light‐promoted metal‐free difunctionalization of alkenes using CO₂ and readily available Si−H and C(sp³)−H reagents has been realized by the merging of photoredox and hydrogen‐atom‐transfer catalysis. A variety of valuable compounds, such as β‐silacarboxylic acids and acids bearing a γ‐heteroatom (e.g., N, O, S) can be directly accessed from simple alkenes in a redox‐neutral fashion.

Abstract

Catalytic alkene difunctionalization via Si−H and C−H activations represents an ideal atom‐ and step‐economic pathway for quick assembly of molecular complexity. We herein developed a visible‐light‐promoted metal‐free difunctionalization of alkenes using abundant CO₂ and readily available Si−H and C(sp³)−H bonds as feedstocks. Through the merger of photoredox and hydrogen‐atom‐transfer catalysis, a variety of value‐added compounds, such as β‐silacarboxylic acids and acids bearing a γ‐heteroatom (e.g., N, O, S) could be directly accessed from simple alkenes in a redox‐neutral fashion.