Robby Vroemans

Nature Reviews Chemistry, Published online: 18 February 2021; doi:10.1038/s41570-021-00255-8

The Cover Feature shows a chiral sulfinyl auxiliary in the ortho‐position of a biaryl axis inducing a C–H activated atroposelective macrocyclization with final transformation to the configurationally stable natural Isoriccardin C. More information can be found in the Communication by S. Choppin, A. Speicher et al.

Nature Communications, Published online: 23 February 2021; doi:10.1038/s41467-021-21726-y

Synthesis
DOI: 10.1055/s-0040-1706023

(4+3)-Annulations are incredibly versatile reactions which combine a 4-atom synthon and a 3-atom synthon to form both 7-membered carbocycles as well as heterocycles. We have previously reviewed transition-metal-catalyzed (4+3)-annulations. In this review, we will cover examples involving bases, NHCs, phosphines, Lewis and Brønsted acids as well as some rare examples of boronic acid catalysis and photocatalysis. In analogy to our previous review, we exclude annulations involving cyclic dienes like furan, pyrrole, cyclohexadiene or cyclopentadiene, as Chiu, Harmata, Fernándes and others have recently published reviews encompassing such substrates. We will however discuss the recent additions (2010–2020) to the literature on (4+3)-annulations involving other types of 4-atom-synthons.1 Introduction2 Bases3 Annulations Using N-Heterocyclic Carbenes3.1 N-Heterocyclic Carbenes (NHCs)3.2 N-Heterocyclic Carbenes and Base Dual-Activation4 Phosphines5 Acids5.1 Lewis Acids5.2 Brønsted Acids6 Boronic Acid Catalysis and Photocatalysis7 Conclusion
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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

The enantioselective addition of aryllithiums onto arynes, leading to axially chiral biaryls in the absence of transition metals, was investigated by means of chiral ligands of lithium. Biaryls with a high degree of steric congestion around the aryl–aryl bond could be obtained.

Abstract

For the first time, the challenging atropo‐enantioselective coupling of in‐situ generated arynes and aryllithiums in the presence of a chiral ligand of lithium was investigated. This preliminary study demonstrates the feasibility of this concept, by affording enantioenriched axially chiral biaryls even in the case of products showing a high degree of steric congestion around the newly created aryl−aryl bond.

A phthalocyanine chromophore absorbing in the far-red region with a tyrosine residue hydrogen bonded to an imidazole moiety provides the first example of a bioinspired model for the recent discovery that chlorophyll f-containing Photosystem II absorbing in the far-red limit at 727 nm can drive the four-electron water oxidation.

Abstract

The textbook explanation that P₆₈₀ pigments are the red limit to drive oxygenic photosynthesis must be reconsidered by the recent discovery that chlorophyll f (Chlf)-containing Photosystem II (PSII) absorbing at 727 nm can drive water oxidation. Two different families of unsymmetrically substituted Zn phthalocyanines (Pc) absorbing in the 700–800 nm spectral window and containing a fused imidazole-phenyl substituent or a fused imidazole-hydroxyphenyl group have been synthetized and characterized as a bioinspired model of the Chlf/Tyrosine_Z/Histidine₁₉₀ cofactors of PSII. Transient absorption studies in the presence of an electron acceptor and irradiating in the far-red region evidenced an intramolecular electron transfer process. Visible and FT-IR signatures indicate the formation of a hydrogen-bonded phenoxyl radical in ZnPc II-OH. This study sets the foundation for the utilization of a broader spectral window for multi-electronic catalytic processes with one of the most robust and efficient dyes.

All smiles: This review summarizes recent reports on photoinduced aryl migration reactions to allow the access to a broad range of functionalized structures. These transformations occur by remote rearrangements and functional‐group modifications. The use of such a strategy opens the way to a plethora of structures under mild and efficient conditions.

Abstract

Rearrangement reactions are certainly one of the most useful approaches towards complex structures in organic chemistry. With efficient conditions, it is indeed possible to convert simple substrates into highly functionalized products. Moreover, combining this approach with an attractive initiation process, such as visible‐light catalysis, makes these reactions particularly powerful. Recently, tremendous improvements have been made, owing to a better understanding of photoredox mechanisms. In this review, recent progress on visible‐light aryl migration reactions is discussed, focusing especially on Smiles rearrangement and related reactions.

A SO₂ surrogate (SOgen) is reported, which is cheap, bench‐stable, and accessible in just two steps from bulk chemicals. SOgen releases SO₂ in just a few minutes when heated in the presence of a styrene. The compatibility of this gas‐releasing method with eight previously reported sulfonylation reactions was demonstrated in a two‐chamber system. Direct aminosulfonylation between aryl iodides and amines is reported.

Abstract

A new SO₂ surrogate is reported that is cheap, bench‐stable, and can be accessed in just two steps from bulk chemicals. Essentially complete SO₂ release is achieved in 5 minutes. Eight established sulfonylation reactions proceeded smoothly by ex situ formation of SO₂ by utilizing a two‐chamber system in combination with the SO₂ surrogate. Furthermore, we report the first direct aminosulfonylation between aryl iodides and amines. Broad functional group tolerance is demonstrated, and the method is applicable to pharmaceutically relevant substrates, including heterocyclic substrates.

Abstract

The rhodium-catalyzed transannulation of N-perfluoroalkyl-1,2,3-triazoles with aromatic and aliphatic terminal alkynes under microwave heating conditions afforded N-perfluoroalkyl-3,4-disubstituted pyrroles (major products) and N-fluoroalkyl-2,4-disubstituted pyrroles (minor products). The observed selectivities in the case of the reactions with aliphatic alkynes were high.

Beilstein J. Org. Chem. 2021, 17, 504–510. doi:10.3762/bjoc.17.44

A radically new approach to the synthesis of 1‐(dialkylamino)‐1,2,3‐triazoles via addition of diazomethyl radicals to hydrazones is described. This reactivity confirms the utility of the α‐diazosulfonium salts herein introduced as synthetic equivalents of the diazomethyl cation.

Abstract

The one‐pot synthesis of a series of sulfonium salts containing transferable diazomethyl groups is described, and the structure of these compounds is elucidated by X‐ray crystallography. Under photochemical conditions, reaction of these salts with N,N‐dialkyl hydrazones affords 1‐(dialkylamino)‐1,2,3‐triazoles via diazomethyl radical addition to the azomethine carbon followed by intramolecular ring closure. The straightforward transformation of the structures thus obtained into mesoionic carbene–metal complexes is also reported and the donor properties of these new ligands characterized.

Abstract

A metal- and additive-free, highly efficient, step-economical deoxygenative C2-heteroarylation of quinolines and isoquinolines was achieved from readily available N-oxides and N-sulfonyl-1,2,3-triazoles. A variety of α-triazolylquinoline derivatives were synthesized with good regioselectivity and in excellent yields under mild reaction conditions. Further, a gram-scale and one-pot synthesis illustrated the efficacy and simplicity of the developed protocol. The current transformation was also found to be compatible for the late-stage modification of natural products.

Beilstein J. Org. Chem. 2021, 17, 485–493. doi:10.3762/bjoc.17.42

Synlett
DOI: 10.1055/s-0040-1706681

Phosphonylation of alkenes is important for the generation of valuable organophosphines. However, redox-neutral difunctionalization of alkenes with readily available H-P(O) compounds remains underdeveloped. Herein, we report the first visible-light-driven redox-neutral phosphonoalkylation of alkenes. A variety of organophosphorus-containing three-membered carbocyclic scaffolds are synthesized from alkene-bearing alkyl sulfonates with H-P(O) compounds. The transition-metal-free protocol displays good functional group tolerance, broad substrate scope, high yields, and mild reaction conditions.
[...]

Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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

Abstract

Phosphonodepsipeptides are phosphorus analogues of depsipeptides and phosphonate-linked analogues of naturally occurring peptides. They are more stable than phosphonopeptides and have been widely applied as enzyme inhibitors, haptens for the production of antibodies, biological agents, and prodrugs. The synthetic strategies towards phosphonodepsipeptides are reviewed, including the phosphonylation of hydroxy esters with phosphonochloridates, the condensation of phosphonic monoesters and hydroxy esters, the alkylation of phosphonic monoesters with 1-(alkoxycarbonyl)alkyl halides or sulfonates, multicomponent condensation of amides, aldehydes, and dichlorophosphites followed by alcoholysis with hydroxy esters, the phosphinylation of hydroxy esters with phosphonochloridites followed by oxidation, and the carbene insertion of N-protected amino acids with 1-diazoalkylphosphonates. This review includes the synthesis of α-, β-, and γ-phosphonodepsipeptides and phosphonodepsipeptides with C-1-hydroxyalkylphosphonic acids.

Beilstein J. Org. Chem. 2021, 17, 461–484. doi:10.3762/bjoc.17.41

This Minireview describes the use of 1,2,3‐triazole and triazolium groups, as well as their halogenated and chalcogenated derivatives, for anion templated self‐assembly. Recent advances in the areas of foldamers, supramolecular polymers and interlocked structures are described including the use of these architectures for anion recognition and catalysis applications.

Abstract

The use of 1,2,3‐triazole and triazolium motifs to construct anion templated supramolecular structures has grown rapidly over the past decade and has enabled a range of complex structures to be synthesised. In this Minireview we highlight the significant advances that have been made in areas such as foldamers, polymers and interlocked systems.

Abstract

A new approach was designed for the synthesis of C6-substituted 2-triazolylpurine derivatives. A series of substituted products was obtained in S_NAr reactions between 2,6-bistriazolylpurine derivatives and O- and C-nucleophiles under mild conditions. The products were isolated in yields up to 87%. The developed C–O and C–C bond forming reactions clearly show the ability of the 1,2,3-triazolyl ring at the C6 position of purine to act as leaving group.

Beilstein J. Org. Chem. 2021, 17, 410–419. doi:10.3762/bjoc.17.37