Sebastian Beil

Nature Communications, Published online: 06 February 2020; doi:10.1038/s41467-020-14322-z

While electrosynthesis represents a green and advantageous alternative to traditional synthetic methods, electrochemical reactions still suffer from some drawbacks that require further efforts in order to fully express the potential of electricity-driven transformations. In this Comment, we will briefly discuss both the advantages and limitations of electrosynthesis, especially when compared with the other traditional synthetic organic methods, and share some forward-looking thoughts on the future developments of electrochemical reactions.

Nature, Published online: 06 February 2020; doi:10.1038/d41586-020-00335-7

Investigation finds that biophysicist Kuo-Chen Chou repeatedly suggested dozens of citations be added to papers.

Canataxpropellane belongs to the medicinally important taxane diterpene family. The most prominent congener, Taxol, is one of the most commonly used anticancer agent in clinics today. Canataxpropellane exhibits a taxane skeleton with three additional transannular C–C bonds, resulting in a total of six contiguous quaternary carbons, of which four are located on a cyclobutane ring. Unfortunately, isolation of canataxpropellane from natural sources is inefficient. Here, we report a total synthesis of (–)-canataxpropellane in 26 steps and 0.5% overall yield from a known intermediate corresponding to 29 steps from commercial material. The core structure of the (–)-canataxpropellane (2) was assembled in two steps using a Diels–Alder/ortho-alkene-arene photocycloaddition sequence. Enantioselectivity was introduced by designing chiral siloxanes to serve as auxiliaries in the Diels–Alder reaction.

All systems go : Increased research on large molecules will reveal construction principles dictated by recurring motifs that govern structure formation through folding and self‐assembly. These principles are comparable to the organization of atoms in the Periodic Table of Chemical Elements and could lead to the establishment of a Periodic System of Supramolecular Elements.

Abstract

Chemistry “beyond the molecule” is based on weak, noncovalent, and reversible interactions. As a consequence of these bonds being weak, structural organization by folding and self‐assembly can only be fully exploited with larger molecules that can provide multiple binding sites. Such “supramolecules” can now be synthesized and their folding into desired conformations predicted. A new level of chemistry can now be realized through the creation of non‐natural entities composed of molecular building blocks with defined secondary structures. Herein we define these building blocks as “supramolecular elements”. We anticipate that further research on such large molecules will reveal construction principles dictated by recurring motifs that govern structure formation through folding and self‐assembly. These principles are comparable to the organization of atoms in the Periodic Table of Chemical Elements and may lead to the establishment of a Periodic System of Supramolecular Elements.

Nacnac! Who's there? A mechanistically driven approach to Suzuki–Miyaura cross‐coupling with a nacnac iron‐based catalyst enables the facile construction of C(sp³)−C(sp²) bonds with heteroaromatic boronic esters. Additional advancements allow for the construction of all carbon quaternary centers with no observable isomerization.

Abstract

Suzuki–Miyaura cross‐coupling reactions between a variety of alkyl halides and unactivated aryl boronic esters using a rationally designed iron‐based catalyst supported by β‐diketiminate ligands are described. High catalyst activity resulted in a broad substrate scope that included tertiary alkyl halides and heteroaromatic boronic esters. Mechanistic experiments revealed that the iron‐based catalyst benefited from the propensity for β‐diketiminate ligands to support low‐coordinate and highly reducing iron amide intermediates, which are very efficient for effecting the transmetalation step required for the Suzuki–Miyaura cross‐coupling reaction.

Shine on you crazy diamond ! In this Minireview a series of arene‐modifiedo ‐carboranes are described that display solid‐state emission as well as stimuli‐responsive optical properties. The unique photochemistry of these o ‐carboranes, such as aggregation‐induced emission (AIE), twist‐induced charge‐transfer (TICT) emission, and solid‐state excimer emission, is explored.

Abstract

o ‐Carborane, a cluster compound containing boron and adjacent carbon atoms, displays intriguing luminescent properties. Recently, compounds containing o ‐carborane units were found to show suppressed aggregation‐induced quenching and intense solid‐state emission; they also show potential for the development of stimuli‐responsive luminochromic materials. In this Minireview, we introduce three kinds of fundamental photochemical properties: aggregation‐induced emission, twisted intramolecular charge transfer in crystals, and environment‐sensitive excimer formation in solids. Based on these properties, several types of luminochromism, such as thermos‐, vapo‐, and mechanochromism, have been discovered. Based mainly on results from recent studies, we illustrate these mechanisms as well as unique luminescent behaviors of o ‐carborane derivatives.

A cluster with a Cu^I ₂₄ S₄₈ nanocage can be accessed in high yields using mercaptothiacalixarenes as directing ligands. The structure contains 12 Cu₂S₂ diamond core building blocks featuring exceptionally short Cu⋅⋅⋅Cu distances. Detailed NMR spectroscopic investigations revealed, for instance, that it can host small molecules like acetonitrile and methane.

Abstract

Tetramercaptotetrathiacalix[4]arene (LH₄ ) can be used as a coordination platform to bind four Cu^I ions at the thiolate and thioether S atoms. Donor ligands such as phosphanes can stabilize the resulting [LCu₄] units, which then remain monomeric ([(Ph₃PCu)₄L]). In the absence of donor ligands, they aggregate, providing a hexamer ([LCu₄]₆ ) in high yields, with a hollow‐sphere structure formed by an unprecedented Cu₂₄S₄₈ cage that is surrounded by the organic framework of the calixarene chalices. Preliminary NMR experiments with regard to the host‐guest chemistry in solution showed that the compound represents a polytopic host for acetonitrile and methane.

Recent groundbreaking studies on organoferrates have demonstrated that coordinatively unsaturated three‐coordinate σ‐alkylferrates are active catalysts in Fe‐catalyzed cross‐couplings with Grignard reagents and that pronounced solvent and counterion effects dictate metalate speciation and catalyst activity. Thanks to modern spectroscopic methods, sensitive catalyst intermediates could be analyzed.

Two from One: An operationally safe and bench‐stable crystalline diazo surrogate, difluoroacetaldehyde N‐triftosylhydrazone (DFHZ‐Tfs) was developed for in situ divergent release of two volatile diazo species, CHOCHN₂ and CF₂HCHN₂. The synthetic utility of these reagents was successfully demonstrated in the Fe‐catalyzed cyclopropanation and Doyle–Kirmse reactions. The reaction mechanism for the formation of CHOCHN₂ from CF₂HCHN₂ was elucidated by DFT calculations.

Abstract

Despite the growing importance of volatile functionalized diazoalkanes in organic synthesis, their safe generation and utilization remain a formidable challenge because of their difficult handling along with storage and security issues. In this study, we developed a bench‐stable difluoroacetaldehyde N‐triftosylhydrazone (DFHZ‐Tfs) as an operationally safe diazo surrogate that can release in situ two low‐molecular‐weight diazoalkanes, diazoacetaldehyde (CHOCHN₂) or difluorodiazoethane (CF₂HCHN₂), in a controlled fashion under specific conditions. DFHZ‐Tfs has been successfully employed in the Fe‐catalyzed cyclopropanation and Doyle–Kirmse reactions, thus highlighting the synthetic utility of DFHZ‐Tfs in the efficient construction of molecule frameworks containing CHO or CF₂H groups. Moreover, the reaction mechanism for the generation of CHOCHN₂ from CF₂HCHN₂ was elucidated by density functional theory (DFT) calculations.

Herein we report the development of a photocatalytic strategy for divergent preparation of functionalized bicyclo[1.1.1]pentylamines. This approach exploits, for the first time, the ability of nitrogen‐radicals to undergo strain‐release reaction with [1.1.1]propellane. This reactivity is facilitated by the electrophilic nature of these open‐shell intermediates and the presence of strong polar effects in the transition‐state for C–N bond formation/ring‐opening. With the aid of a simple reductive quenching photoredox cycle, we have successfully harnessed this novel radical strain‐release amination as part of a multicomponent cascade compatible with several external trapping agents. Overall, this radical strategy enables the rapid construction of novel amino‐functionalized building blocks with potential application in medicinal chemistry programs as p ‐substituted aniline bioisosteres.

Considerable efforts have been made to increase the topological complexity of mechanically interlocked molecules over the years. Three‐dimensional catenated structures composed of two or several cages are one representative example, most of them being made up of symmetric cages. However, due to the lack of an efficient yet universal synthetic strategy, interlocked structures made up of dissymmetric cages are relatively rare. Considering the space volume of the inner cavity of interlocked structure is smaller than that of its outside, we developed a novel synthetic approach with voluminous reductant NaBH(OAc) 3 that discriminates this space difference, and therefore selectively reduce the outer surface of the catenated dimer composed of two symmetric cages, thus yielding the corresponding catenane of dissymmetric‐cages. Insight into the catenation mechanism, i.e. the template effect that facilitates catenation of cages, was proved by computational and experimental techniques. We believe, our approach provides an efficient method for the synthesis of catenane of dissymmetric cages, which could potentially be utilized as synthons to engineer novel functional materials.

A general, controllable, and scalable synthesis of a family of 2D single‐layer ordered mesoporous materials (SOMMs) with completely exposed mesopores, significantly improved mass diffusion, and diverse framework composition is reported. The SOMMs are synthesized via surface‐limited cooperative assembly on water‐removable substrates of inorganic salts (e.g., NaCl), combined with vacuum filtration.

Abstract

The advantages of existing ordered mesoporous materials have not yet been fully realized, due to their limited accessibility of in‐pore surface and long mass‐diffusion length. A general, controllable, and scalable synthesis of a family of two‐dimensional (2D) single‐layer ordered mesoporous materials (SOMMs) with completely exposed mesopore channels, significantly improved mass diffusion, and diverse framework composition is reported here. The SOMMs are synthesized via a surface‐limited cooperative assembly (SLCA) on water‐removable substrates of inorganic salts (e.g., NaCl), combined with vacuum filtration. As a proof of concept, the obtained CeO₂‐based SOMMs show superior catalytic performance in CO oxidation with high conversion efficiency, ≈33 times higher than that of conventional bulk mesoporous CeO₂. This SLCA is a promising approach for developing next‐generation porous materials for various applications.

Taking shape: Cucurbit[7]uril‐threaded pseudorotaxanes containing two thiol groups at both termini polymerize by reversible disulfide bond formation into protofilament‐like linear poly‐pseudorotaxanes. These poly‐pseudorotaxanes associate laterally with each other in a self‐shape‐complementary manner to form multi‐stranded artificial microtubules.

Abstract

Hierarchical self‐assembly of building blocks over multiple length scales is ubiquitous in living organisms. Microtubules are one of the principal cellular components formed by hierarchical self‐assembly of nanometer‐sized tubulin heterodimers into protofilaments, which then associate to form micron‐length‐scale, multi‐stranded tubes. This peculiar biological process is now mimicked with a fully synthetic molecule, which forms a 1:1 host‐guest complex with cucurbit[7]uril as a globular building block, and then polymerizes into linear poly‐pseudorotaxanes that associate laterally with each other in a self‐shape‐complementary manner to form a tubular structure with a length over tens of micrometers. Molecular dynamic simulations suggest that the tubular assembly consists of eight poly‐pseudorotaxanes that wind together to form a 4.5 nm wide multi‐stranded tubule.

A diverse library of 35 N ‐benzyl aroylS ,N ‐ketene acetals with tunable color of the solid‐state emission and aggregation‐induced emission characteristics is readily synthesized by condensation of aroyl chlorides and N ‐benzyl 2‐methyl benzothiazolium salts.

Abstract

N ‐Benzyl aroyl‐S ,N ‐ketene acetals can be readily synthesized by condensation of aroyl chlorides and N ‐benzyl 2‐methyl benzothiazolium salts in good to excellent yields, yielding a library of 35 chromophores with bright solid‐state emission and aggregation‐induced emission characteristics. Varying the substituent from electron‐donating to electron‐withdrawing enables the tuning of the solid‐state emission color from deep blue to red.