Volume 2 Issue 1, January 2023

The use of step count as a metric of synthetic efficiency carries opportunities and challenges. Here, proposals are made to standardize what constitutes a synthetic step and how steps are counted. These proposals may be beneficial in the holistic evaluation of published synthetic routes.

The Paternò–Büchi reaction is a useful approach in organic synthesis to prepare oxetanes. Understanding the mechanism of this reaction is required for the prediction and control of the diastereoselectivity of the products.

Chiral tetrahedral carbon atoms bearing functional groups amenable to functionalization offer numerous synthetic opportunities. Catalysed by copper pyridine-bis(oxazoline) complexes, the developed alkynylallylic substitution provides 3-substituted 1,4-enynes with excellent regio- and stereocontrol.

A method for the kinetic resolution of diverse planar chiral multisubstituted metallocenes through Rh-catalysed asymmetric C–H arylation of pre-functionalized metallocenes is developed. This general strategy allows for the synthesis of planar chiral 1,2- and 1,3-disubstituted metallocenes bearing a wide range of functional groups.

Isolating 2D materials from non-van der Waals (non-vdW) layered structures by mechanical cleavage is challenging owing to strong electronic coupling between adjacent layers. We show that mechanically sliding the layers weakens interlayer interactions, enabling delamination of a wide range of non-vdW layered structures to produce 2D sheets with unusual thickness-dependent physical properties.

Torus knots are assembled in a contra-helical tubular manner by coaxially nesting a small multistranded helix within a larger reverse helix. This approach enables the near-quantitative one-step syntheses of four iron(II)-templated trefoil knots. The spin-crossover properties of the iron(II) centres in the knots are tuneable by altering the intramolecular strain.

Controlling diastereodivergent light-driven processes remains synthetically challenging. Here, we disclose how the light source and steric parameters can be used to control the diastereoselectivity of [2 + 2] heterocycloaddition processes, such as in Paternò–Büchi reactions, and provide access to previously inaccessible stereochemical variants.

Stereoselective alkynylallylic substitution reactions are underexplored compared with propargylic and allylic substitutions. Now, a copper-catalysed intermolecular and decarboxylative alkynylallylic amination, alkoxylation and alkylation strategy has been developed for the synthesis of chiral 1,4-enynes. Mechanistic studies suggest that the formation of a dinuclear copper allenylidene is the rate-limiting step.

Asymmetric C–H functionalisation provides efficient synthetic routes to chiral metallocenes; however, these methods are often limited by the substitution patterns that can be accessed. Now, a Rh-catalysed enantioselective C–H arylation provides access to chiral 1,2-disubstituted and 1,3-disubstituted metallocenes via kinetic resolution of pre-functionalised metallocenes.

Mechanical cleavage of layered materials to obtain two-dimensional (2D) sheets is restricted to materials with interlayer interactions dominated by van der Waals (vdW) forces. Here, calendering is used to weaken interlayer binding in non-vdW layered structures (metals, semiconductors and superconductors) allowing mechanical exfoliation to obtain 2D sheets with thickness-dependent properties.

Reactions induced by σ-aromaticity are uncommon compared with those induced by π-aromaticity. Now, a π- and σ-aromaticity relay strategy is developed to realize the ring contraction of metallacyclobutadiene to metallacyclopropene. This reaction involves the release of π-antiaromaticity to afford a π-aromatic intermediate, followed by ring reclosure to form σ-aromatic metallacyclopropene.