Beyond strain release: Delocalisation-enabled organic reactivity

Strain energy has long been recognised as a fundamental driving force for organic reactions. However, the release of strain alone is an insufficient predictor of reactivity, as seen in the equivalent strain energies but disparate reactivity of cyclopropane and cyclobutane. Here we show that electronic delocalisation is a key factor that operates alongside strain release to boost reactivity, significantly lowering the energy required for bond-breaking in cyclopropanes, cycloalkynes and cycloalkenes. Consideration of thermodynamic and delocalisation parameters explains the relative rates of reaction of molecules containing these functional groups, leading to a ‘hierarchy of delocalisation’ and a rule-of-thumb model that accurately predicts activation barriers. The implications of these principles are demonstrated in the context of the reactions of strained building blocks commonly encountered in total synthesis, medicinal chemistry, polymer science and bioconjugation.

Strain-Release Arylations for the Bis-Functionalization of Azetidines

The addition of nucleophilic organometallic species onto in situ generated azabicyclobutanes enables the selective formation of 3-arylated azetidine intermediates through strain-release. Single pot strategies were further developed for the N-arylation of resulting azetidines, employing either SNAr reactions or Buchwald-Hartwig couplings.

Fabrication of Inkjet-Printed Carbon Nanotube for Enhanced Mechanical and Strain-Sensing Performance

This paper presents fabrication of inkjet-printed carbon nanotube film on flexible substrate for wearable electronics applications. The density of CNT films is optimized by droplet spacing (DS) and multiple passes to provide the best strain behavior. It is found that low-density carbon nanotubes have fewer conductive pathways resulting in less change and low GF under applied strain. Conversely, high-density carbon nanotubes have more conductive paths, and they are not easily broken under strain, resulting in poor strain-sensing ability. The inkjet printing process can adjust uniformity and density of CNT film through DS and multiple passes to optimize its strain characteristics. The highest GF of 3.36 was obtained under strain ranging from 71 to 3128 με when CNT printed by DS of 23 μm and 20 passes. The relative change in resistance under various strains, ranging from 71 to 3128 με had a stable peak value for each 20 strain/release cycle which proved its repeatability and stability. Furthermore, inkjet-printed CNT sensors monitored human movement of various joints and distinguished bending angle demonstrating its potentially practical application in wearable electronics.

Vinylcyclopropane [3+2] Cycloaddition with Acetylenic Sulfones Based on Visible Light Photocatalysis

We describe the first intermolecular visible light [3+2] cycloaddition reaction being performed on a meta photocycloadduct employing acetylenic sulfones. The developed methodology exploits the advantages of combining UV and Visible light in a two-step sequence that provides a photogenerated cyclopropane which, through a strain-release process, generates a new cyclopentane ring while increasing significally the molecular complexity. This strategy could be extended to simpler vinylcyclopropanes.