All-cis 1,2,3,4,5,6-hexafluorocyclohexane is a facially polarized cyclohexane

This work was generously supported by the Engineering and Physical Sciences Research Council (EPSRC) and the European Research Council (ERC).The highest-energy stereoisomer of 1,2,3,4,5,6-hexafluorocyclohexane, in which all of the fluorines are ‘up’, is prepared in a 12-step protocol. The molecule adopts a classic chair conformation with alternate C–F bonds aligned triaxially, clustering three highly electronegative fluorine atoms in close proximity. This generates a cyclohexane with a high molecular dipole (μ = 6.2 D), unusual in an otherwise aliphatic compound. X-ray analysis indicates that the intramolecular Fax···Fax distances (∼2.77 Å) are longer than the vicinal Fax···Feq­ distances (∼2.73 Å) suggesting a tension stabilizing the chair conformation. In the solid state the molecules pack in an orientation consistent with electrostatic ordering. Our synthesis of this highest-energy isomer demonstrates the properties that accompany the placement of axial fluorines on a cyclohexane and the unusual property of a facially polarized ring in organic chemistry. Derivatives have potential as new motifs for the design of functional organic molecules or for applications in supramolecular chemistry design.PostprintPeer reviewe

Photoredox catalysis with aryl sulfonium salts enables site-selective late-stage fluorination

Photoredox catalysis, especially in combination with transition metal catalysis, can produce redox states of transition metal catalysts to facilitate challenging bond formations that are not readily accessible in conventional redox catalysis. For arene functionalization, metallophotoredox catalysis has successfully made use of the same leaving groups as those valuable in conventional cross-coupling catalysis, such as bromide. Yet the redox potentials of common photoredox catalysts are not sufficient to reduce most aryl bromides, so synthetically useful aryl radicals are often not directly available. Therefore, the development of a distinct leaving group more appropriately matched in redox potential could enable new reactivity manifolds for metallophotoredox catalysis, especially if arylcopper(iii) complexes are accessible, from which the most challenging bond-forming reactions can occur. Here we show the conceptual advantages of aryl thianthrenium salts for metallophotoredox catalysis, and their utility in site-selective late-stage aromatic fluorination