Reversible catalysis: back and forth

Alkene metathesis and transfer hydrogenation are archetypal reversible catalytic reactions that are used throughout the chemical sciences. However, given their utility, there are surprisingly few analogous processes applicable to other functional groups. Thus, we have endeavoured to expand the repertoire of reversible catalytic reactions and explore their value as synthetic tools. This has led to the development of Pd-catalysed aryl transfer processes that enable the single bond metathesis of both C(aryl)–S and C(aryl)–P bonds. The synthetic value of these transformations was demonstrated in the depolymerisation of polyphenylene sulphide, a commercial polymer made on a kiloton scale annually, and the late-stage modification of a complex pharmaceutical. Related work led to the design of a novel HCN surrogate for the hydrocyanation of alkenes. This process is reversible and, critically, enables selective access to the less thermodynamically stable isomer, a significant challenge in reversible catalytic reactions. Finally a carbonyl chain-walking process was discovered that enables the isomerisation of ketones. This new transformation was exploited to achieve the late-stage isomerisation of naturally occurring steroids to afford novel, unnatural steroids in one simple, synthetic procedure.