Positional Alkene Photo-Isomerization

Alkenes are ubiquitous structural features in a plenum of societally important small molecules, and abundant feedstocks that continue to shape the contours of synthetic organic chemistry. Consequently, the development of enabling methods to expedite the construction of specific stereo- and regio-isomers remains a core objective in synthetic chemistry. In contrast to the growing portfolio of de novo approaches to enable selective alkene synthesis, strategies to interconvert abundant isomers into more elusive congeners remain conspicuously underrepresented. Indeed, the development of an overarching paradigm to enable a pre-existing alkene unit to be relocated with high degrees of spatiotemporal control appears to be a moon shot. The thermochemical nuances between closely related isomeric products remain a major obstacle in realizing this objective in the ground state. Despite these palpable challenges, several examples of light-based positional isomerization reactions have emerged in recent years that enable precision relocation of alkene units to be achieved, often against a thermodynamic gradient. Although not comprehensive, it is hoped that the representative examples highlighted in this Perspective will spark interest and that the article will serve as a useful reference guide to the field. It is tempting to speculate that we are on the precipice of a watershed moment in precision positional alkene isomerization enabled by a shift to nonground-state reactivity paradigms.