Photoisomerization of Borylated Alkenes and Dienes

Abstract Photochemical isomerization is an expansive strategy to regulate the position and geometry of a preexisting alkene. Despite the operational simplicity this method confers, application in synthetic chemistry has until recently remained limited by the reliance on styrenyl-based chromophores. The emergence of borylated alkenes has enabled this limitation to be circumnavigated and provides a traceless handle for further (stereospecific) manipulations. Incorporation of a boron substituent modulates alkene photochemistry, enabling conjugation, excited-state energetics, and relaxation pathways to be understood at the level of well-defined boron-centered orbital interactions. This review discusses how the inclusion of a boron substituent can be leveraged as an active control element rather than a passive functional handle. These developments include selective manipulation of alkene geometry and position through subtle alterations to conjugation across a range of molecular contexts. Both energy transfer catalysis and direct substrate excitation can be applied to access isomers that are difficult to obtain selectively by conventional ground-state methods. By elevating boron to an active stereoelectronic design element that orchestrates excited-state reactivity, the photochemical isomerization of short borylated π-systems has emerged as an expansive strategy for structural modulation.