Hydroselenation of Simple Olefins: Elucidating the β-Selenium Radical Effect

We report a light-promoted hydroselenation of alkenes with high anti-Markovnikov selectivity. Spectroscopic, kinetic, and computational mechanistic studies indicate that blue light activates an aryl diselenide to generate a seleno radical; this radical adds into an alkene to form a β-seleno carbon radical. Subsequent hydrogen atom transfer (HAT) generates the linear selenide with high selectivity in preference to the branched isomer. These studies reveal a unique β-selenium effect, where a selenide β to a carbon radical imparts high anti-selectivity for radical addition through delocalization of the HAT transition state.