Photolytic Hydrophosphination: Insights Into Catalyzed and Uncatalyzed Processes.

In the course of studying control reactions for photocatalytic hydrophosphination, several key discoveries have been made, most notably that ambient photoexcitation cannot be ignored in future synthetic work. In this study, catalyst-free photolytic hydrophosphination is demonstrated for vinyl arenes. These reactions are less efficient than many catalyzed examples, indicating that (photo)catalysis is still highly enabling and necessary for challenging substrates. Nevertheless, these reactions appear to be closed-shell, affirming that even ambient light can impact a reaction-a potentially broad influence on even mundane reactions. Counterintuitively, polar protic solvents facilitate these reactions under thermal and photolytic conditions. An effort to extend that discovery to more classically facile substrates has revealed Click-like efficiency in polar protic (alcohol) solvents for activated alkenes, regardless of irradiation. The photochemistry and catalysis help reconcile some divergent observations in the literature. Overall, these results avail new considerations for reactions in which nucleophilic reactivity is enhanced in protic solvent, which is possible due to the absence of a discrete anion. Alcohol solvents may provide greater reactivity than aprotic polar solvents, contrary to conventional wisdom, and even ambient light may be accelerating reactions through unanticipated substrate activation.