Further Mechanistic Investigations into the Blue Light-Driven O-H Functionalization of Alcohols by Aryldiazoacetates

The blue light-driven O-H functionalization of alcohols by aryldiazoacetates represents a modern synthetic application of diazo photochemistry. Previous work by us and the Koenigs group demonstrated that this chemistry occurs through a free singlet carbene intermediate generated from the photolysis of the aryldiazoacetate. However, there is significant controversy in the literature concerning the exact photochemical pathway through which the photolysis of aryldiazoacetates occurs, with at least three proposed mechanisms in the literature. One group argued that photolysis requires protonation of the carbonyl to occur, another group described the C-N bond-breaking occurring on T₁ after intersystem crossing from S₁, and a third group argued that the singlet carbene is generated on S₀ after internal conversion from S₁. Additionally, no mechanistic explanation exists in the literature for the dependence of the O-H functionalized product yield on the chemical structure of the aryldiazoacetate. In this paper, we apply high-level quantum chemical methods to develop a refined picture of aryldiazoacetate photolysis and to build a mechanistic explanation for what controls the O-H functionalized product yield. Overall, our work provides new insights into an important chemical transformation initiated by the absorption of visible light.