Photoinduced chemical reactions provide green alternatives to traditional reaction conditions as well as open up routes towards new products that would be difficult to make otherwise. Recent work by Koenigs and coworkers demonstrated that under irradiation with blue-light, aryldiazoacetates can induce the O-H functionalization of alcohols. Using careful spectroscopic analysis, they correlated reactivity with the strength of the hydrogen-bonding between the aryldiazoacetate and the alcohol prior to light absorption. Because the aryldiazoacetates were observed to preferentially react with alcohols as opposed to alkenes, they speculated that the reaction occurs via excited state proton transfer from the alcohol to the aryldiazoacetate.<br/>Using time-dependent density function theory, we show that the electronic excitation of aryldiazoacetate is inconsistent with it behaving as a photobase. Instead, we argue that the reaction proceeds via a carbene intermediate produced through the photolysis of the aryldiazoacetate. Using density functional theory calculations performed at the ωB97M-(2)/def2-QZVPP//ωB97X-D/def2-SVPD level of theory, we demonstrate that the reaction between the singlet state of the carbene intermediate and the alcohol is thermodynamically favorable and very fast. Moreover, we provide a rationalization for the carbene intermediate’s preferential reaction with alcohols over alkenes. Overall, this work provides a refined mechanistic understanding of an interesting photochemical transformation.

Computationally probing the mechanism for the photoinduced reactions of aryldiazoacetate with alcohols: Photobasicity or carbene chemistry

ACS Spring 2022

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