Computationally Probing the Mechanism of the Blue-Light-DrivenO-H Functionalization of Alcohols by Aryldiazoacetates:Photobasicity or Carbene Chemistry

Photochemistry provides green alternatives to traditional reactionconditions and opens up routes toward products that are otherwise difficult to make.Recent work by Koenigs and co-workers demonstrated the blue-light-driven O-Hfunctionalization of alcohols by aryldiazoacetates. Based on spectroscopic andcomputational analyses, Koenigs and co-workers demonstrated that the alcoholsform a hydrogen-bonding complex with aryldiazoacetates prior to the lightabsorption, with the strength of hydrogen bonding correlated with the productyield. Because methyl phenyldiazoacetate (MPDA) was observed to preferentiallyreact with alcohols over cyclopropanation with styrene, the reaction was speculatedto occur via excited-state proton transfer, with MPDA acting as a photobase. In thispaper, we use time-dependent density functional theory to show that the electronicexcited state of aryldiazoacetates is inconsistent with photobasicity. Instead, we arguethat the reaction proceeds via a carbene intermediate generated through thephotolysis of the aryldiazoacetate. Using density functional theory, we demonstrate that the reaction between the singlet state of thecarbene intermediate and the alcohol is thermodynamically favorable and very fast. Moreover, we provide a rationalization for theexperimentally observed preference for O-H functionalization with alcohols over cyclopropanation with alkenes. Overall, this workprovides a refined mechanistic understanding of an interesting photochemical transformation

Automated summary

Photochemistry provides green alternatives to traditional reaction conditions and enables the synthesis of challenging products. This study investigated the blue-light-driven O-H functionalization of alcohols by aryldiazoacetates. The researchers demonstrated the formation of a hydrogen-bonding complex between the alcohols and aryldiazoacetates, and proposed a mechanism involving carbene intermediates. The findings improve our understanding of this photochemical transformation.