The Mechanism of Electrophilic Addition of Singlet Oxygen to Unsubstituted Pyrrole

摘要

The essential role of pyrrole in comprehending the chemistry of living organisms, coal surrogates and novel drugs is indisputable. However, literature reports a few studies on its reactivity toward prominent oxidizing agents. Herein we present a comprehensive mechanistic study of oxidation of unsubstituted pyrrole with singlet oxygen (O_2 ~1Δ_g) by deploying a quantum chemical framework leading to the production of succinimide, as the major products, through a Diels-Alder addition of O_2 ~1Δ_g to the aromatic ring. Other products, comprising maleimide, hydroperoxide, formamide or epoxide adducts, appear to form via rather minor channels. Additionally, we determined that, the primary Diels-Alder channel encompasses a barrier of 41 kJ/mol with a fitted rate constant of k(T)=1.87×10~(-13) exp(-48 000/RT) cm~3 molecule~(-1) s~(-1).