Journal
THEORETICAL CHEMISTRY ACCOUNTS
Volume 138, Issue 7, Pages -Publisher
SPRINGER
DOI: 10.1007/s00214-019-2478-2
Keywords
Pyrrole; Singlet oxygen; Reaction mechanism; DFT
Categories
Funding
- National Computational Infrastructure (NCI)
- Pawsey Supercomputing Centre, Australia
- Australian Research Council (ARC)
- Murdoch University
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Pyrrolic compounds assume an important role in the chemistry of living organisms, coal surrogates and novel drugs. However, literature reports a few studies on their reactivity towards prominent oxidising agents. This contribution presents a comprehensive mechanistic study of the oxidation of unsubstituted pyrrole with singlet oxygen (O-2(g)1) by deploying a quantum chemical framework leading to the production of succinimide, as the major products, through a Diels-Alder addition of O-2(g)1 to the aromatic ring. Other products such as maleimide, hydroperoxide, formamide and epoxide adducts appear to form via insignificant channels. The primary Diels-Alder channel encompasses a barrier of 41kJ/mol with a fitted rate constant of k(T)=1.87x10(-13) exp(-48,000/RT)cm(3)mol(-1)s(-1). Furthermore, a kinetic study has been undertaken to investigate the influence of substituents on reaction rate of the Diels-Alder addition of singlet oxygen to a pyrrolic ring. The results clarify that electropositive substituents such as BeH and BH2 operate as -acceptors and thus deactivate the ring towards electrophilic attack of singlet oxygen. However, substituents comprising of strong -donors, e.g., NH2 and OH, destabilise the ring structure, increasing its oxidation reactivity.
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