A novel and facile decay path of Criegee intermediates by intramolecular insertion reactions via roaming transition states

We have discovered a new and highly competitive product channel in the unimolecular decay process for small Criegee intermediates, CH₂OO and anti/syn-CH₃C(H)OO, occurring by intramolecular insertion reactions via a roaming-like transition state (TS) based on quantum-chemical calculations. Our results show that in the decomposition of CH₂OO and anti-CH₃C(H)OO, the predominant paths directly produce cis-HC(O)OH and syn-CH₃C(O)OH acids with >110 kcal/mol exothermicities via loose roaming-like insertion TSs involving the terminal O atom and the neighboring C-H bonds. For syn-CH₃C(H)OO, the major decomposition channel occurs by abstraction of a H atom from the CH₃ group by the terminal O atom producing CH₂C(H)O-OH. At 298 K, the intramolecular insertion process in CH₂OO was found to be 600 times faster than the commonly assumed ring-closing reaction.