The pathways for both intermediates were explored by manual chemical intuition-guided transition state (TS) search. In addition, metadynamics (MTD) simulations of the Intermediate #1 were performed with three different collective variables. The full set of results can be found in the electronic supplementary information (ESI). Various possible chemical outcomes were identified, as shown in Figure . However, only phenyl isocyanate (PhNCO) was an exothermic reaction product with a low enough barrier of 35.9 kcal/mol separating the Intermediate #1 from the products. In the case of the alternative pathway through Intermediate #2, the rate-limiting step had a barrier of 46.4 kcal/mol. Therefore, we can ignore other found products and mechanisms as highly improbable and focus on the reaction of SO 2 -catalyzed conversion of phenylnitrile oxide into phenyl isocyanate, proceeding through the Intermediate #1.