Mechanistic insights into the autocatalyzed rearrangement of 2-bromooxazolines to 2-bromoisocyanates by means of high-level quantum chemical methods

A mechanism for the thermal instability and selective rearrangement of 2-bromooxazolines is proposed and examined using the highly accurate G4(MP2) thermochemical protocol. We propose this rearrangement to be autocatalyzed by bromide ions that are initially formed via a bimolecular reaction between two 2-bromooxazoline molecules. We find this step to be rate determining, and it results in a consequent and more favorable propagative reaction of bromide ions with the starting material (2-bromooxazoline). The proposed mechanism sheds light on experimental observations and provides a coherent explanation for 2-bromooxazolines thermal instability. We proceed to rationalize the high barrier of the rate-determining step via comparison with experimentally known pathways.