Sulfur dioxide extrusion: Exploring the mechanism behind the formation of highly reactive 5-(trifluoromethyl)azafulvenium methide intermediates

Pyrolysis reactions of 2,2-dioxo-7-(trifluoromethyl)-1H,3H-pyrrolo[1,2-c]thiazoles are presented. Thermal reactions lead to the formation of noteworthy 5-membered heterocyclic products, whose yields were higher when FVPN2 was performed compared to other synthetic pyrolysis methods, such as microwave-induced pyrolysis (MWIP) or conventional heating (reflux). Trifluoromethyl-substituted pyrroles were obtained via rearrangements of trifluoromethyl-azafulvenium-methide intermediates. The experimental Arrhenius parameters of FVPN2 are presented for the very first time, and the results enable the proposal of three distinct mechanistic pathways for the SO₂ extrusion process occurring at high temperatures. Quantum chemical calculations performed at the DFT level of theory provided a rational explanation for the observed results.