Chemoselective Synthesis of Fluorinated 1,3-Thiazines via Sonication-Assisted [3 + 3] Annulation of Thioamides and α-CF ₃ Styrene

We report a one-pot reaction of thioamides with α-trifluoromethylstyrenes to synthesize 1,3-thiazines with a fluorine atom directly incorporated into the core structure. The reaction proceeds via the SN2'/SNV pathway, preventing double defluorinative alkylation and enabling efficient cyclization under ultrasonic sonication. This method offers mild conditions, short reaction times, a broad substrate scope, high yields (up to 95%), and gram-scale applicability. DFT studies reveal kinetic control, with nitrogen attack favored over sulfur attack due to lower activation barriers.