Base-Controlled Divergent Synthesis of Fluorine-Containing Benzo[4,5]imidazo[2,1‑b][1,3]thiazines from 2‑Mercaptobenzimidazoles and β‑CF3‑1,3-Enynes

A base-controlled divergent cyclization between 2-mercaptobenzimidazoles and β-CF3-1,3-enynes providing either trifluoromethylated or fluorinated benzo­[4,5]­imidazo­[2,1-b]­[1,3]­thiazines has been developed. The β-CF3-1,3-enyne, as a three-carbon synthon, underwent a 1,8-diazabicyclo[5.4.0] undec-7-ene (DBU)-catalyzed tandem hydroamination/intramolecular hydrothiolation to give CF3-substituted 3,4-dihydro-2H-benzo­[4,5]­imidazo­[2,1-b]­[1,3]­thiazine, whereas reaction with KOH afforded fluorinated 4H-benzo­[4,5]­imidazo­[2,1-b]­[1,3]­thiazine exclusively. In addition, the synthetic utility of this methodology was showcased through a variety of downstream derivatizations.