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

A base-controlled divergent cyclization between 2-mercaptobenzimidazoles and β-CF 3 -1,3-enynes providing either trifluoromethylated or fluorinated benzo[4,5]imidazo[2,1- b ][1,3]thiazines has been developed. The β-CF 3 -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 CF 3 -substituted 3,4-dihydro-2 H -benzo[4,5]imidazo[2,1- b ][1,3]thiazine, whereas reaction with KOH afforded fluorinated 4 H -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.