The synthesis of a series of 2-thiazolines was carried out under mild conditions from the corresponding thiazolidines, by a Ru-catalyzed/TBHP oxidation reaction conditions. The reaction was chemoselective towards the amine-imine oxidation and was also regioselective, affording the unsaturation at the 2-position of the heterocycle, even with thiazolidine substrates bearing ester groups at the 4-position.