The synthesis of pyridothiazines was achieved using pyridinium 1,4-zwitterionic thiolates and α-functionalized bromoalkanes via a formal [5+1] pathway. Further studies demonstrated that the synthesis of indolizines could be accomplished via a stepwise [(5+1)−1] pathway with unstable pyridothiazines as the transient intermediates from the same starting materials. The net transformation involves a sequence of annulation, oxidation and ring-contraction/desulfuration.