Synthesis, Structural Elucidation, Cyclic Voltammetry, and Theoretical Modelling of 2-Ferrocenyl-4H-benzo[e][1,3]thiazines and 2-Aryl-4H-ferroceno[e][1,3]thiazines

2-Ferrocenyl-4H-benzo[e][1,3]thiazine and its 6,7-dimethoxy derivative were prepared by a Bischler-Napieralski-type annulation of the Mannich adducts of ferrocenecarboxamide, formaldehyde, and the corresponding thiophenol. A more efficient synthetic pathway, comprising a directed lithiation/iodination sequence followed by standard functional-group transformations and a final copper-catalyzed cyclization, was elaborated to convert [(dimethylamino)methyl]ferrocene into racemic mixtures of the first representatives of planar-chiral 4H-ferroceno[e][1,3]thiazines. A similar strategy with 2-iodobenzyl bromide as the precursor enabled a highly improved synthesis of 2-ferrocenyl-4H-benzo[e][1,3]thiazine. The relative tendency of the new ferrocene-based thiazines, composed of potential redox sites assembled in different molecular architectures, to behave as donors in single-electron transfer (SET) reactions was studied by cyclic voltammetry (CV) and DFT calculations. The results disclosed that 2-ferrocenyl-4H-ferroceno[e][1,3]thiazine can undergo two consecutive redox steps and is the most efficient reductant among the prepared models; it has the lowest first half-cell potential, the highest-energy highest occupied molecular orbital (HOMO) concentrated on the fused metallocene unit and the lowest first ionization energy.