Construction of Spiro Systems from Tetrathiafulvalene Derivatives by a Pinacol-like Rearrangement

An efficient and generalized pinacol-like rearrangement of tetrathiafulvalene (TTF) derivatives has been achieved using 2, 2, 6, 6-tetramethylpiperidine oxide (TEMPO) as a key reagent, in place of a traditional metal catalyst. Examination of numerous TTF derivatives demonstrates the reaction's exceptional tolerance to a variety of substituents, achieving an overall yield of up to 97%. The optimization of reaction conditions and evaluation of reaction applicability were achieved by varying factors such as the redox potential (E11/2) of the substrate molecule, substituent type, substituent position, number of substituents, and structural symmetry. Additionally, the reaction mechanism was explored using isotopic labeling, real-time monitoring UV-Vis absorption spectroscopy, and X-ray diffraction (XRD) analysis. Specifically, TTF is oxidized to TTF+• by p-toluenesulfonic acid (TsOH·H2O). TTF+• subsequently reacts with TEMPO and H2O to form a pinacol-like intermediate, which undergoes a rearrangement to release a 2, 2, 6, 6-tetramethylpiperidin-1-ol (TEMPOH) molecule, forming the rearranged product as a hydrogenated cation, this intermediate undergoes deprotonation, leading to the formation of the final spiro product. This investigation led to the identification of a class of reactions for the efficient conversion of TTF derivatives into their spiro products via pinacol-like rearrangement reaction.