Theoretical study of fluorination reaction by diethylaminosulfur trifluoride (DAST)

First, the conformational analysis of DAST and a model compound, in the gas phase, were performed; the model compound was created to simplify the calculations, assuming that the behavior of the original molecule is preserved. Next, two different ways for the decomposition of the intermediate formed in the first step of the reaction were investigated: decomposition by internal nucleophilic substitution (Sni), and bimolecular nucleophilic substitution (Sn2). Finally, the inclusion of solvent effects in the mechanism was considered. The calculations show that the presence of the ethyl groups is not important to the formation of the intermediate of the reaction, but affect the decomposition of that species; furthermore, the formation of fluorinated product is favored by the Sn2 mechanism, once the fluoride ion is present.