Mechanistic Study of the Formation of a Phosphonate Ester Containing 2-Fluoroaniline: Theoretical Assignment of the Resulting Isomer

Abstract

For the first time, theoretical calculations have been employed for assignment of the most stable isomers ([(2S^*, 3S^*) or (2R^*, 3R^*)] and [(2S^*, 3R^*) or (2R^*, 3S^*)] of a phosphonate ester containing 2-fluoroaniline at HF/6-31G(d,p) and B3LYP/6-311++G(d,p) levels of theory. The results were showed that the compound with gauche arrangement and [(2S^*, 3S^*) or (2R^*, 3R^*)] configuration was more stable than the anti arrangement with [(2S^*, 3R^*) or (2R^*, 3S^*)] geometry. In addition, experimental ¹H, ¹³C and ³¹P NMR data along with X-ray crystallographic data of the compound were consistent with the results obtained from theoretical calculations. Kinetic studies were performed on the reaction between triphenyl phosphite, dialkylacetylene dicarboxylates in the presence of an NH-acid, namely as 2-fluoroaniline (as a protic/nucleophilic reagent) for the generation of the compound with a gauche arrangement and [(2S^*, 3S^*) or (2R^*, 3R^*)] configuration. Kinetic data were obtained spectrophotometrically and a temperature study yielded activation parameters. A mechanistic scheme is proposed which fits all the kinetic data.