DFT Study of the Possible Mechanisms for Synthesizing α-Cyanophosphonates from β-Nitrostyrenes

In this report, the reaction mechanism of triphenylphosphite addition to β-nitrostyrene is theoretically investigated. The M062X method, a subset of density functional theory (DFT), and the def2svp basis set are used to determine the appropriate mechanism. Three plausible mechanistic routes, labeled pathways A, B, and C, are proposed. In pathway A, triphenyl phosphite is added to the β-position of β-nitrostyrene. Pathway B involves the addition of the triphenyl phosphite molecule to the oxygen of the nitro group in β-nitrostyrene. In pathway C, triphenyl phosphite is added to the nitrogen of the β-nitrostyrene compound. Since the reaction requires the presence of two mmol of triphenyl phosphite to form the desired product, all three routes of the proposed mechanism are designed accordingly. In the gas phase, the overall energy barriers of paths A and B are 19.31 and 43.47 kcal mol⁻¹, respectively, while no reliable transition state is obtained for path C. For path A in different solvents, the overall energy barriers are 20.75, 20.76, and 20.76 kcal mol⁻¹, respectively in water, methanol, and dimethylformamide. Therefore, path A is a more favorable path, and there is not a meaningful difference between the results of the gas phase and different solvents.