Understanding 2‑(Nitromethylene)hexahydropyrimidin-5-ol\nReaction Processes and NMR Spectroscopy: A Theoretical and Experimental\nInvestigation

Ketene dithioacetals have significant applications in\nvarious fields,\nincluding natural products, pharmaceuticals, agrochemicals, and corrosion\ninhibitors. These compounds are highly valued for their reactivity\nand ability to participate in a wide range of organic syntheses. In\nthis context, the reaction between 1,3-diaminopropan-2-ol and 1,1-bismethylsulfanyl-2-nitroethylene\nhas been studied experimentally and theoretically by using density\nfunctional theory (DFT) calculations. A theoretical mechanism of formation\nof two possible products, 2-(nitromethylene)hexahydropyrimidin-5-ol\n(with a six-membered heterocycle) and (2-(nitromethylene)oxazolidin-5-yl)methanamine\n(with a five-membered heterocycle), is for the first time predicted.\nThe present DFT results indicate that both mechanisms are exothermic,\nwith energy barriers approximately 20 kcal/mol higher than those of\nthe reactants. Among the two, the formation of 2-(nitromethylene)hexahydropyrimidin-5-ol\nis energetically more favorable. This compound was synthesized and\nanalyzed by different experimental techniques (IR, nuclear magnetic\nresonance (NMR), and high-resolution mass spectrometry). The <sup>1</sup>H and <sup>13</sup>C NMR chemical shifts of 2-(nitromethylene)hexahydropyrimidin-5-ol\nwere calculated using the GIAO/B3LYP, showing good agreement with\nour experimental observations. These findings highlight an important\nmatch between experimental results and theoretical predictions, offering\ndeeper insights into ketene dithioacetal reactions. The new data and\ncontributions are expected to generate significant interest in future\napplications.