Mechanistic elucidation of ketenimine–butynoate cycloaddition reaction: role of biradical intermediates in isotopomeric purity of benzyl (1,1a,6,6a-13C4)-6-methyl anthranilic ester
Thermal Diels–Alder reaction of vinyl ketenimines with 13C-labeled 2-butynoate, efficiently prepared from 13C4-acetoacetate via the enol triflate, rendered at 160 °C the corresponding methylanthranilic ester isotopomerically pure. However, when the reaction was run at 100 °C, 7% of isotope exchange between C6a and C5 was observed. This result is explained through a base-like catalyzed isomerization
乙烯酮亚胺与13 C标记的2-丁酸酯的热Diels-Alder反应,由13 C 4-乙酰乙酸经烯醇三氟甲磺酸酯有效制备,在160°C时得到相应的甲基邻氨基苯甲酸酯异位纯。但是,当反应在100°C进行时,观察到C 6a和C 5之间有7%的同位素交换。该结果通过炔烃到相应的丙二烯的碱样催化异构化来解释。结合DFT和耦合聚类计算表明了该机制建议的可行性。与以前的B3LYP结果相比,对于meta-GGA MPWB1K功能,观察到DFT与耦合簇活化和反应能之间的更好一致性。