Enols and thioenols of substituted cyanomonothiocarbonylmalonamides: structures, enolization vs. thioenolization, equilibria and conformations
作者:Ahmad Basheer、Zvi Rappoport
DOI:10.1039/b717556f
日期:——
Condensation of organic isothiocyanates with cyanoacetamides gave 24 N- and N′-substituted cyanomonothiocarbonylmalonamides in different tautomeric ratios i.e., amide–thioamides (TMA) R3NHCSCH(CN)CONR1R2 (12), thioamide–enols of amides (E) R3NHCSC(CN)C(OH)NR1R2 (11) or amide–thioenols (TE) R3NHC(SH)C(CN)CONR1R2 (13). The equilibrium constants (Kthioenol = [TE]/[TMA] and Kenol = [E]/[TMA]) in solution depend on R1, R2, R3 and the solvent. The %(E + TE) for NR1R2 increases in the order NMe2 < NHMe < NH2. The (Kthioenol + Kenol) in various solvents follows the order CCl4 > CDCl3 > C6D6 > THF-d8 > (CD3)2CO > CD3CN > DMF-d7 > DMSO-d6. The δ(OH) values are 16.46–17.43 and the δ(SH) values are 3.87–5.26 ppm in non polar solvents, e.g., CDCl3 and 6.34–6.97 ppm in THF-d8 and CD3CN. An intramolecular O–H⋯O hydrogen bond leads to the preferred Z-configuration of the enols, and an N–H⋯O bond stabilizes the thioenols’ preferred E-configuration with a non-bonded SH in solution. X-Ray crystallography revealed that systems with high %(E + TE) in solution mostly display the enols 11 in the solid state and systems with lower %(E + TE) in solution display structure 12. The differences in δ(OH), δ(NH), Kenol and crystallographic data for analogous enol and thioenol systems are compared.
将有机异硫氰酸酯与氰基乙酰胺缩合,可得到 24 种不同同分异构体比例的 N-和 N′-取代的氰单硫代羰基丙二酰胺,即酰胺-硫代酰胺(TMA)R3NHCSCH(CN)CONR1R2(12)、酰胺-硫代烯醇(E)R3NHCSC(CN)C(OH)NR1R2(11)或酰胺-硫代烯醇(TE)R3NHC(SH)C(CN)CONR1R2(13)。溶液中的平衡常数(Kthioenol = [TE]/[TMA] 和 Kenol = [E]/[TMA] )取决于 R1、R2、R3 和溶剂。NR1R2 的 %(E + TE) 按 NMe2 < NHMe < NH2 的顺序增加。各种溶剂中的(Kthioenol + Kenol)依次为 CCl4 > CDCl3 > C6D6 > THF-d8 > (CD3)2CO > CD3CN > DMF-d7 > DMSO-d6。在非极性溶剂(如 CDCl3)中,δ(OH)值为 16.46-17.43,δ(SH)值为 3.87-5.26 ppm,在 THF-d8 和 CD3CN 中为 6.34-6.97 ppm。分子内的 O-H⋯O 氢键导致了烯醇的首选 Z 构型,而 N-H⋯O 键则稳定了硫代烯醇的首选 E 构型,在溶液中形成了无键 SH。X 射线晶体学显示,溶液中含高%(E + TE)的体系在固态下大多显示烯醇 11,而溶液中含低%(E + TE)的体系则显示结构 12。比较了类似烯醇和硫代烯醇体系在 δ(OH)、δ(NH)、Kenol 和晶体学数据方面的差异。