Fillion Eric, Wilsily Ashraf, Fishlock Dan
Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.
J Org Chem. 2009 Feb 6;74(3):1259-67. doi: 10.1021/jo802311w.
Persistent intramolecular interactions between acidic C-H hydrogens and a variety of acceptors (X) (X = O, S, Br, Cl, and F) in solution were probed by (1)H NMR experiments, using 5-benzyl Meldrum's acid derivatives. To bring about formation of intramolecular C-H...X bonding, ortho-substituted benzyl Meldrum's acids were designed, for which hydrogen bonding occurred through a six-membered ring. Introduction of substituents on the aromatic moiety and in the tether allowed variation of electronic and steric factors. The superior acidity of Meldrum's acids impacted the ability of the C-H hydrogen to engage in nonclassical C-H...X bonds and drove the conformational properties of benzyl Meldrum's acid, in combination with steric factors, namely A(1,3)-allylic strain. Further understanding of intramolecular C-H...X bonds was gained by characterization of benzyl Meldrum's acids in the solid state, by X-ray analysis, and by the conformation correlated to the observations made in solution.
使用5-苄基丙二酸亚异丙酯衍生物,通过¹H NMR实验探究了溶液中酸性C-H氢与各种受体(X)(X = O、S、Br、Cl和F)之间持续的分子内相互作用。为了形成分子内C-H...X键,设计了邻位取代的苄基丙二酸亚异丙酯,其通过六元环形成氢键。在芳基部分和连接链上引入取代基,可以改变电子和空间因素。丙二酸亚异丙酯的超强酸性影响了C-H氢参与非经典C-H...X键的能力,并与空间因素(即A(1,3)-烯丙基张力)共同驱动了苄基丙二酸亚异丙酯的构象性质。通过对固态苄基丙二酸亚异丙酯进行X射线分析表征,并通过与溶液中观察结果相关的构象,进一步了解了分子内C-H...X键。