Department of Organic Chemistry A. Mangini, University of Bologna, Viale Risorgimento 4, Bologna 40136, Italy.
J Org Chem. 2010 Sep 3;75(17):5927-33. doi: 10.1021/jo101261k.
Coumarins substituted by an aryl group in position 4 display restricted rotation about the Ar-C4 bond, giving rise to conformational or configurational enantiomers (atropisomers) when such a restricted motion leads to a C(1) symmetry. The dynamics of the stereomutation processes of these axial enantiomers was monitored by dynamic NMR, dynamic enantioselective HPLC, or racemization kinetics, depending on the activation energies involved. These results were further supported by DFT computations. In the two cases where the enantiomers were sufficiently long living as to be physically separated at ambient temperature, the absolute configuration was determined by means of a theoretical simulation of their electronic circular dichroism spectra (ECD).
4 位芳基取代香豆素的 Ar-C4 键旋转受到限制，当这种限制运动导致 C(1)对称性时，会产生构象或构型对映体（对映异构体）。通过动态 NMR、动态对映选择性 HPLC 或外消旋动力学监测这些轴向对映异构体的立体异构化过程的动力学，具体取决于所涉及的活化能。这些结果得到了 DFT 计算的进一步支持。在两种情况下，对映异构体的半衰期足够长，以至于可以在环境温度下物理分离，通过对它们的电子圆二色性光谱（ECD）进行理论模拟来确定其绝对构型。
