Conformational Studies by Dynamic Nuclear Magnetic Resonance. 59.<sup>1</sup> Stereodynamics of Conformational Enantiomers in the Atropisomers of Hindered Naphthylcarbinols
作者:Daniele Casarini、Lodovico Lunazzi、Andrea Mazzanti
DOI:10.1021/jo970113+
日期:1997.5.1
Naphthyldialkylmethanols ArRR'COH (Ar = 1-naphthyl or 1-naphthyl-2-methyl) exist as a pair of atropisomers created by the restricted rotation about the Ar-COH bond. They can be detected by low-temperature NMR spectroscopy but can also be separated as stable compounds at room temperature if both the alkyl substituents are bulky tert-butyl groups (one such example is provided by compound 1, R = R' = Bu(t) with Ar = 1-naphthyl)
萘二烷基甲醇ArRR'COH(Ar = 1-萘基或1-萘基-2-甲基)以一对阻转异构体的形式存在,这些阻转异构体是由围绕Ar-COH键的受限旋转产生的。它们可以通过低温NMR光谱进行检测,但是如果两个烷基取代基均为大的叔丁基,则它们也可以在室温下作为稳定的化合物分离(一个这样的例子由化合物1提供,R = R'= Bu(t ),其中Ar = 1-萘基)。发现这些阻转异构体相互转化的活化自由能(DeltaG())在7.6 kcal mol(-)(1)之间变化(如7中,R = R'= Me,Ar = 1-萘基-2-甲基)和32.9 kcal mol(-)(1)(与1相同)。通过差值NOE实验或利用在两种阻转异构体中相差很大的H-8化学位移来分配正周平面(sp)或反周平面(ap)结构。取决于取代基,在平衡处更稳定的物质可以是sp或ap阻转异构体。当R = R'= Pr(i)且R = R'= Et(如果Ar