Structure, Conformation, Stereodynamics, Dimer Formation, and Absolute Configuration of Axially Chiral Atropisomers of Hindered Biphenyl Carbinols
作者:Daniele Casarini、Lodovico Lunazzi、Michele Mancinelli、Andrea Mazzanti、Carlo Rosini
DOI:10.1021/jo701481m
日期:2007.9.1
positions were found to exist as configurationally stable atropisomers: when R = Me (7) they were separated by enantioselective HPLC and the absolute configuration assigned on the basis of the corresponding CD spectra. In solution, compounds 6 (R = H) and 7 (R = Me) were found to originate a dimer, due to H-bond interactions between two enantiomers. In the case of 7, the free energy of activation (9.5 kcal
在邻位带有单个CR 2 OH取代基的联苯衍生物的NMR光谱表明,由于绕Ar-CR 2 OH键的旋转受限制,它们以sp(更稳定)和ap(不稳定)构象异构体形式存在。当R = Et(化合物2)时,通过低温NMR光谱的线形模拟确定相应的旋转势垒(7.5kcal mol -1)。在联苯的3'位置引入前手性i- Pr基团,在2(4)位具有CMe 2 OH取代基,从而可以确定对映异构体的阻隔层(由于Ar-Ar键旋转)而对轴向不稳定手性阻转异构体(13.9 5kcal mol -1)。这些壁垒的DFT计算均与实验一致。发现在2,2'位置带有两个CR 2 OH基团的联苯以构型稳定的阻转异构体形式存在:当R = Me(7)时,它们通过对映选择性HPLC分离,并根据相应的CD光谱确定了绝对构型。在溶液中,由于两种对映异构体之间的氢键相互作用,发现化合物6(R = H)和7(R = Me)引发了二聚体。在7的情况下,活化的自由能(9