Flexibility vs Rigidity of Singly and Doubly Tethered Biphenyls: Structure, Dynamic Stereochemistry, and Resolution of Tribenzo[<i>a</i>,<i>c</i>,<i>f</i>]cyclooctane, Tetrabenzo[<i>a</i>,<i>de</i>,<i>h</i>,<i>kl</i>]bicyclo[6.6.0]tetradecane, and Their Alkyl Derivatives
作者:Lior Eshdat、Elad Shabtai、Sadiq A. Saleh、Tamar Sternfeld、Mayuko Saito、Yoshio Okamoto、Mordecai Rabinovitz
DOI:10.1021/jo990090u
日期:1999.5.1
dihedral angles of 57.8 degrees, 56.1 degrees /58.2 degrees (two conformations), and 57.7 degrees, respectively. Semiempirical calculations (AM1) reveal higher relative strain energies and smaller biphenyl dihedral angles for the bulky alkyl substituents, which correspond to their lower DeltaG() values.
从动态(1)H NMR实验获得的三苯并[a,c,f]环辛烷(1a)对映异构体的势垒为DeltaG()= 19.5-20.1 kcal mol(-)(1)和DeltaG( )=在聚结温度下其烷基化衍生物(1b-e)的17.2-17.6 kcal mol(-)(1)。通过手性HPLC将四苯并[a,de,h,kl]双环[6.6.0]十四烷(2a)及其四乙基衍生物(2b)分离为它们的对映异构体。通过遵循纯对映体的外消旋速率获得对映体的动力学值。对于2a和2b,分别获得了DeltaG()(596)= 49.6 kcal mol(-)(1)和DeltaG()(561)= 46.3 kcal mol(-)(1)的势垒。观察到强溶剂和温度对(1)H NMR化学位移的影响。X射线晶体学显示1a,1b和2a的扭转构型,二面角为57。8度,56.1度/58.2度(两个构图)和57.7度。半经验计算(AM1)显示