Carreño M Carmen, Enríquez Alvaro, García-Cerrada Susana, Sanz-Cuesta M Jesús, Urbano Antonio, Maseras Feliu, Nonell-Canals Alfons
Departamento de Química Orgánica C-I, Universidad Autónoma Madrid, Cantoblanco, 28049 Madrid, Spain.
Chemistry. 2008;14(2):603-20. doi: 10.1002/chem.200700762.
The synthesis of enantiopure C-12 methoxy- or alkyl-substituted 5,7,8,12b-tetrahydro[4]helicene quinones 16 and 17 and the 7,8-dihydroaromatic analogues 4 and 5 has been achieved from (SS)-2-(p-tolylsulfinyl)-1,4-benzoquinone. In the first series, with a structure containing both central and helical chiralities, the R absolute configuration of the stereogenic carbon atom was defined after the asymmetric cycloaddition step, whereas the P or M helicity was shown to be dependent on the nature of the C-12 substituent. The size of this group was also defining the configurational stability of the final (P)-7,8-dihydro[4]helicene quinones 4 and 5. The interconversion barriers between the P and M helimers in the latter, computed with a DFT B3LYP method, matched well with the experimentally observed stability. Our study provided evidence that, in addition to steric effects, a small but significant role of electronic effects is governing the configurational stability of such helical quinones.
已从(SS)-2-(对甲苯亚磺酰基)-1,4-苯醌实现了对映体纯的C-12甲氧基或烷基取代的5,7,8,12b-四氢[4]螺旋烯醌16和17以及7,8-二氢芳族类似物4和5的合成。在第一个系列中，其结构同时包含中心手性和螺旋手性，在不对称环加成步骤之后确定了立体中心碳原子的R绝对构型，而P或M螺旋性显示取决于C-12取代基的性质。该基团的大小还决定了最终的(P)-7,8-二氢[4]螺旋烯醌4和5的构型稳定性。使用DFT B3LYP方法计算的后者中P和M螺旋异构体之间的互变势垒与实验观察到的稳定性很好地匹配。我们的研究提供了证据，表明除了空间效应外，电子效应也起着小但重要的作用，决定着此类螺旋醌的构型稳定性。
