Investigation of Substituent Effects on the Selectivity of 4π-Electrocyclization of 1,3-Diarylallylic Cations for the Formation of Highly Substituted Indenes
作者:Chris D. Smith、Gregory Rosocha、Leo Mui、Robert A. Batey
DOI:10.1021/jo100275q
日期:2010.7.16
meta position particularly favor cyclization. There was no obvious correlation of cyclization selectivity with calculated electron densities as has been suggested for electrophilic aromatic substitution reactions. However, the calculated selectivities determined by a gas-phase (B3LYP/6-31G* + ZPVE) comparison of the relative rates of cyclization were in remarkably good agreement with the observed selectivities
在路易斯酸存在下通过电离相应的烯丙醇而生成的差异取代的1,3-二芳基取代的烯丙基阳离子经历化学选择性和区域选择性电环化反应以生成1-芳基-1 H-茚。仅具有2-取代基且2-酯和2-烷基取代基均被耐受的烯丙基阳离子才发生电环化。通常,吸电子取代基的存在使环失活并不利于环化。相反,含有给电子取代基的体系的环化选择性取决于给电子基团的性质和位置。在间位的供电子取代基特别有利于环化。如亲电子芳族取代反应所建议的,环化选择性与计算的电子密度没有明显的相关性。然而,通过气相(B3LYP / 6-31G * + ZPVE)比较环化相对速率所确定的计算选择性与观察到的选择性非常吻合。环化计算的过渡态结构与阳离子π4一致一个conrotatory electrocyclization机制。在一些涉及更多电子缺陷系统的情况下,最初形成的1 H-茚进行后续的烯烃异构化为3 H-茚。在一个实例中,发生不寻常的二聚