Mechanistic Insight into the Anomalous<i>syn</i>-Selectivity Observed during the Addition of Allenylboronates to Aromatic Aldehydes
作者:Yusuke Sasaki、Masaya Sawamura、Hajime Ito
DOI:10.1246/cl.2011.1044
日期:2011.9.5
The reaction of enantioenriched allenylboronate 3a (98% ee) with benzaldehyde gave homopropargylic alcohol syn- and anti-4b with anomalous syn addition selectivity (anti:syn = 29:71) and high ee (98% and 97%, respectively). The stereochemical outcome in terms of the absolute configuration shows that this reaction proceeds through a cyclic transition state. Density functional theoretical (DFT) calculations were carried out to elucidate the mechanism of this anomalous syn-selectivity.
富含对映体的丙炔硼酸酯3a(99% ee)与苯甲 aldehyde 的反应生成了同丙炔醇 syn- 和 anti-4b,具有异常的 syn 加成选择性(anti:syn = 29:71)和高对映体过剩(分别为98%和97%)。从绝对构型的立体化学结果来看,该反应通过一个环状过渡态进行。进行了密度泛函理论(DFT)计算以阐明这种异常的 syn 选择性的机制。