Preparation of Organoaluminum Reagents from Propargylic Bromides and Aluminum Activated by PbCl2 and Their Regio- and Diastereoselective Addition to Carbonyl Derivatives
作者:Li-Na Guo、Hongjun Gao、Peter Mayer、Paul Knochel
DOI:10.1002/chem.201000523
日期:2010.8.23
propargylic and allenic aluminum reagents have been easily prepared by a direct insertion of aluminum into propargylic bromides in the presence of PbCl2 (1 mol %). These organoaluminum reagents react with carbonyl compounds to afford the corresponding allenic alcohols or homopropargylic alcohols in good to excellent yields with high regio‐ and diastereoselectivity.
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。