The Origin of Diastereofacial Control in Allylboration Reactions Using Tartrate Ester Derived Allylboronates: Attractive Interactions between the Lewis Acid Coordinated Aldehyde Carbonyl Group and an
详细信息 查看全文
- 作者：Benjamin W. Gung ; Xiaowen Xue ; and William R. Roush
- 刊名：Journal of the American Chemical Society
- 出版年：2002
- 出版时间：September 11, 2002
- 年：2002
- 卷：124
- 期：36
- 页码：10692 - 10697
- 全文大小：281K
- 年卷期：v.124,no.36(September 11, 2002)
- ISSN：1520-5126
文摘
Transition-state structures for the allylboration reaction between the tartrate ester and tartramidemodified allylboronates and acetaldehyde are located at the B3LYP/6-31G* level of theory. An attractiveinteraction between the boron-activated aldehyde and the ester or amide carbonyl oxygen lone pair isfound to play a major role in the favored transition states 11a and 13. This attractive interaction appearsto be electrostatic in origin. However, an n 
* charge-transfer type of interaction has not been ruled out.The distance (2.77 Å) between the aldehydic hydrogen and the carbonyl oxygen in transition state 13 isbeyond the sum of van der Waals radii. The formyl C-H···O bond angle (109
) in this transition structuredeviates far from linearity. Therefore, hydrogen-bonding interactions between the formyl C-H and the amidecarbonyl oxygen are considered negligible. The distance (3.81 Å) between the aldehydic oxygen and theamide carbonyl oxygen in the diastereomeric, disfavored transition state 14 is also beyond the van derWaals radii, which suggests that n/n electronic repulsion plays a lesser role in stereodifferentiation in theallylboration reaction than originally proposed.
* charge-transfer type of interaction has not been ruled out.The distance (2.77 Å) between the aldehydic hydrogen and the carbonyl oxygen in transition state 13 isbeyond the sum of van der Waals radii. The formyl C-H···O bond angle (109) in this transition structuredeviates far from linearity. Therefore, hydrogen-bonding interactions between the formyl C-H and the amidecarbonyl oxygen are considered negligible. The distance (3.81 Å) between the aldehydic oxygen and theamide carbonyl oxygen in the diastereomeric, disfavored transition state 14 is also beyond the van derWaals radii, which suggests that n/n electronic repulsion plays a lesser role in stereodifferentiation in theallylboration reaction than originally proposed.