Addition of Chiral Allenylzinc Reagent to Acetaldehyde: Diastereotopic Cyclic Transition States with a Tetrahedral Zinc Atom Located by ab Initio and Density Functional Theory
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- 作者：Benjamin W. Gung ; Xiaowen Xue ; Nina Knatz ; and James A. Marshall
- 刊名：Organometallics
- 出版年：2003
- 出版时间：July 21, 2003
- 年：2003
- 卷：22
- 期：15
- 页码：3158 - 3163
- 全文大小：138K
- 年卷期：v.22,no.15(July 21, 2003)
- ISSN：1520-6041
文摘
Transition-state structures for the reaction between the chiral allenylzinc reagent(M)-2 and acetaldehyde are located at the B3LYP/6-31G* and HF/6-31++G** levels oftheory. A tetrahedrally coordinated zinc atom in the transition state is found to giveenergy differences that are most consistent with the observed results. The tetrahedralzinc atom with the coordination of a solvent molecule also allows the staggering of thebonding sp2 carbons, which avoids the eclipsing of the aldehyde and the allenyl substituents.A fluoride ligand is used to mimic the methanesulfonate anion present in the reaction, anda methyl ether molecule is used to explicitly mimic the solvent molecule THF. The allenylcarbons in the transition states are slightly bent, despite the fact that both the starting allenylzinc reagent and the propargylic product are linear. The transition state forallenylzinc addition to acetaldehyde is "late" in comparison to cyclic transition states ofsimilar type.