Influence of the Acetylenic Substituent on the Intramolecular Carbolithiation of Alkynes: A DFT Theoretical Study

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• 作者：Catherine Fressign茅 ; Rudy Lhermet ; Anne-Lise Girard ; Muriel Durandetti ; Jacques Maddaluno
• 刊名：Journal of Organic Chemistry
• 出版年：2013
• 出版时间：October 4, 2013
• 年：2013
• 卷：78
• 期：19
• 页码：9659-9669
• 全文大小：641K
• 年卷期：v.78,no.19(October 4, 2013)
• ISSN：1520-6904

文摘

A theoretical study of the intramolecular 5-exo-dig carbolithiation of substituted propargyl o-lithioaryl ethers, leading to dihydrobenzofurans, has been performed. The results show that a DFT description of the reaction (B3P86, 6-31G**) matches the experimental data provided that an explicit solvation by two molecules of THF is considered. To take place, the cyclization also implies that the acetylenic chain adopts a conformation in which a significant interaction arises between the lithium and the C鈮 triple bond. Reaching the cyclization TS requires the passage of an activation barrier that should not be higher than 12鈥?3 kcal mol^鈥?. From a thermodynamic point of view, the reaction is exothermic whatever the substituent R (from approximately 鈭?0 to 鈭?2 kcal mol^鈥?). In the starting substrate, a supplementary interaction between the Li and a substituent at the propargylic position can develop, influencing the future double-bond configuration. Thus, derivatives exhibiting an R鈥揕i interaction tend to provide E olefins. In contrast, when no coordination between the lithium cation and the terminal R occurs, syn carbolithiation takes place, and the configuration of the exocyclic olefin is likely to be Z. This hypothesis accounts for most of the experimental results published before.