Structural Consequences of the Addition of Lithium Halides in Enolization and Aldol Reactions

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• 作者：Kenneth W. Henderson ; Andrea E. Dorigo ; Qi-Yong Liu ; Paul G. Williard ; Paul von Ragu&eacute ; Schleyer ; and Peter R. Bernstein
• 刊名：Journal of the American Chemical Society
• 出版年：1996
• 出版时间：February 14, 1996
• 年：1996
• 卷：118
• 期：6
• 页码：1339 - 1347
• 全文大小：554K
• 年卷期：v.118,no.6(February 14, 1996)
• ISSN：1520-5126

文摘

Aggregates consisting of lithium halides with either lithiumamides or lithium enolates have beencharacterized by X-ray crystallography. Two structural types,solvated heterodimers and heterotrimers, have beenfound for halide/amide combinations. Two compounds containing bothlithium halide and lithium enolate have alsobeen identified as heterodimers. Using this information, wepropose a reaction sequence for enolization and subsequentaldol addition reaction involving halide-containing aggregates. Anab initio and PM3 theoretical study of modelsystems shows that solvated heterodimers between LiBr and eitherLiNH₂ or LiOC(H)=CH₂ are favored overtherespective homodimers. Calculations reveal a stable eight-memberedring transition state for the enolization stepbetween LiCl·LiNH₂ and acetaldehyde. Twoindependent transition states, a 4,8 and a 4,4,6 ring system,werecalculated for the model reaction between the heterotrimer[(LiNH₂)₂·LiCl] and acetaldehyde.Dissociation of donorsolvent was computed to require more energy for heterodimers than forhomodimers.