Pratt Lawrence M, Newman Anthony, Cyr Jason St, Johnson Harry, Miles Benjamin, Lattier April, Austin Elizabeth, Henderson Susan, Hershey Brad, Lin Ming, Balamraju Yuvaraju, Sammonds Laurel, Cheramie Jeffery, Karnes Jonathan, Hymel Ellen, Woodford Brittini, Carter Carl
Department of Chemistry, Fisk University, Nashville, Tennessee 37208, USA.
J Org Chem. 2003 Aug 8;68(16):6387-91. doi: 10.1021/jo034541t.
The effects of lithium dialkylamide structure, mixed aggregate formation, and solvation on the stereoselectivity of ketone enolization were examined. Of the lithium dialkylamides examined, lithium tetramethylpiperidide (LiTMP) in THF resulted in the best enolization selectivity. The stereoselectivity was further improved in the presence of a LiTMP-butyllithium mixed aggregate. The use of less polar solvents reduced the enolization stereoselectivity. Ab initio calculations predict LDA and LiTMP to form mixed cyclic dimers in ethereal solvents. The calculations also predict LiTMP-alkyllithium mixed aggregates to competitively inhibit the formation of less stereoselective LiTMP-lithium enolate mixed aggregates.
研究了二烷基锂酰胺结构、混合聚集体形成以及溶剂化作用对酮烯醇化立体选择性的影响。在所研究的二烷基锂酰胺中，四甲基哌啶锂（LiTMP）在四氢呋喃（THF）中产生了最佳的烯醇化选择性。在LiTMP - 丁基锂混合聚集体存在下，立体选择性进一步提高。使用极性较小的溶剂会降低烯醇化立体选择性。从头算计算预测，在醚类溶剂中LDA和LiTMP会形成混合环状二聚体。计算还预测LiTMP - 烷基锂混合聚集体会竞争性抑制立体选择性较低的LiTMP - 锂烯醇盐混合聚集体的形成。
