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  • Ketone enolization with lithium dialkylamides: the effects of structure, solvation, and mixed aggregates with excess butyllithium.

Ketone enolization with lithium dialkylamides: the effects of structure, solvation, and mixed aggregates with excess butyllithium.

The Journal of organic chemistry (2003-08-05)
Lawrence M Pratt, Anthony Newman, Jason St Cyr, Harry Johnson, Benjamin Miles, April Lattier, Elizabeth Austin, Susan Henderson, Brad Hershey, Ming Lin, Yuvaraju Balamraju, Laurel Sammonds, Jeffery Cheramie, Jonathan Karnes, Ellen Hymel, Brittini Woodford, Carl Carter
RESUMEN

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.

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Sigma-Aldrich
n-Butyllithium solution, 2.5 M in hexanes
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