Ketone enolization with lithium dialkylamides: the effects of structure, solvation, and mixed aggregates with excess butyllithium.
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.
Pratt
Lawrence M
LM
Department of Chemistry, Fisk University, Nashville, Tennessee 37208, USA. lpratt@fisk.edu
Newman
Anthony
A
Cyr
Jason St
JS
Johnson
Harry
H
Miles
Benjamin
B
Lattier
April
A
Austin
Elizabeth
E
Henderson
Susan
S
Hershey
Brad
B
Lin
Ming
M
Balamraju
Yuvaraju
Y
Sammonds
Laurel
L
Cheramie
Jeffery
J
Karnes
Jonathan
J
Hymel
Ellen
E
Woodford
Brittini
B
Carter
Carl
C
D055598:Chemical Phenomena; D002627:Chemistry, Physical; D008401:Gas Chromatography-Mass Spectrometry; D007659:Ketones / Q000737:chemistry*; D018020:Lithium Compounds / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry; D011437:Propylamines / Q000737:chemistry; D012997:Solvents; D013237:Stereoisomerism
D007659:Ketones; D018020:Lithium Compounds; D009942:Organometallic Compounds; D011437:Propylamines; D012997:Solvents; C046771:butyllithium; C007442:diisopropylamine