P. L. Hall, J. H. Gilchrist, D. Collum
Dec 1, 1991
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Journal
Journal of the American Chemical Society
Abstract
Studies of the reactivity of lithium 2,2,6,6-tetramethylpiperidide (LiTMP) with added lithium salts are described. The E/Z selectivity of 3-pentanone enolization by LiTMP displays a marked decrease as a function of added ketone (percent conversion). The enolization also shows a notable maximum of 501 selectivity at 0.3-0.4 equiv of added LiCl and an approximate asymptotic approach to 50-6O:l selectivity when >1.0 equiv of LiBr are added. The LiTMP-LiBr complex generated from 2,2,6,6-tetramethylpiperidinium bromide affords enolates with generally high regioand stereoselectivity as shown by several representative enolizations. The selectivities appear to have exclusively kinetic origins and are suggested to stem from the intervention of LiTMP-LiX mixed aggregates characterized in the following paper.