Enantioselektive Protonierung von γ‐Butyrolacton‐Enolaten

Abstract

Stereoselective Protonation of Carbanions, 6 [1] . — Enantioselective Protonation of γ‐Butyrolactone Enolates * The lithium enolates 3 Li – 7 Li , produced from 3–7 by LDA or LiHMDS in THF, are protonated with eleven chiral proton sources at ‐78°C in THF which produced high enantioselectivities with 1 Li and 2 Li [5] . Although the enolates ( 3 Li , 6 Li , 7 Li ) are not deuterated quantitatively [1] , 1 H‐ and 13 C‐NMR spectra in THF at ‐78°C reveal not only quantitative deprotonation ( 3 Li , 6 Li ) but also aggregation (dimerisation) and hindered rotation of the phenyl group in 3 Li . From comparison of the enantioselectivities produced by five chiral proton sources with 1 Li – 6 Li (Tab. 4) definite structure/selectivity correlations can not be derived both for the enolates and the proton sources.