847459-34-1Relevant academic research and scientific papers
Experimental and theoretical studies of the internal stereodifferentiation occurring during the lithiation of β-stereogenic alkyl carbamates. Kinetic resolutions by (-)-sparteine-mediated deprotonation
Haller, Jan,Hense, Thomas,Hoppe, Dieter
, p. 489 - 499 (2007/10/03)
The deprotonation of β-stereogenic alkyl carbamates 8 with sec-butyllithium/TMEDA proceeds kinetically controlled with differentiation between the diastereotopic protons at the α-methylene group. The lithium intermediates 9A and 9B are trapped by electrophiles to give carboxylic acid esters 10A/ B and stannanes 11A/B, 13A/B. The diastereomeric ratio of A to B is independent of the electrophile. The highest efficiency is achieved with β-aryl-β-alkyl-substituted starting compounds 8d-f. The trends in the experimentally observed diastereoselectivities are reflected by the results of semiempirical PM3 calculations on the transition states of the deprotonation reaction. - As a result of double stereodifferentiation, application of the chiral base sec-butyllithium/(-)-sparteine gives rise to efficient kinetic resolution of racemic alkyl carbamates. VCH Verlagsgesellschaft mbH, 1996.
