Enantioselective, (−)-sparteine-mediated deprotonation of geranyl and neryl N,N-diisopropylcarbamate: configurational stability of the intermediate lithium compounds |
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Authors: | Wenbin Zeng Dieter Hoppe |
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Affiliation: | Organisch-Chemisches Institut der Universität, Corrensstrasse 40, D-48149 Münster, Germany |
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Abstract: | (E)/(Z)-Isomeric allylic carbamate esters were deprotonated by n-butyllithium/(−)-sparteine in toluene. Trapping experiments with chlorotrimethylsilane afforded the α-substitution products, with (R)-configuration, revealing that the pro-S proton is removed predominantly to form the corresponding (S)-lithium·(−)-sparteine derivatives; kS/kR>15:1 and >7:1, respectively. A slow (S)→(R)-epimerization occurs at −78 °C (T1/2>60 min). The allylic double bond is stable to (Z)-(E) isomerization under these conditions. |
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Keywords: | (&minus )-Sparteine Allyllithium Asymmetric deprotonation Stereoselectivity |
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