Chiral organometallic reagents, XII. On the racemization of α‐hetero‐substituted benzyllithium compounds
- 1 February 1995
- journal article
- research article
- Published by Wiley in European Journal of Organic Chemistry
- Vol. 1995 (2) , 211-216
- https://doi.org/10.1002/jlac.199519950230
Abstract
Benzyllithium compounds carrying a benzylthio substituent (6), a benzylseleno substituent (8), and an isopropyl(methyl)amino substituent (14) have been generated. Racemization barriers have been determined in THF by monitoring the coalescence of signals of diastereotopic groups in the 1H‐NMR spectra. The barrier for 6 amounts to a ΔH≠ of 7.5 kcal mol−1 and ΔS≠ of −12 cal mol−1 K−1 corresponding to a ΔG of 9.9 kcal mol−1. The barrier for the other compounds investigated varies from 9 to 10 kcal mol−1. The rate‐determining step for the racemization is discussed to be the transformation of the contact ion pair to the solvent‐separated ion pair.Keywords
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