ISSN:
0009-2940
Keywords:
Enantiomerization
;
Organolithium compounds
;
Dynamic NMR spectroscopy
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The rate of enantiomerization of the racemic α-phenylselenoalkyllithium compound 6 has been determined by dynamic NMR spectroscopy in [D8]THF. The enantiomerization rate was found to be first order with respect to monomeric 6 and to show no conspicuous solvent dependence (diethyl ether; toluene + 1 eq. of THF) or change upon addition of LiClO4. The marked steric effects on the enantiomerization rate found with the α-duryl- and α-mesityl-selenoalkyllithium compounds 7c and 7d suggest that rotation about the carbanion-selenium bond may be the rate-determining step in those sterically hindered systems. Similar steric effects were detected for the enantiomerization of the corresponding α-arylthio- and α-aryltelluroalkyllithium compounds 7j and 7f, but are absent with the α-arylsilyl-substituted alkyllithium compound 7o. This finding, along with the fact that the phenyltelluro- (7e), phenylseleno- (6), and phenylthio-alkyllithium compounds (7g) have essentially the same enantiomerization barrier, lead us to propose that in these cases a reorganization within the contact ion pair is the rate limiting step for the enantiomerization.
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/cber.19951280903
