Kinetic enolate formation by lithium arylamide: effects of basicity on selectivity.
Five ketones R1COCH2R2 (1a-e) were enolized in tetrahydrofuran solvent employing lithium arylamides with different electron-withdrawing and -donating substituents on the phenyl ring (4a-e). Enolate selectivity is unaffected by a moderate electron-releasing or -withdrawing group, but significantly enhanced by strong electron-withdrawing substituents to yield predominantly Z-enolate. Outstanding selectivity was achieved with lithium trichloroanilide (5) and lithium diphenylamide (6). The results are rationalized in terms of electronic effects on the tightness of the transition states.
Xie
Linfeng
L
Department of Chemistry, University of Wisconsin, Oshkosh 54901, USA. xie@uwosh.edu
Vanlandeghem
Keith
K
Isenberger
Kurt M
KM
Bernier
Carolyn
C