Steric shielding of an α,β-unsaturated nitrile R
2C?=?CH–CN by
tert-alkyl β-substituents (R) prevented 1,4-additions of organolithiums and showed a remarkably solvent-dependent selectivity of
tert-butyllithium (tBuLi): 1,2-addition at CN and α-deprotonation occurred almost equally fast in THF, while CN addition was exclusive in Et
2O. The resultant
N-lithioimine was cleanly α-deprotonated (albeit with unusual slowness) in situ by an excess of tBuLi. The imine was hydrolyzed to produce an enone R
2C?=?CH–C(R')?=?O with bulky substituents R and R', which admitted CO addition but did not undergo α-deprotonation by mesityllithium,
n-butyllithium (nBuLi), and even the very strong base tBuLi. 2,4,6-Tri-
tert-butylphenyllithium (“Mes*Li”) did not add or deprotonate the enone. With
N-lithio-2,2,6,6-tetramethylpiperidine (LTMP) as the catalyst, however, Mes*Li achieved α-deprotonation simultaneously with the known Mes* radical rearrangement and a subsequent carbonyl addition. With KOH or KOtBu as a base in [D
6]DMSO (but not in DOCH
3), the enone accomplished a rapid α-H/α-D exchange reaction at rt.
相似文献