Formation and Isomerization of 2-Azaallyllithium Reagents in Deprotonations of N-Benzyl Ketimines Containing α-Protons

Article abstract of DOI:10.1021/jo00223a024

Deprotonation of the N-benzylimine of 3-pentanone by lithium diisopropylamide (LDA) in tetrahydrofuran occurs at the benzylic position to give a 2-azaallyllithium reagent in high yield.On standing, the 2-azaallyllithium reagent isomerizes to a 1-azaallyllithium reagent.The N-benzylimine of 2-butanone can be similarly deprotonated by LDA at the benzylic position in competition with deprotonation at the α-positions to give a 2-azaallyllithium reagent in up to 22percent yield.The N-benzylimine of acetone is not appreciably deprotonated at the benzylic position by LDA.Kinetic studies of the isomerization of 2-azaallyl- to 1-azaallyllithium reagent from the 3-pentanone imine suggest that this reaction proceeds by a protonation-deprotonation sequence.