Lithiation of Aldimines and Ketimines with LDA

The imine (0.11 mol, Exp. 7 and Note 1) dissolved in 30 ml of THF is added in one portion to a solution of 0.1 mol of LDA (Vol. 1, Chap. I) in 60 ml of THF and 66 ml of hexane (Note 2), cooled at — 55 °C. The cooling bath is removed and the temperature allowed to rise to +15°C. After an additional 10 min (aldimines) or 30 min (ketimines), the light-yellow (aldimines) to dark-yellow (ketimines) solution is used for reactions with electrophiles (Note 3). 

Especially CH3CH=N—t-Bu and C2H5CH=N—t-Bu undergo decomposition during storage, even at — 20 °C, so that redistillation before use may be necessary. 

instead of the imine CH3CH=N—f-Bu, LDA is used in excess, a corresponding amount of dialkylation product is formed in the reactions with alkyl halides the metallations of the other imines are carried out with a 5% molar excess of LDA. 

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