Asymmetric synthesis of 1,2-diamines by the addition of allylic zinc and magnesium reagents to N,N '-bis[(S)-1-phenylethyl)]ethanediimine

The diimine prepared by condensation of glyoxal trimer dihydrate with (S)-1 -phenylethylamine underwent double addition of allylic zinc compounds (2-bu tenyl-, 2,4-pentadienyl-, 2-methyl-2-propenylzinc bromide) in THF generally at -78 degrees C, with allylic inversion. The newly formed stereocentres a djacent to the nitrogen atoms had prevalently the R configuration. Removal of the auxiliary from the secondary 1,2-diamines with concomitant hydrogena tion of the C=C double bonds afforded the primary 1,2-diamines. The reactio n with 3-methyl-2-butenylzinc bromide gave almost exclusively the a-amino i mine from which the a-aminoaldehyde was obtained by hydrolysis. On the othe r hand, 3-methyl-2-butenylmagnesium chloride reacted at 0-20 degrees C to g ive the diamine with linear-chain substituents, owing to the reversibility of the organometallic addition.