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-butenyl-, 2,4-pentadienyl-, 2-methyl-2-propenylzinc bromide) in THF generally at -78 °C, with allylic inversion. The newly formed stereocentres adjacent to the nitrogen atoms had prevalently the R configuration. Removal of the auxiliary from the secondary 1,2-diamines with concomitant hydrogenation of the C=C double bonds afforded the primary 1,2-diamines. The reaction with 3-methyl-2-butenylzinc bromide gave almost exclusively the α-amino imine from which the α-aminoaldehyde was obtained by hydrolysis. On the other hand, 3-methyl-2-butenylmagnesium chloride reacted at 0-20 °C to give the diamine with linear-chain substituents, owing to the reversibility of the organometallic addition.

allylations - amines - asymmetric synthesis - Grignard reactions - zinc