Synthesis of Chiral C2-Symmetric 1,2-Diamines by the Addition of Organolithium Reagents to N,N′-Bis[(S)-1-phenylethyl]ethanediimine

The additions of alkyl-, phenyl- and vinyllithium reagents to N,N′-bis[(S)-1-phenylethyl]ethanediimine in THF at −78°C and in DME at −60°C gave high yields of 1,2-diamines with low stereocontrol. Care was taken to quench the reaction mixtures with de-aerated H2O to avoid formation of N-alkylidene-1-phenylethylamines which were formed through homolysis of the dilithium 1,2-diamides to give α-amido radicals which reacted with O2/H2O in the quenching step. Pentadienyl-, cinnamyl- and 1-trimethylsilylallyllithium reagents gave only the linear 1,2-diamines with high yields and moderate to good diastereoselectivities.