Study of the regioselectivity and diastereoselectivity in the addition of 3-substituted-2-propenylmetal reagents to N,N′-di[1(S)-phenylethyl]ethanediimine

The additions of 3-aryl-2-propenyllithium and -zinc reagents to N,N′-di[1(S)-phenylethyl]ethanediimine in THF occurred by α and γ-addition, affording 4,5-diamino-1,7-dienes with linear and branched allylic substituents, respectively. 3-Phenoxy- and 3-alkoxy-2-propenyllithiums reacted with lack of regioselectivity, whereas the corresponding zinc reagents exclusively followed the γ-addition pathway. The (S)-configuration of the auxiliaries induced the preferential attack to the Re face of the azomethine groups. In the γ-addition route, four new stereocentres were formed and the simple (syn/anti) diastereoselectivity was dependent on the alkene geometry in the allylmetal reagents. C2-symmetric compounds with syn–syn–syn or anti–syn–anti relative stereochemistry were prevalently obtained. In contrast, when 3-ethoxy-2-propenylzinc chloride was prepared by transmetallation of the corresponding titanium reagent, a C1-symmetric compound (anti–syn–syn) was mainly formed.