Addition of Grignard reagents to chiral 1,2-bisimines: A diasteroselectivepreparation of unsymmetrical 1,2-diamines

A diastereoselective synthesis of tert-butyl-1,2-diamines has been develope d from the addition of tert-butylmagnesium chloride to the 1,2-bisimines de rived from glyoxal and chiral amines such as 1-(S)-ethylphenylamine, 1-(S)- phenylpropylamine or 1-(S)-(p-chlorophenyl) ethylamine. The influence of so lvent, temperature and chiral auxiliaries on the chemical reactivity and st ereoselectivity has been fully studied. Evidence of a dynamic kinetic resol ution during the bis-addition process of the organometallic, leading to the 1,2-di-tert-butylethanediamine,([1]) as a single diastereomer, has been de monstrated. This resolution has been applied with high diaster eoselectivit ies to the synthesis of unsymmetrical disubstituted 1,2-diamines, by additi on of one equivalent of tert-butylmagnesium chloride, followed by one equiv alent of a second Grignard reagent. Several chiral 1-tert-butyl-1,2-diamine s have also been synthesized by monoaddition of tert-butylmagnesium chlorid e to the bisimines, followed by hydride reduction of the chiral intermediat e imines.