Synthesis of chiral 1,2-diamines by asymmetric lithiation-substitution.
[reaction--see text] The imidazolidine (tetrahydroimidazole) 2, prepared in one step from N-iso-propylethylenediamine, was subjected to asymmetric lithiation and substitution using sec-butyllithium, (-)-sparteine and a range of electrophiles. Substituted imidazolidines were formed with high optical purity and could be hydrolyzed under acidic conditions to chiral, substituted ethylenediamines. Kinetic data indicate that the conformation of the carbonyl group is crucial to the extent of deprotonation, and this has implications for the lithiation of unsymmetrical carbamates and carboxylic amides.
Coldham
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I
School of Chemistry, University of Exeter, Exeter EX4 4QD, UK. i.coldham@exeter.ac.uk
Copley
R C
RC
Haxell
T F
TF
Howard
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S