Asymmetric synthesis of β-lactams and pseudopeptides via stereoselective conjugate additions of lithium (a-methylbenzyl)allylamide to ct,β-unsaturated iron acyl complexes
Davies SG., Garrido NM., McGee PA., Shilvock JP.
Lithium (a-methylbenzyl)allylamide 2 undergoes stereoselective conjugate additions to u,β-unsaturated iron acyl complexes 3a-c to afford β-amino iron acyl adducts 5a-c and 6a-c. These adducts may be deallylated smoothly using palladium(O) catalysis providing the corresponding homochira! secondary amines 7a-c which, upon oxidative decomplexation with bromine or //-bromosuccinimide, undergo direct β-lactam ring formation. The diastereoselectivity for the conjugate addition to 3a may be further improved by the use of magnesium amide 10. Oxidative decomplexation of one of the β-amino iron acyl adducts 5b in the presence of u-amino esters provides pseudopeptide fragments comprising an a-amino acid coupled to a β-amino acid. © The Royal Society of Chemistry 1999.