Highly Stereodivergent Approach to Both Enantiomers of 4-Substituted β-Lactams via Diastereofacially Controlled Addition of Enolates oft-Butyl Acetate to a Chiral Imine
an addition reaction of esterenolates to a chiral imine with 1,3-dioxolane, derived from (S,S)-1,4-dimethoxy-2,3-butanediol as a chiral auxiliary, could be fully regulated by the appropriate selection of metal enolates used. Addition of the lithium enolates provided (4S)-β-lactams, while the corresponding (4R)-β-lactams were obtained by the condensation of titanium enolates with the chiral imine.
Highly Stereodivergent Approach to Both Enantiomers of 4-Substituted β-Lactams via Diastereofacially Controlled Addition of Enolates of<i>t</i>-Butyl Acetate to a Chiral Imine
Addition of lithium or triisopropoxytitanium enolate derived from t-butyl acetate to a chiral imine possessing dioxolane ring as a chiral auxiliary gave (3S)-β-amino ester exclusively, whereas chlorozinc enolate underwent re-facial attack to give (3R)-isomer with good selectivity. The β-amino esters thus obtained were readily converted to the corresponding (4S)- and (4R)-β-lactams respectively without loss of the stereochemical integrity at C-4 of the β-lactam rings.