Asymmetric α-arylation of amino acid derivatives by Clayden rearrangement of ester enolates via memory of chirality.

A method for asymmetric α-arylation of amino acid derivatives has been developed. The arylation was performed by Clayden rearrangement of ester enolates via memory of chirality to give hydantoins with an aryl-substituted tetrasubstituted carbon with up to 99% ee.

Protonation-assisted conjugate addition of axially chiral enolates: asymmetric synthesis of multisubstituted ß-lactams from α-amino acids.

ß-Lactams with contiguous tetra- and trisubstituted carbon centers were prepared in a highly enantioselective manner through 4-exo-trig cyclization of axially chiral enolates generated from readily available α-amino acids. Use of a weak base (metal carbonate) in a protic solvent (EtOH) is the key to the smooth production of ß-lactams. Use of the weak base is expected to generate the axially chiral enolates in a very low concentration, which undergo intramolecular conjugate addition without suffering intermolecular side reactions. Highly strained ß-lactam enolates thus formed through reversible intramolecular conjugate addition (4-exo-trig cyclization) of axially chiral enolates undergo prompt protonation by EtOH in the reaction media (not during the work-up procedure) to give ß-lactams in up to 97% ee.