C-N軸性不斉エノラートの分子内共役付加を利用する多置換 β-ラクタムの不斉合成

抄録

  The synthesis of β-lactams with contiguous tetra- and trisubstituted carbon centers has been accomplished via the 4-exo-trig intramolecular conjugate addition of C-N axially chiral enolates generated from α-amino acid derivatives. Use of a metal carbonate in a protic solvent (i.e., Cs₂CO₃ in EtOH) was found to be critical for the success of the reaction. Under optimized reaction conditions, axially chiral enolates were generated in very low concentration, thereby favoring intramolecular conjugate addition while minimizing intermolecular side reactions. The highly strained β-lactam enolates formed through this reversible intramolecular conjugate addition were rapidly protonated by EtOH in the reaction media to afford β-lactams in up to 97% ee.