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Paper | Special issue | Vol 101, No. 2, 2020, pp.664-678
Published online, 10th October, 2019
DOI: 10.3987/COM-19-S(F)56
Protonation-Assisted Conjugate Addition of Axially Chiral Enolates: Asymmetric Synthesis of β-Lactams with Contiguous Tetrasubstituted Stereocenters from α-Amino Acids via Memory of Chirality

Pan Yang, Tomoyuki Yoshimura, Takahiro Sasamori, Norihiro Tokitoh, Kazuhiro Morisaki, and Takeo Kawabata*

*Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto, 611-0011, Japan

Abstract

A method for asymmetric synthesis of highly strained β-lactams with contiguous two tetrasubstituted stereocenters from readily available α-amino acids has been developed via MOC strategy. In situ protonation of the labile β-lactam enolate intermediates formed through 4-exo-trig cyclization of the axially chiral enolates generated from α-amino acid derivatives seems to be the key to successfully produce highly strained β-lactams. A salient feature of this transformation is that a proton source does not quench axially chiral enolate C, but accelerate the overall reaction by protonation of the intermediary β-lactam enolate D.