Download PDF
Synfacts 2010(9): 1029-1029  
DOI: 10.1055/s-0030-1257998
Metal-Catalyzed Asymmetric Synthesis and Stereoselective Reactions
© Georg Thieme Verlag Stuttgart ˙ New York

Catalytic Asymmetric Protonation of Chiral Calcium Enolates

Contributor(s): Hisashi Yamamoto, Dmitry L. Usanov
T. Poisson, Y. Yamashita, S. Kobayashi*
The University of Tokyo, Japan
Further Information

Publication History

Publication Date:
23 August 2010 (online)

    Permissions and Reprints

Significance

Asymmetric protonation represents a powerful methodology for constructing tertiary chiral carbon centers, with catalytic versions being of particular importance. However, excellent chiral environments should be designed for these transformations due to the steric nature of the hydrogen atom. In this paper the authors developed a highly enantioselective protocol for the catalytic asymmetric protonation of chiral calcium enolates, which were prepared in situ from amides 1 and dibenzyl malonate via 1,4-addition. 10 mol% of Ca(OEt)2, 10 mol% of phenol 2, and 11 mol% of Ph-PyBox 3 constituted the optimum system. ­Excellent yields (72-96%) and enantioselectivities (93-96% ee) were obtained for a range of substrates.