Abstract
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.
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