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Keywords:

  • Enantioselective synthesis;
  • Aldehydes, α-substituted α,β-unsaturated;
  • Organocatalysis;
  • Dienamine activation;
  • Secondary amine;
  • Alkylation;
  • X-Ray crystallography

Abstract

The direct and enantioselective γ-alkylation of α-substituted α,β-unsaturated aldehydes proceeding under dienamine catalysis is described. We have found that the Seebach modification of the diphenyl-prolinol silyl ether catalyst in combination with saccharin as an acidic additive promotes an SN1 alkylation pathway, while ensuring complete γ-site selectivity and a high stereocontrol. Theoretical and spectroscopic investigations have provided insights into the conformational behavior of the covalent dienamine intermediate derived from the condensation of 2-methylpent-2-enal and the chiral amine. Implications for the mechanism of stereoinduction are discussed.