Effective enantiocontrol in conjugate additions of organocuprates. Highly selective 1,5-chiral induction in the conjugate additions of cuprates to α,β-unsaturated amide derivatives of 2,2-dimethyloxazolidine chiral auxiliaries

Article abstract of DOI:10.1021/jo00102a018

α,β-Unsaturated amide derivatives of 2,2-dimethyloxazolidines, developed as new chirality-controlling auxiliaries based on the restricted rotation of the amide linkage, have been applied to the enantiocontrol of conjugate additions of lithium and magnesium cuprates. High selectivities of 1,5-chiral inductions are attained, indicating their promising synthetic potential in asymmetric synthesis. The diastereofacial selectivities depend upon the efficiency of steric shielding by the 4-substituent of the chiral auxiliary, and the reaction of (S)-4-benzyl-3-[(E)-2-butenoyl]-2,2,5,5-tetramethyloxazolidine with Ph₂CuMgBrMgBrl is exclusively lk-1,5-inductive. Use of organolithium and organomagnesium show opposite low selectivities. It is concluded that the stereochemistry of cuprate conjugate addition is determined at the step of formation of the d,π* type charge transfer complexes.