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DOI: 10.1055/a-2467-6286
Asymmetric Addition of Organozinc Reagents to Aldehydes
Enantioselective Organozinc Addition to Aldehydes Using Planar Chiral [2.2]Paracyclophane-Imidazoline N,O-ligands.
Chem. Eur. J. 2024;
DOI: 10.1002/chem.202403345
Significance
Guiry and Kumar report an efficient seven-step synthesis of planar chiral [2.2]paracyclophane-imidazoline N,O-ligands, and describe the application of ligands A, B, and C in asymmetric organozinc additions to aldehydes. They identify ZnEt₂ and ZnEtPh as effective reagents for ethylation and phenylation, respectively. In aryl transfer reactions using in situ generated ZnEtPh, the diastereomeric ligands B and C exhibit matched/mismatched behavior.
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Comment
The authors note that in transition state TS1, shielding of the top face by the paracyclophane ring and the C-4 Ph group on the imidazoline promotes the organozinc reagent to attack the carbonyl group from the Re face, resulting in the observed (R)-enantiomer as the major product. In TS2, with diastereomeric ligand C, top-face shielding from the paracyclophane ring and the C-5 Ph group on the imidazoline favors attack from the Si face, producing the (S)-enantiomer as the predominant enantiomer.
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Publication History
Article published online:
20 December 2024
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