ORGN 528 |
| Christopher T. Seto and Christopher M. Sprout. Department of Chemistry, Brown University, 324 Brook St. Box H, Providence, RI 02912 |
| Chiral N-acyl-ethylenediamines represent a new class of modular ligands. The N-acyl-ethylenediamine moiety serves as a metal binding site, while attached amino acids provide the source of chirality. Three sites of diversity on the ligands were optimized to enhance the enantioselectivity of the catalysts. The most effective ligand was synthesized in a single reaction step from inexpensive Boc-Val-OH and 2-morpholin-4-ylethylamine. This ligand (10 mol%) catalyzed the addition of alkylzinc reagents to aromatic aldehydes in up to 90% ee. A solid-phase synthesis of the N-acyl-ethylenediamines has been developed using an oxime resin. Oxime resin was first coupled with a Boc-protected amino acid. The addition of a commercially available N,N-dialkylethylenediamine provides the desired product free of the solid support. Any excess diamine is then scavenged using an isocyanate resin. This approach elevates the need for purification and provides the ligands in good yields. |
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Asymmetric Reactions and Syntheses
1:00 PM-5:00 PM, Wednesday, March 31, 2004 Anaheim Convention Center -- 303D, Oral
Division of Organic Chemistry |