Synthesis of Thiazoline–Oxazoline Ligands and Their Application in Asymmetric Catalysis

✍ Scribed by Seán C. McKeon; Helge Müller-Bunz; Patrick J. Guiry

• Publisher: John Wiley and Sons
• Year: 2011
• Tongue: English
• Weight: 455 KB
• Volume: 2011
• Category: Article
• ISSN: 1434-193X
• DOI: 10.1002/ejoc.201101335

✦ Synopsis

Abstract

A series of novel ligands incorporating oxazoline and thiazoline units were synthesized in high yield by employing a convergent route, in which the key step is a microwave‐assisted palladium‐catalyzed aryl amination. The new ligands were tested in the zinc‐catalyzed Friedel–Crafts alkylation of indole with trans‐β‐nitrostyrene, inducing enantiomeric excess values of up to 69 %. The complete series of these ligands was also applied to the chromium‐catalyzed Nozaki–Hiyama–Kishi (NHK) allylation of benzaldehyde, affording enantiomeric excess values of up to 85 %. A crystal structure of the most successful ligand in this transformation bound to iron(III) was obtained and demonstrated a tridentate binding mode of the ligand. A transition state is proposed to account for the preferential formation of the (R)‐enantiomer in the NHK reaction.