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Synthesis of Thiazoline–Oxazoline Ligands and Their Application in Asymmetric Catalysis
Author(s) -
McKeon Seán C.,
MüllerBunz Helge,
Guiry Patrick J.
Publication year - 2011
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201101335
Subject(s) - chemistry , oxazoline , ligand (biochemistry) , enantioselective synthesis , amination , benzaldehyde , palladium , enantiomer , imine , alkylation , catalysis , combinatorial chemistry , enantiomeric excess , stereochemistry , organic chemistry , biochemistry , receptor
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.