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Asymmetric Transfer Hydrogenation of α , β ‐Unsaturated Carbonyl Compounds to Saturated Alcohols as Catalyzed by Iridium Complexes of Tricyclic Bioxazoline‐Fused Imidazole‐Derived N‐Heterocyclic Carbene Ligands
Author(s) -
Ramasamy Balasubramaniyam,
P Prakasham. A.,
Gangwar Manoj Kumar,
Ghosh Prasenjit
Publication year - 2019
Publication title -
chemistryselect
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.437
H-Index - 34
ISSN - 2365-6549
DOI - 10.1002/slct.201803293
Subject(s) - carbene , imidazole , iridium , chemistry , catalysis , medicinal chemistry , transfer hydrogenation , trifluoromethanesulfonate , ligand (biochemistry) , base (topology) , polymer chemistry , organic chemistry , ruthenium , mathematical analysis , biochemistry , receptor , mathematics
A series of chiral iridium(I) ( 1 ‐ 3 ) e complexes of bioxazoline fused imidazole derived N‐heterocyclic carbene (NHC) ligands successfully carried out asymmetric transfer hydrogenation of α , β ‐unsaturated ketones in good to excellent yields ( ca . 36‐91%) and in low enantioselectivites ( ca . 5‐31% ee ) at 1 mol % of the catalyst ( 1 ‐ 3 ) e loading in the presence of NaOH as a base in i ‐PrOH at 75° C in 3 hours of reaction time. The iridium(I) ( 1 ‐ 3 ) e complexes were synthesized directly from the bioxazoline fused imidazole derived NHC precursors namely {(3 R ,7 R )‐3,7‐di‐R‐2,3,7,8‐tetrahydrodioxazolo[3,2‐c:3′,2′‐e]imidazol‐4‐ium trifluoromethanesulfonate, R= s ‐butyl ( 1 d ), i ‐butyl ( 2 d ), i ‐propyl ( 3 d )} by the treatment with {(COD)IrCl} 2 (COD=1,5‐cyclooctadiene) in presence of t ‐BuOK as a base at room temperature. The chiral bioxazoline fused imidazole NHC ligand precursors ( 1 ‐ 3 ) d were synthesized from the commercially available optically pure amino acids by a sequence of reactions without requiring any chiral resolution.