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

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.