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. Issue 1 (8th January 2019)

• Record Type: Journal Article
• Authors: Ramasamy, Balasubramaniyam; P, Prakasham. A.; Gangwar, Manoj Kumar; Ghosh, Prasenjit
• Is Part Of: ChemistrySelect. Volume 4:Issue 1(2019)
• Page Start: 357
• Page End: 365
• Publication Date: 2019-01-08
• Subjects: Iridium -- Mass spectrometry -- N-Heterocyclic carbene -- Transfer hydrogenation -- α, β-Unsaturated ketones; Chemistry -- Periodicals; 540.5
• DOI: 10.1002/slct.201803293
• Languages: English
• ISSNs: 2365-6549

Abstract

Abstract: 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. Abstract : The iridium complexes of a chiral bioxazoline fused imidazole derived N−heterocyclic carbene ligands effectively catalyzed transfer hydrogenation of α, β unsaturated ketones yielding saturated alcohols in good to excellent yields with low to moderate enantiomeric selectivity.