Asymmetric Transfer Hydrogenation of Aromatic Ketones Using Rhodium Complexes of Chiral N‐Heterocyclic Carbenes Derived from (S)‐Pyroglutamic Acid

Abstract

A new and flexible procedure for the preparation of chiral azolium salts derived from (S)-pyroglutamic acid has been developed. The efficiency of these ligands has been evalu-

Direct Asymmetric Hydrogenation and Dynamic Kinetic Resolution of Aryl Ketones Catalyzed by an Iridium‐NHC Exhibiting High Enantio‐ and Diastereoselectivity

“…Overall,t he herein reported catalysts not only show superior enantioselectivities when comparedt ot he only reported hydrogenation methodd eveloped by Morris and co-workers, [8] they also outperformsn early all carbene-based catalyst that rely on transfer hydrogenation. [12] Notwithstanding the results obtained with our transition-metal NHCs, preciousm etal catalysts bearing chiral phosphine ligandss till report highere nantioselectivities, [13] especially with sterically demanding substrates such as tert-alkyl ketones. [13a] To obtain mechanistic details of the hydrogenation, we performed the reaction under the optimized reaction conditions in the presence of 6bar of deuterium (Figure 2a nd Figures S1-S4 in the Supporting Information).…”

Chiral Transition‐Metal Complexes of Phenanthro‐Annulated N‐Heterocyclic Carbenes – Synthesis and Reactivity

“…Although heterogeneous catalysis is more common, homogeneous catalysts often have the advantage of milder reaction conditions and higher selectivity. [17][18][19][20] The low chiral induction is possibly because ing free carbenes 4 and 5, which were isolated without dimerization. [1][2][3][4] Particularly in the pharmaceutical chemistry, pure enantiomers are often desired.…”

“…[19,20] Another way to obtain NHC ligands that are not able to rotate about the C-N bond is to anchor the substituent to the backbone of the ligand. To avoid this problem, NHC ligands with restricted flexibility that show high enantioselectivity in various catalytic reactions have been developed by several groups.…”

Application of ferrocenylimidazolium salts as catalysts for the transfer hydrogenation of ketones

“…Transfer hydrogenation of ketones to the corresponding alcohols has become an important transformation in organometallic chemistry, especially as applied to the pharmaceutical and fine chemical industries . Much of the work conducted to date on catalytic transfer hydrogenation of ketones has utilized effective but expensive and sometimes toxic transition metals such as iridium, platinum, rhodium, gold and ruthenium . Therefore, the search for inexpensive, mild and environmentally friendly catalysts is important in order to expand the scope of available routes to achieving this important reaction.…”