Aminosulf(ox)ides as Ligands for Iridium(I)-Catalyzed Asymmetric Transfer Hydrogenation

Abstract

A new class of efficient catalysts was developed for the asymmetric transfer hydrogenation of unsymmetrical ketones. A series of chiral N,S-chelates (6-22) was synthesized to serve as ligands in the iridium(I)-catalyzed reduction of ketones. Both formic acid and 2-propanol proved to be suitable as hydrogen donors. Sulfoxidation of an (R)-cysteine-based aminosulfide provided a diastereomeric ligand family containing a chiral sulfur atom. The two chiral centers of these ligands showed a clear effect of chiral cooperativity. In addition, aminosulfides containing two asymmetric carbon atoms in the backbone were synthesized. Both the sulfoxide-containing beta-amino alcohols and the aminosulfides derived from 1,2-disubstituted amino alcohols gave rise to high reaction rates and moderate to excellent enantioselectivities in the reduction of various ketones. The enantioselective outcome of the reaction was favorably affected by selecting the most appropriate hydrogen donor. Enantioselectivities of up to 97% were reached in the reduction of aryl-alkyl ketones.

Iridium Diamine Catalyst for the Asymmetric Transfer Hydrogenation of Ketones

“…[7] Moreover, none of these employ simple secondary C 2 -symmetric diamines as chiral ligands. [8][9][10][11] Bearing in mind the complex developed by Ogo, Fukuzumi, and co-workers, we decided to explore the use of chiral aqua iridium complexes in ATH.…”

Enantioselective Synthesis of Alcohols and Amines by Iridium‐Catalyzed Hydrogenation, Transfer Hydrogenation, and Related Processes

“…N,S-, N,O-, P,N-, and tetradentate ligands: Van Leeuwen and co-workers have synthesized a series of N,S-chelating amino- [138,139] Variation of the substituents in 113 strongly affected the catalytic performance, and after signifi- 2 was found to give the highest enantioselectivities (up to 97 %) in 2-PrOH. When used in HCO 2 H/NEt 3 azeotrope, the opposite enantiomer was obtained (56 % ee), but only in 2 % yield.…”

A Flexible Asymmetric Synthesis of anti‐1,2‐Sulfanyl Amines

“…[6] Van Leeuwen et al, for example, synthesised two different ligands derived from cysteine and pseudo-ephedrine and used them in iridium()-catalysed asymmetric hydrogenation reactions. [7] Some diastereoselective syntheses [8] for this class of compounds have been reported, but to the best of our knowledge there is only one asymmetric synthesis. [9] One of the simplest routes is probably through treatment of thiols with aziridines in a regio-and stereoselective ringopening reaction.…”