Imidazolium ion tethered TsDPENs as efficient ligands for Iridium catalyzed asymmetric transfer hydrogenation of α-keto phosphonates in water

Abstract

For the first time, an efficient method has been developed by the use of imidazolium ion tethered TsDPENs as efficient ligands for iridium-catalyzed asymmetric transfer hydrogenation (ATH) of α-ketophosphonates in water. The reaction provided the desired product α-hydroxyphosphonates in moderate to good yields (44-78%) and good to excellent enantioselectivities (up to >99% ee) under mild reaction conditions without adding any surfactants. The enantiomeric excess was determined by 13 P NMR by using (-)-cinchonidine as chiral solvating agent, which is a much more convenient method than chiral HPLC.

Catalytic Organic Reactions in Water toward Sustainable Society

“…Xiao and co-workers discovered that chiral iridium and rhodium species with a tosyl diphenylethylenediamine (Ts-DPEN) ligand efficiently catalyzed the asymmetric hydrogenation of ketones (Scheme 78). 264 Further water-soluble ligands for iridium(III)-catalyzed hydrogenation have been designed by Zhou and co-workers with an ammonium tag, 265 Ni and co-workers with an imidazolium tag, 266 and Friedrich and co-workers with a halfsandwich structure. 267 Dehydrogenation of alcohols has also been reported using iridium(III) catalysts.…”

“…Further water-soluble ligands for iridium­(III)-catalyzed hydrogenation have been designed by Zhou and co-workers with an ammonium tag, Ni and co-workers with an imidazolium tag, and Friedrich and co-workers with a half-sandwich structure …”

Asymmetric Transfer Hydrogenation as a Key Step in the Synthesis of the Phosphonic Acid Analogs of Aminocarboxylic Acids

“…Despite the significant general advantages of asymmetric transfer hydrogenation (ATH) [26,27] over AH and its particularly good performance in the hydrogenation of challenging substrates, [28,29] the ATH of α‐oxo‐phosphonates was never considered as a key strategy for the synthesis of α‐aminophosphonates. The ATH of α‐oxo‐phosphonates is generally underexplored with only two literature reported examples [30,31] …”

Ru(II)-Catalyzed Enantioselective Transfer Hydrogenation of α-Ketophosphonates: Straightforward Access to Valuable Chiral α-Hydroxy Phosphonates

“…In 2006, Ni and co-workers developed water-compatible imidazolium ion tethered N-p-tosyl-1,2-diphenylethylenediamine (TsDPEN) ligands for iridium-catalyzed ATH of α-ketophosphonates in water. 10 This method provided the desired products in moderate yields with enantioselectivities ranging from 69% to 99% ee depending on the substitution pattern. Obviously, there is still ample room for improvement in this process, particularly in terms of expanding the substrate scope, enhancing functional group tolerance, and improving selectivity.…”

“…Moreover, the aryl acylphosphonate substrate provided the desired product in a significantly lower enantiomeric excess of 84%, proving to be a less suitable substrate. In 2006, Ni and co-workers developed water-compatible imidazolium ion tethered N - p -tosyl-1,2-diphenylethylenediamine (TsDPEN) ligands for iridium-catalyzed ATH of α-ketophosphonates in water . This method provided the desired products in moderate yields with enantioselectivities ranging from 69% to 99% ee depending on the substitution pattern.…”