A Novel Chiral Bisphosphine-Thiourea Ligand for Asymmetric Hydrogenation of β,β-Disubstituted Nitroalkenes

Abstract

A novel chiral bisphosphine-thiourea ligand was developed and applied in the highly enantioselective hydrogenation of β,β-disubstituted nitroalkenes (up to 99% yield and 99% ee). With low catalytic loading (0.25 mol %), 98% ee and 98% conversion were obtained. The thiourea group takes on an important role in this catalytic system.

Rhodium‐Catalyzed Asymmetric Hydrogenation of Unprotected NH Imines Assisted by a Thiourea

“…Consistent with our recent report, [13] the Rh-bisphosphine complex without (thio)urea motif ( L1 ) showed very low activity and enantioselectivity (Table 1, entry 1). Urea L2 provided 22% conversion and 66% ee in sharp contrast with the thiourea L6 (Table 1, entry 2 vs. 6).…”

“…As we reported previously, [13] the catalytic system was solvent dependent and poor results were given using Ir, Pd and Ru. [14] In addition, pressures, temperatures and additives were examined to study the turnover number (TON) limit of this transformation.…”

“…[8] Most research focuses on the direct activation of neutral substrates by hydrogen bonding while recent studies take advantage of the anion binding of ion-pairing intermediates. [9] Inspired by the strategies developed in organocatalysis [10–12] and our previous research on the Rh/bisphosphine catalyzed asymmetric hydrogenation of nitroalkenes assisted by thiourea, [13] we sought to extend anion-binding catalysis to the transition metal-catalyzed asymmetric hydrogenation. We envisioned that thiourea could interact with a counterion in the catalytic pathway (Figure 2).…”

First Iridium-Catalyzed Highly Enantioselective Hydrogenation of β-Nitroacrylates

“…18 A novel bifunctional catalyst was also designed, synthesized, and applied for the rhodium-catalyzed hydrogenation. 19 β-Amino nitroalkenes were hydrogenated enantioselectively by Rh/TangPhos; 20 subsequently, an elegant iridium catalytic system was developed for this process. 21 Encouraged by these exciting results, we switched our attention to the asymmetric hydrogenation of β-nitroacrylates and envisioned that any progress in this topic will be of both fundamental and practical importance.…”

Phosphorylated (S)-tert-leucinol isophthalic diamide as a ligand for Pd-catalyzed asymmetric allylic substitution

“…For instance, thiourea P,P bi dentate ligand L A obtained via reaction of ferrocenyl aminobisphosphine with substituted phenyl isothiocyan ate shows excellent enantioselectivity in Rh catalyzed hydrogenation of nitroalkenes. 16 Amides derived from enantiomerically pure amino alcohols (these compounds are efficient organocatalysts for asymmetric reduction of ketimines with trichlorosilane and ketones with borane 17-20 ) can be regarded as suitable starting material for the introduction of the phosphorus chiral centers. Thus, phosphinite derivatives of diamides of oxalic acid with available chiral amino alcohols L B have been found to be effective in Ru catalyzed asymmetric transfer hydrogenation of aromatic ketones.…”