Asymmetric hydrogenation of isophorone in the presence of (S)-proline: Revival of a 20 years old reaction

Heterogeneous asymmetric hydrogenation over chiral molecule-modified metal particles

“…12,88 For the hydrogenation of α-ketone esters over CD-Pt catalysts, the CD molecule adsorbed onto Pt surface through the quinoline ring and formed a 1 : 1 substrate/modifier complex through H bonding. [25][26][27][89][90][91] For the asymmetric hydrogenation of CC bonds over Pd catalysts, the recent results for α,β-unsaturated acids, 51,92-96 2-pyrone, [45][46][47][48]54 and isophorone 63,[97][98][99][100][101][102] have advanced the understanding of the reaction mechanism and kinetics.…”

“…48 Asymmetric hydrogenation of isophorone over prolinemodified Pd catalysts represents another interesting system. 63,[97][98][99][100][101][102] It is generally agreed that kinetic resolution contributed to the enantiomeric excess, 63,[97][98][99]105 but whether it is a real asymmetric catalysis or a solely kinetic resolution process is still a matter of debate. It was previously proposed that condensation of isophorone with (S)-proline in a stoichiometric ratio formed an oxazolidinone-type intermediate, followed by diastereoselective hydrogenation of the CC bond; further decomposition of the adduct gave the enantiomer in excess (Fig.…”

“…101 A study on reaction kinetics revealed that appreciable enantioselectivity was readily obtained at lower isophorone conversions before hydrogen was consumed, implying the occurrence of asymmetric hydrogenation. 101 However, it was also suggested that the observed enantiomeric excess originated from an initially racemic hydrogenation of isophorone, followed by kinetic resolution. 97,98 In this case, the condensation product of isophorone and proline was just a spectator and had no contribution to the enantiomeric excess.…”

Study on the selective hydrogenation of isophorone

“…21 The chemical and diastereoselective hydrogenation of isophorone was proved to be the main source of trimethylcyclohexanone by the reaction rate, gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS) and preparation experiments. [21][22][23] It was stated that isophorone undergoes highly efficient asymmetric heterogeneous hydrogenation with a proline modied simple palladium catalyst. The powerful combination of the enhanced proline adsorption and kinetic second order resolution resulted in a rather high enantioselectivity (ee up to 99%).…”

Graphene-supported Pd nanoparticles: microwave-assisted synthesis and as microwave-active selective hydrogenation catalysts

“…In addition to nickel and nickel alloys, [1][2][3] Pd/ C is the most commonly used catalyst for this reaction. [4][5][6][7] However, it is difficult to get a good selectivity at the same time as obtaining good activity in such a system. 8 While the boiling point of DHIPO (462 K) is close to that of trans-3, 3, 5-trimethylcyclohexanol (467 K), a by-product, excellent selectivity to the designated product is particularly important to avoid the complicated and time-consuming product separation and purification processes.…”