An efficient synthetic chiral modifier for platinum

Abstract

A new chiral modifier pantoyl-naphthylethylamine (PNEA) was synthesized by reductive alkylation of 1-(1-naphthyl)ethylamine with ketopantolactone. Platinum-on-alumina modified by PNEA afforded 93% ee and 100% chemoselectivity in the hydrogenation of the activated carbonyl group of 1,1,1-trifluoro-2,4-pentanedione. Reductive heat treatment and ultrasonication of the catalyst, and the use of chlorinated solvents under mild conditions (10 bar, 10°C) enhanced the enantioselectivity. This is the first case in heterogeneous catalysis that a synthetic modifier gives more than 90% ee, better than the commonly used modifier of natural origin (cinchonidine or O-methyl-cinchonidine).

Chemo and enantioselective hydrogenation of fluorinated ketones on platinum modified with (R)-1-(1-naphthyl)ethylamine derivatives

“…In a preliminary work we have reached recently 93% ee in the hydrogenation of 2 under partly similar conditions [40]. It seems likely that in both reactions the enantioselectivities can be further improved by applying a more extended optimization strategy.…”

“…At best 92% ee was achieved in the hydrogenation of 2,2,2-trifluoroacetophenone [35] and 96% ee in the hydrogenation of ethyl-4,4,4-trifluoroacetoacetate [36] but in the hydrogenation of several other aliphatic fluorinated ketones the enantioselectivity was poor [37][38][39]. Pantoyl-naphthylethylamine (H, Scheme 1) has been found recently to be an efficient synthetic chiral modifier for Pt/Al 2 O 3 in the enantioselective hydrogenation of ketopantolactone (79% ee [18]) and a fluorinated ␤-diketone 2 (93% ee [40]). Here, we present a structure-selectivity study aimed at extending the application range of Pt modified by naphthylethylamine derivatives.…”

Enantioselective Heterogeneous Catalysis

“…Alkaloids (e.g., cinchonidine) α -hydroxy acids (e.g., (R, R)-tartaric acid) ketopantolactone [44], pyrrolidone-triones [45], α-ketoethers [46], α-diketones [47], and α,α,α-trifluoromethylketones [48]. The Ni/tartaric acid system is used for the hydrogenation of β-ketoesters and β-diketones [49,50].…”

Adsorption of 1‐(1‐Naphthyl)ethylamine from Solution onto Platinum Surfaces: Implications for the Chiral Modification of Heterogeneous Catalysts

“…[3,[6][7][8] From the fundamental point of view, much molecularlevel characterization has been carried out by using 1-(1-naphthyl)ethylamine (NEA), a simpler molecule that also contains the main functionalities believed responsible for the modifying behavior of the cinchona alkaloids, namely, an aromatic ring and an amine group near a chiral center. [9][10][11][12] Although less efficiently than cinchona alkaloids, NEA has also been shown to act as a chiral modifier for the hydrogenation of some a-ketoesters. [5,13,14] The working hypothesis that has emerged is that these chiral modifiers may weakly bind the reactant at the nitrogen atom of the amine group (and perhaps also at a second molecular location, possibly via hydrogen bonding), forming a complex that may adsorb on the surface of the metal phase of the catalysts through the aromatic ring.…”