Nature of Initial Transient Period during Enantioselective Hydrogenation on Pt and Pd

Multiphase heterogeneous catalytic enantioselective hydrogenation of acetophenone over cinchona-modified Pt/C

“…cinchonine, cinchonidine, and derivatives; Fig. 1) catalysts has been widely studied by Baiker and co-workers [1][2][3][4][5] in the case of alumina supported metals. Such catalysts were found to promote reduction and induce stereoselec-tivity in the ␣-carbonyl hydrogenation of pyruvates [6,7], ketopentolactone [8,9], other ␣-dicarbonyls [10], and, in general, on activated ketones (e.g.…”

Unexpected Inversion in Enantioselectivity in the Hydrogenation N-acetyl Dehydrophenylalanine Methyl Ester using Cinchona-Modified Pd/Al2O3 catalyst

“…Considerable effort has been focussed on the mechanism of the enantioselective hydrogenation of pyruvate esters, and three structural features of the cinchona and related modifiers that ensure they are effective in enantiodirection have been identified, namely (a) an aromatic moiety that enables adsorption on the platinum surface, (b) the absolute configuration at C(8) which controls the sense of the enantioselectivity, and (c) a basic nitrogen which is considered to interact with the substrate resulting is a 1:1 complex that is hydrogenated enantioselectively [18]. The reaction is, however, complicated by effects observed in the early part of the reaction where enantioselection increases with conversion [19][20][21][22]. However, recently, Baiker and co-workers [23][24][25] and Barto´k et al [26] have shown a further intriguing aspect of this reaction, namely that the sense of the enantioselection can be inverted for specific modifiers by changing the extent of reaction [23], the solvent [26] or the substituent at C(8) position [24,25].…”

Synthesis of Chiral Catalyst Modifiers by Hydrosilylation of Cinchonidine and Their Application in the Hydrogenation of 1‐Phenylpropane‐1,2‐dione and Ethyl Pyruvate on a Supported Pt/Al2O3 Catalyst

“…The first observed ee is slightly lower for 1 and 4a, however, this can be attributed to the well-documented initial transient behaviour of the ee at low ethyl pyruvate conversion levels. [22] All modifiers decreased the reaction rate (Table 3). The racemic reaction was up to three fold faster than the lowest modified reaction rate using 4c while being slightly slower than the reaction modified by cinchonidine.…”