Elsevier

Journal of Catalysis

Volume 215, Issue 1, 1 April 2003, Pages 116-121
Journal of Catalysis

Asymmetric hydrogenation of cyclohexane-1,2-dione over cinchonidine-modified platinum

https://doi.org/10.1016/S0021-9517(02)00144-6Get rights and content

Abstract

The asymmetric hydrogenation of cyclohexane-1,2-dione over cinchonidine-modified platinum was investigated. Despite the fact that the first hydrogenation step is close to nonenantioselective, a high enantiomeric excess is obtained for the (R)-α-hydroxyketone due to kinetic resolution. In the second hydrogenation step one out of the four reactions of the network is substantially accelerated with respect to the others and with respect to the reaction in the absence of modifier, leading to an enantiomeric excess of (1R,2R)-trans-cyclohexane-1,2-diol of over 80%. Comparison with recently reported asymmetric hydrogenation of α-hydroxyethers indicates striking similarities, which hint at similar reactant–modifier interaction in both cases. The importance of cis versus trans conformation of the reactant for the reactant–modifier interaction emerges from a comparison of suggested reaction intermediates for cyclohexane-1,2-dione and butane-2,3-dione hydrogenation, respectively.

Introduction

Heterogeneous enantioselective hydrogenation using chirally modified metal catalysts is a promising route for the synthesis of optically pure compounds using a heterogeneous process. One of the most investigated catalysts for such reactions is the platinum cinchona alkaloid system [1], [2], [3], [4], [5], [6], [7], and the mechanism of enantiodifferentiation is the target of ongoing research in several laboratories. The scope of the reaction is steadily increasing, although it is still rather limited to α-keto acid derivatives and “activated” ketones.

Here we investigate the heterogeneous enantioselective hydrogenation of a cyclic vicinal diketone, cyclohexane-1,2-dione. The enantioselective hydrogenation of vicinal diketones on Pt with cinchonidine as modifier has been in the focus of several studies. Investigated diketones include butane-2,3-dione [8], hexane-3,4-dione [9], and 1-phenylpropane-1,2-dione [10]. The reduction of diketones can be a helpful tool in deducing the stereochemical requirements for fast reaction, since several reaction pathways compete, as shown in the reaction network in Fig. 1. The vicinal diketones investigated so far show considerable structural flexibility. In particular they can exist in cis and trans conformation, which makes analysis of stereochemical requirement difficult. We therefore decided to investigate cyclohexane-1,2-dione (1), which has a fixed cis conformation of the keto groups.

Several applications of the chiral hydrogenation product cyclohexane-1,2-diol (3) have been reported. (R,R)-cyclohexane-1,2-diol is used in organic synthesis as a chiral auxiliary. The conjugate addition of organocuprate reagents and Grignard reagents to α,β-unsatured esters of chiral (R,R)-cyclohexane-1,2-diol proceed with high diastereoselectivity [11], [12]. For instance, it is used as an auxiliary for the enantio- and diastereoselective synthesis of β-substituted five-, or six-membered cyclohexanecarboxylates [13]. It is further used as a photocrosslinkable chiral doping agent in liquid-crystal mixtures and in optical devices [14] and in the preparation of carbohydrate mimetics having anti-adhesive properties [15], [16].

Section snippets

Experimental

A 5 wt% Pt/Al2O3 catalyst (Engelhard 4759) was prereduced in flowing hydrogen for 90 min at 400 °C. The platinum dispersion after heat treatment was 0.27 as determined by TEM measurements. Toluene and cinchonidine were used as received (Baker, Fluka). The reactant cyclohexane-1,2-dione (1) (Avocado >98%) was distilled before use. The hydrogenation reactions were carried out in a 100-ml stainless-steel autoclave equipped with a 50-ml glass liner and PTFE cover. The reactor was magnetically

General features of the reaction

The enantioselective hydrogenation of cyclohexane-1,2-dione(1) resulted in an 81.3% enantiomeric excess (ee) in favor of (1R,2R)-trans-cyclohexane-1,2-diol ((R,R)-3) at full conversion under standard conditions. The diastereomeric excess (de) of the cis-cyclohexane-1,2-diol ((R,S)-3,(S,R)-3)) was 22.9% at complete conversion. Due to kinetic resolution the ee of the (R)-intermediate (R)-2 reached very high values, close to 100%, toward the end of the reaction. We found that the purity of the

Discussion

Rate constants for the enantioselective hydrogenation of butane-2,3-dione, based on the same reaction network as the one in Fig. 1, have previously been reported [8], which allows a comparison of the reactions of the two diones. There are similarities but also important differences. A striking similarity is the finding that for the second reaction 23 the rate constant kSR is the largest, i.e., the (S)-2→(S,R)-3 reaction is the fastest. kSR is less than four times larger than the other rate

Conclusions

The racemic and asymmetric hydrogenation of cyclohexane-1,2-dione (1) was investigated and the reaction network analyzed. In the absence of modifier the first hydrogenation step is considerably faster than the second, leading to a high intermediate concentration of the 2-hydroxycyclohexanone (2). In the presence of cinchonidine the latter is never present at high concentration due to rate acceleration of the second hydrogenation step induced by the modifier. Kinetic analysis of the reaction

Acknowledgements

Financial support by the Swiss National Science Foundation is kindly acknowledged.

References (26)

  • H.U. Blaser et al.

    Catal. Today

    (1997)
  • A. Baiker

    J. Mol. Catal. A Chem.

    (1997)
  • A. Baiker

    J. Mol. Catal. A Chem.

    (2000)
  • E. Toukoniitty et al.

    J. Catal.

    (2001)
  • M. Schürch et al.

    J. Catal.

    (1997)
  • A. Vargas et al.

    J. Catal.

    (2001)
  • T. Bürgi et al.

    J. Catal.

    (2000)
  • Y. Orito et al.

    J. Chem. Soc. Jpn.

    (1979)
  • P.B. Wells et al.

    Top. Catal.

    (1998)
  • A. Baiker et al.
  • G.J. Hutchings et al.

    Top. Catal.

    (1998)
  • M. Studer et al.

    J. Chem. Soc. Chem. Commun.

    (1998)
  • W.A.H. Vermeer et al.

    J. Chem. Soc. Chem. Commun.

    (1993)
  • Cited by (29)

    • Organogermanium compounds anchored on Pt/SiO<inf>2</inf> as chiral catalysts for the enantioselective hydrogenation of 3,4-hexanedione

      2018, Journal of Organometallic Chemistry
      Citation Excerpt :

      However, high activities and enantioselectivities only are obtained for a specific combination of active metal-chiral modifier- reagent (Pt-cinchona alkaloid-α-ketoester). Therefore, when these catalysts are employed in the reduction of diketones, the enantiomeric excess obtained is much lower than the one obtained for α-ketoesters [4-8]. Thus, the development of systems that allow the diversification of the hydrogenation reactions of prochiral compounds is a very important topic.

    • Pt-based chiral organotin modified heterogeneous catalysts for the enantioselective hydrogenation of 3,4-hexanedione

      2012, Applied Catalysis A: General
      Citation Excerpt :

      As is well known, these catalysts are particularly effective in the hydrogenation of α-ketoesters, allowing one to obtain the corresponding α-hydroxy esters with enantiomeric excesses of up to 98% [2]. To a lesser extent, these systems have been employed in the hydrogenation of α-diketones, such as 2,3-butanedione, 2,3-hexanedione, 3,4-hexanedione, 1,2-cyclohexanedione and 1-phenyl-1,2-propanodione, reaching enantiomeric excesses generally much lower than those obtained for α-ketoesters [3–7]. The hydrogenation of α-diketones presents an interesting challenge, both in terms of regio- and enantioselectivity due to the fact that these compounds have two carbonyl groups that may be hydrogenated.

    • Hydrogenation of 1-phenyl-1,2-propanedione over Pt catalysts modified by cinchona alkaloid O-ethers and the kinetic resolution of the 1-hydroxyketones generated

      2008, Journal of Catalysis
      Citation Excerpt :

      Kinetic analysis of the complex reaction systems consisting of parallel and consecutive steps is represented in the literature only by a few examples. When considering the kinetics of butane-2,3-dione [27,28] and cyclohexane-1,2-dione hydrogenation [29], at least six rate constants should be accounted for. The hydrogenation of unsymmetrical diketones, such as 1-phenyl-1,2-propanedione (PPD), is even more complex and consist of nine steps (Scheme 1).

    • Asymmetric hydrogenation of racemic 2-fluorocyclohexanone over cinchona modified Pt/Al<inf>2</inf>O<inf>3</inf> catalyst

      2006, Journal of Catalysis
      Citation Excerpt :

      However, the effect of activation by one α fluorine atom of ketones on their asymmetric hydrogenation over cinchona-modified Pt catalyst remains an open question. Based on the good enantioselectivities reported for the hydrogenation of α-keto ethers and α-hydroxy ketones bearing carbonyl groups activated by alkoxy or hydroxyl groups [20–23], we expected to find a similar effect of the α fluorine atom. Racemic 2-methoxycyclohexanone was kinetically resolved by hydrogenation over 10,11-dihydrocinchonidine-modified Pt/Al2O3; the S enantiomer reacted much faster than the R, leading to high optical purity of the hydrogenated product [20].

    • Stereoselective reduction of ketones by various vegetables

      2006, Journal of Molecular Catalysis B: Enzymatic
    View all citing articles on Scopus
    View full text