Bifunctional nanocrystalline MgO for chiral epoxy ketones via claisen-schmidt condensation-asymmetric epoxidation reactions

Choudary, Boyapati M. ; Kantam, Mannepalli L. ; Ranganath, Kalluri V. S. ; Mahendar, Koosam ; Sreedhar, Bojja (2004) Bifunctional nanocrystalline MgO for chiral epoxy ketones via claisen-schmidt condensation-asymmetric epoxidation reactions Journal of the American Chemical Society, 126 (11). pp. 3396-3397. ISSN 0002-7863

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Official URL: http://pubs.acs.org/doi/abs/10.1021/ja038954n

Related URL: http://dx.doi.org/10.1021/ja038954n

Abstract

Design and development of a truly nanobifunctional heterogeneous catalyst for the Claisen-Schmidt condensation (CSC) of benzaldehydes with acetophenones to yield chalcones quantitatively followed by asymmetric epoxidation (AE) to afford chiral epoxy ketones with moderate to good yields and impressive ee's is described. The nanomagnesium oxide (aerogel prepared) NAP-MgO was found to be superior over the NA-MgO and CM-MgO in terms of activity and enantioselectivity as applicable in these reactions. An elegant strategy for heterogenization of homogeneous catalysts is presented here to evolve single-site chiral catalysts for AE by a successful transfer of molecular chemistry to surface metal-organic chemistry with the retention of activity, selectivity/enantioselectivity. Bronsted hydroxyls are established as sole contributors for the epoxidation reaction, while they add on to the CSC, which is largely driven by Lewis basic O2-sites. Strong hydrogen-bond interactions between the surface -OH on MgO and -OH groups of diethyl tartrate are found inducing enantioselectivity in the AE reaction. Thus, the nanocrystalline NAP-MgO with its defined shape, size, and accessible OH groups allows the chemisorption of TBHP, DET, and olefin on its surface to accomplish single-site chiral catalysts to provide optimum ee's in AE reactions.

Item Type:Article
Source:Copyright of this article belongs to American Chemical Society.
ID Code:6662
Deposited On:22 Oct 2010 05:26
Last Modified:28 May 2011 08:57

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