cg300207d - Article pubs.acs.org/crystal Prediction of Soai...

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Prediction of Soai Reaction Enantioselectivity Induced by Crystals of N -(2-Thienylcarbonyl)glycine Damien J. Carter, , Andrew L. Rohl, * , , Alexander Shtukenberg, § Shudan Bian, § Chunhua Hu, § Lisa Baylon, § Bart Kahr, * , § Hiroko Mineki, Koichiro Abe, Tsuneomi Kawasaki, and Kenso Soai * , iVEC, 26 Dick Perry Avenue, Technology Park, Kensington, Western Australia 6151 Australia Nanochemistry Research Institute, Department of Chemistry, Curtin University, P.O. Box U1987, Perth, Western Australia 6845 Australia § Department of Chemistry, New York University, 100 Washington Square East, New York City, New York, 10003 United States Department of Applied Chemistry, Tokyo University of Science, Kagurazaka, Shinjuku-ku, Tokyo, 162-8601, Japan * S Supporting Information ABSTRACT: The enantioselectivity of the autocatalytic alkylation of 2- tert -butylpyrimidyl- 5-carbaldehyde, initiated by chiral crystals of N -(2-thienylcarbonyl)glycine, is predicted computationally. The results are in accord with the correlation of the stereochemical outcome of the reaction and the absolute structure of the crystals determined by the anomalous dispersion of X-rays and circular dichroism spectroscopy. ROLE OF CRYSTALS IN THE SOAI REACTION The so-called Soai reaction 1 5 is a startling example of asymmetric autocatalysis. In this process, 2-substituted pyrimidyl-5-carbaldehydes such as 2- tert -butylethynylpyrimi- dine-5-carbaldehyde ( 1 ) are alkylated with dialkyl zinc to give alcohols such as R / S -2- tert -butylethynyl-5-pyrimidyl alkanol ( 2 ) in large enantiomeric excess (Scheme 1). The slight stochastic deviations from ideal racemic mixtures that are generated during the early stages of the generation of chiral product are sufficient, through autocatalysis, to produce homochiral product. 6 8 The stereochemical outcome of the reaction is not deterministic until slight dissymmetric biases 9 12 are introduced either by the addition of enantiopure product or by the intercession of some other chiral influence, for instance, suspended particles ground from a single chiral crystal. The Soai reaction can be heterogeneously directed by the surfaces of chiral crystals such sodium chlorate, 13 sodium bromate, 14 quartz, 15,16 benzil, 17 hippuric acid, 18 cytosine, 19 1,1 - binaphthyl, 20 and a variety of organic co-crystals. 21 Nearly any chiral crystal will do. Dextrotatory quartz or sodium chlorate produce alcohols with the S -configuration, whereas levorotatory quartz or NaClO 3 produce alcohols with the R -configuration. Thus, the asymmetric autocatalytic Soai reaction gives abundant evidence of enantioselective adsorption of organic compounds to a variety of crystals, 22 38 but adsorbate crystal interactions have yet to be described. Here, we examine how computational crystallography can address some of these mechanisms.
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cg300207d - Article pubs.acs.org/crystal Prediction of Soai...

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