The reaction of the lithium derivative of (+)-(S)-p-tolyl p-tolylthiomethyl sulphoxide [(+)-(S)-(1)] with benzaldehyde and phenylacetaldehyde in tetrahydrofuran at -78 °C gives, after methylation of the hydroxy-group, reduction of the sulphoxide, and hydrolysis of the resulting dithioacetal, the corresponding α-methoxy-aldehydes, (-)-(R)-2-methoxy-2-phenylacetaldehyde and (+)-(R)-2-methoxy-3-phenylpropionaldehyde, enantiomeric excess 70 and 46%, respectively. The reaction of (+)-(S)-(1) with benzaldehyde in tetrahydrofuran at room temperature in the presence of Triton B gives the new optically pure reagent (E)-(+)-(S)-1-p-tolysulphinyl-1-p-tolylthio-2-phenylethylene [(+)-(S)-(2)], which is a chiral enolonium equivalent. The addition of sodium methoxide to (+)-(S)-(2) in methanol gives, after reduction of the sulphoxide and hydrolysis of the resulting dithioacetal, (+)-(S)-2-methoxy-2- phenylacetaldehyde, enantiomeric excess 60%. The unfavourable equilibrium in addition of methoxide to (+)-(S)-(2) means that the latter is not very useful as a chiral enolonium equilvalent in reactions of this type.
Chiral acyl anion and enolonium ion equivalents. Asymmetric synthesis of α-methoxy-aldehydes / L. Colombo, C.M.A. Gennari, C. Scolastico, G. Guanti, E. Narisano. - In: JOURNAL OF THE CHEMICAL SOCIETY. PERKIN TRANSACTIONS. I. - ISSN 0300-922X. - (1981), pp. 1278-1283.
Chiral acyl anion and enolonium ion equivalents. Asymmetric synthesis of α-methoxy-aldehydes
C.M.A. Gennari;C. Scolastico;
1981
Abstract
The reaction of the lithium derivative of (+)-(S)-p-tolyl p-tolylthiomethyl sulphoxide [(+)-(S)-(1)] with benzaldehyde and phenylacetaldehyde in tetrahydrofuran at -78 °C gives, after methylation of the hydroxy-group, reduction of the sulphoxide, and hydrolysis of the resulting dithioacetal, the corresponding α-methoxy-aldehydes, (-)-(R)-2-methoxy-2-phenylacetaldehyde and (+)-(R)-2-methoxy-3-phenylpropionaldehyde, enantiomeric excess 70 and 46%, respectively. The reaction of (+)-(S)-(1) with benzaldehyde in tetrahydrofuran at room temperature in the presence of Triton B gives the new optically pure reagent (E)-(+)-(S)-1-p-tolysulphinyl-1-p-tolylthio-2-phenylethylene [(+)-(S)-(2)], which is a chiral enolonium equivalent. The addition of sodium methoxide to (+)-(S)-(2) in methanol gives, after reduction of the sulphoxide and hydrolysis of the resulting dithioacetal, (+)-(S)-2-methoxy-2- phenylacetaldehyde, enantiomeric excess 60%. The unfavourable equilibrium in addition of methoxide to (+)-(S)-(2) means that the latter is not very useful as a chiral enolonium equilvalent in reactions of this type.Pubblicazioni consigliate
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