Enantioselective Cathodic Hydrogenation of Prostereogenic Activated Double Bonds
4-Methylcoumarine (1) is enantioselectively reduced in the presence of yohimbine at pH = 3 to afford 4-methyldihydrocoumarine (2) in 61% yield and nearly 70% ee. With 3-methylindenone and strychnine the dihydroproduct is formed with up to 36% ee. The role of the alkaloids is to catalyze the tautomerization of an intermediate enol radical and to enantioselectively protonate a ketoanion.
KeywordsQuantum Chemical Calculation Aqueous Methanol Enantiomeric Excess Cathodic Reduction Aqueous Methanol Solution
Unable to display preview. Download preview PDF.
- L. Horner in Organic Electrochemistry, 2. ed. Eds. H. Lund, M.M. Baizer, 1983, 945;Google Scholar
- [a]N. Schoo, H.J. Schäfer, Liebigs Ann. Chem. 1993, 601–607;Google Scholar
- [b]U. Höweler, N. Schoo, H.J. Schäfer, Liebigs Ann. Chem. 1993, 609–614;Google Scholar
- [c]M.F. Nielsen, B. Batanero, T. Löhl, H.J. Schäfer, E.-U. Wörthwein, R. Fröhlich, Chemistry,in press.Google Scholar
- R.N. Gourley, J. Grimshaw, P.G. Millar, J. Chem. Soc. (C) 1970, 2318–2323.Google Scholar
- T. Osa, V. Kashiwagi, Y. Yanagisawa, J. Bobbit, J. Chem. Soc. Chem. Commun. 1996, 2535–2537.Google Scholar