Syn-anti isomerization of aldols by enolization

The Journal of Organic Chemistry
Dale E WardP K Sasmal

Abstract

A variety of aldol adducts are shown to undergo efficient syn-anti isomerization in the presence of imidazole by an enolization mechanism. Isomerizations are high yielding and occur with little or none of the usual byproducts arising from competing elimination or retroaldol reactions. Most substrates reach equilibrium within 0.3-3 days at ambient temperature in chloroform, benzene, or dichloromethane containing 0.3-1 M imidazole. The process is particularly facile for aldols derived from tetrahydro-4H-thiopyran-4-one with rate constants for equilibration varying over ca. 1 order of magnitude for the adducts studied; structurally related aldols derived from cyclohexanone isomerized ca. 3-4 times slower. Isomerization of the acyclic aldol 5-hydroxy-4-methyl-5-phenyl-3-pentanone required heating to 60 degrees C but was achieved with minimal (<5%) retroaldol or elimination. A methoxymethyl ether derivative isomerized 30-40 times slower than the parent aldol. Isomerization of alpha,alpha'-disubstituted aldols and alpha,alpha'-bisaldols indicated low regioselectivity in the enolization. The synthetic utility of the process was demonstrated with the effective preparation of aldol stereoisomers unobtainable by direct methods.

References

Apr 25, 2000·Angewandte Chemie·T D Machajewski, C H Wong
Sep 13, 2001·Journal of the American Chemical Society·M KitamuraR Noyori
Dec 26, 2001·Chemical Reviews·R Mahrwald
Feb 2, 2002·Chemistry : a European Journal·Claudio PalomoJesús M García
Jun 13, 2002·Journal of the American Chemical Society·Karl A ScheidtWilliam R Roush
Feb 10, 2004·Chemical Society Reviews·Claudio PalomoJesús M García

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Citations

Dec 6, 2012·Organic Letters·Dale E Ward, M Mehdi Zahedi
Aug 27, 2005·Photochemical & Photobiological Sciences : Official Journal of the European Photochemistry Association and the European Society for Photobiology·M A van der HorstK J Hellingwerf
Aug 9, 2008·Chemical Communications : Chem Comm·Mohamed Amedjkouh, Maria Brandberg
Jul 16, 2011·Chemical Communications : Chem Comm·Dale E Ward
Feb 18, 2016·Chemical Reviews·Liang HongRui Wang
Apr 24, 2007·Angewandte Chemie·Naoto UtsumiCarlos F Barbas
Jan 16, 2010·Chemistry : a European Journal·Charles FehrJean-Yves de Saint Laumer
Nov 26, 2010·Chemistry : a European Journal·Jörg Pietruszka, Robert Christian Simon
Jan 9, 2008·The Journal of Organic Chemistry·Bernd SchetterRainer Mahrwald
May 20, 2009·The Journal of Organic Chemistry·Dale E WardM Mehdi Zahedi
Jan 26, 2006·Journal of the American Chemical Society·Susumu MitsumoriCarlos F Barbas

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