Hydroboration of unsaturated fatty acid methyl esters and conversion of the boron adducts*

Authors

  • Theodor Lucas,

    1. Westfälische Wilhelms-Universität, Organisch-Chemisches Institut, Münster, Germany
    Search for more papers by this author
    • Current address: Covance Laboratories GmbH, Kesselfeld 29, 48163 Münster, Germany.
  • Hans J. Schäfer

    Corresponding author
    1. Westfälische Wilhelms-Universität, Organisch-Chemisches Institut, Münster, Germany
    • Correspondence: Professor Hans J. Schäfer, Westfälische Wilhelms-Universität, Organisch-Chemisches Institut, Correns-Strasse 40, 48149 Münster, Germany

      E-mail: schafeh@uni-muenster.de

      Fax: +49 251 8336523

    Search for more papers by this author

  • Dedicated to Professor Dr. Peter Metz (TU Dresden) on the occasion of his 60th birthday.

Abstract

Unsaturated FAMEs can be modified to higher value compounds by hydroboration of the double bond. The added boron atom can be replaced in a subsequent oxidation by a hydroxy group. This way methyl 10-undecenoate (1b), methyl oleate (3a), methyl ricinoleate ((9Z,12R)-6a), and methyl linoleate (9) were converted into methyl 11-hydroxyundecanoate and methyl hydroxyoctadecanoates in 82–92% yield. Organoboranes isomerize at higher temperatures. Hydroboration of oleic acid and subsequent heating to 220°C led after oxidative work-up to 70% of 1,4-octadecanediol. Presumably a 1,4-oxaborinane intermediate is involved. Alkyl groups of organoboranes can be attached to the carbonyl-equivalent: dichloromethyl methyl ether (DCME). With this reaction the boranes of the esters 1b and 3a were converted in 55–80% yield to dimers with an inserted ketocarbonyl group. Ester 9 afforded in the same reaction methyl nonadecanoates with an integrated cyclopentene ring.

Practical applications: Hydroboration–oxidation allows the partially regioselective conversion of unsaturated FAMEs into hydroxy- and dihydroxyesters. Thermal isomerization of the boranes from methyl oleate, oleic acid, and oleyl alcohol leads after oxidative work-up to the 1,4-diol: 1,4-octadecanediol as main product. These products are useful as components for polyesters, polyurethanes, and precursors for heterocycles. Reaction of organoboranes from unsaturated FAMEs with the carbonyl equivalent: DCME provides a one-step access to 1,ω-diesters with an internal keto group, which can be applied for coupling, cross-linking, and further conversion. The borane · THF complex is commercially available in amounts of 0.8 mol and more to do exploratory research toward such applications.

Ancillary