Kauffmann olefination

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The Kauffmann olefination is a chemical reaction to convert aldehydes and ketones to olefins with a terminal methylene group. This reaction was discovered by the German chemist Thomas Kauffmann and is related to the better known Tebbe olefination or Wittig reaction.

Formation of the reagent[edit]

The reagent was generated in situ by conversion of different halogenides of molybdenum or tungsten with methyllithium at low temperatures (−78 °C).[1][2][3][4]

Kauffmann olefination-reagent synthesis.svg

During the warm-up process the formation of the active reagent occurs. nmr-experiments has shown that the active reagent is not a Schrock carbene (e.g. Tebbe-reagent).

Mechanism[edit]

Mechanism experiments shows that the olefination process is a sequence of cycloaddition and cycloelimination steps.

Kauffmann mechanismus.png

Applications[edit]

For a long time this reaction had no applications in the synthetic organic chemistry. In 2002 it was used in a total synthesis of the terpene gleenol as a mild and non-basic reagent.[5] An one-pot-protocol with an olefin metathesis step with Grubbs catalyst is also available.[6] It is remarkable that the organometallic catalyst tolerates the inorganic reaction products.

References[edit]

  1. ^ T. Kauffmann, M. Papenberg, R. Wieschollek, J. Sander (1992). "Organomolybdän- und Organowolfram-Reagenzien, II. über den carbonylolefinierenden μ-Methylenkomplex aus Mo2Cl10 und vier äquivalenten Methyllithium". Chem. Ber. 125: 143–148. doi:10.1002/cber.19921250123. 
  2. ^ T. Kauffmann, P. Fiegenbaum, M. Papenberg, R. Wieschollek, D. Wingbermühl (1993). "Organomolybdän- und Organowolfram-;Reagenzien, III. Chemoselektive, nichtbasische Carbonylmethylenierungs-;Reagenzien aus MoOCl3(THF)2 und MoOCl4: Bildung, Thermolabilität, Struktur". Chem. Ber. 126: 79–87. doi:10.1002/cber.19931260114. 
  3. ^ T. Kauffmann, J. Braune, P. Fiegenbaum, U. Hansmersmann, C. Neiteler, M. Papenberg, R. Wiescholleck (1993). "Organomolybdän- und Organowolfram-;Reagenzien, IV. über die Chemoselektivität des carbonylmethylenierenden Reagenzes aus 2 MoOCl3(THF)2 und 4 CH3Li". Chem. Ber. 126: 89–96. doi:10.1002/cber.19931260115. 
  4. ^ T. Kauffmann (1997). "Neue Reaktionen molybdän- und wolframorganischer Verbindungen: Additiv-reduktive Carbonyldimerisierung, spontane Umwandlung von Methyl- in μ-Methylenliganden und selektive Carbonylmethylenierung". Angew. Chem. 109 (12): 1312–1329. doi:10.1002/ange.19971091205. 
  5. ^ K. Oesterreich, D. Spitzner (2002). "Short total synthesis of the spiro[4.5]decane sesquiterpene (−)-gleenol". Tetrahedron 58 (21): 4331–4334. doi:10.1016/S0040-4020(02)00336-8. 
  6. ^ K. Oesterreich, I. Klein, D. Spitzner (2002). Synlett: 1712–1714.