Kauffmann olefination

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

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]

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

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

Applications

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

  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). "'One-pot' Reactions: Total Synthesis of the Spirocyclic Marine Sesquiterpene, (+)-Axenol". Synlett: 1712–1714. doi:10.1055/s-2002-34211.
This article is issued from Wikipedia - version of the 6/1/2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.