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]
![Kauffmann olefination-reagent synthesis.svg](http://upload.wikimedia.org/wikipedia/commons/thumb/d/d8/Kauffmann_olefination-reagent_synthesis.svg/600px-Kauffmann_olefination-reagent_synthesis.svg.png)
During the warm-up process the formation of the active reagent occurs. NMR-experiments have 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.
![Kauffmann mechanismus.png](http://upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Kauffmann_mechanismus.png/600px-Kauffmann_mechanismus.png)
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 as a mild and non-basic reagent.[5] A 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[]
- ^ 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.
- ^ 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.
- ^ T. Kauffmann; J. Baune; 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.
- ^ 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.
- ^ 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.
- ^ K. Oesterreich; I. Klein; D. Spitzner (2002). "'One-pot' Reactions: Total Synthesis of the Spirocyclic Marine Sesquiterpene, (+)-Axenol". Synlett (10): 1712–1714. doi:10.1055/s-2002-34211.
- Name reactions
- Carbon-carbon bond forming reactions
- Olefination reactions