Seyferth–Gilbert homologation

The Seyferth -Gilbert chain extension known as Seyferth -Gilbert or reaction Seyferth -Gilbert homologation reaction is a name of the organic chemistry. It was named after Dietmar Seyferth, who published them in 1970. In 1979, the reaction of John C. Gilbert et al. were studied in detail. Reacting an aldehyde or ketone to an internal or terminal alkynes in this reaction.

Survey

In the presence of potassium tert- butoxide and dimethyl ( diazomethyl ) phosphonate (also known as Gilbert - Seyferth reagent) reacting aldehydes and ketones to alkynes. This reaction is also homologation or chain extension called because R1 and R2 exactly one carbon atom ( in the overview highlighted in blue ) to the reaction between the residues is more than before.

If an aldehyde reactant used, one obtains a terminal alkyne ( 1-alkyne ). The starting material is a ketone (ie R1 ≠ R2 ≠ H ) to the C ≡ C- triple bond is located in the inner part of the molecule.

Mechanism

Tert- butoxide as the base and acts deprotonates the - Gilgert Seyferth reagent ( 1), so that a 2 carbanion is formed. The negatively charged carbon atom henceforth 2 engages at the carbonyl group of the aldehyde or the ketone, resulting in the formation of an alcoholate 3. The following is an intramolecular attack of the negatively charged oxygen 3 on the phosphorus atom. This approach fosters the ring closure Vierringintermediat 4 with elimination of a Dimethylphosphats an intermediate article in the form of a Diazovinylverbindung 5 For this intermediate splits from nitrogen and a carbene is formed 6 is followed by a rearrangement of the radical R 2 and thus the formation of an alkyne 7 as a product.

Bestmann modification

  • Dimethyl ( 1 -diazo -2- oxopropyl ) phosphonate according to IUPAC nomenclature
  • 1- Diazoacetonylphosphonsäuredimethylester
  • (1- Diazo -2- oxopropyl ) phosphonate
  • Dimethyl - 1 Diazoacetonylphosphonat
  • Ohira reagent

The Seyferth -Gilbert reaction was modified by Susumu Ohira and Hans Jürgen Bestmann. The generation of dimethyl ( diazomethyl ) phosphonate prepared in situ by the reaction of dimethyl ( 1 -diazo -2- oxopropyl ) phosphonate (also known as the Ohira- Bestmann reagent) with methanol and potassium carbonate ensures a high yield in the synthesis of terminal alkynes. R is here again an organic radical

One advantage of the Bestmann modification is that the reaction conditions are very mild and so many functional groups are tolerated.

Potassium tert-butoxide Base (chemistry) Protonation CAS registry number Wittig reaction Horner–Wadsworth–Emmons reaction Corey–Fuchs reaction Tetrahedron Letters Digital Object Identifier Journal of Organic Chemistry
157749
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