Diazo-thioketone coupling
| Barton–Kellogg reaction | |
|---|---|
| Named after |
Sir Derek Barton Richard M. Kellogg |
| Reaction type | Coupling reaction |
| Identifiers | |
| RSC ontology ID | RXNO:0000495 |
The Barton–Kellogg reaction is a coupling reaction between a diazo compound and a thioketone through a diazo intermediate forming an alkene. The Barton–Kellogg reaction is also known as Barton–Kellogg olefination and Barton olefin synthesis.
This reaction was pioneered by Hermann Staudinger, and the reaction also goes by the name Staudinger type diazo-thioketone coupling.
In the reaction mechanism for this reaction the diazo compound is a 1,3-dipole which reacts with the thioketone in a 1,3-dipolar cycloaddition to a thiadiazoline. This intermediate is unstable and through nitrogen gas expulsion and formation of an intermediate thiocarbonyl ylide it forms a stable episulfide. Triphenylphosphine opens the three-membered ring and then forms a sulfaphosphatane in a manner similar to the Wittig reaction. In the final step triphenylphosphine sulfide is expulsed liberating the alkene.
The diazo compound can be obtained from a ketone by reaction with hydrazine to a hydrazone followed by oxidation. Many reagents exist for this conversion for example silver(I) oxide and (bis(trifluoroacetoxy)iodo)benzene. The thioketone required for this reaction can be obtained from a ketone and phosphorus pentasulfide. Desulfurization of the episulfide can be accomplished by many phosphines and also by copper powder.
...
Wikipedia