Barton-Kellogg reaction
Encyclopedia
The Barton-Kellogg reaction is a coupling reaction
between a ketone
and a thioketone
through a diazo
intermediate forming an alkene
.
This reaction has been pioneered by Hermann Staudinger
and therefore the reaction also goes by the name Staudinger type diazo-thioketone coupling.
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 triphenylphosphinesulfoxide is expulsed liberating the alkene
.
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.
The main advantage of this reaction over the McMurry reaction
is the notion that the reaction can take place with two different ketones. In this regard the diazo-thioketone coupling is a cross-coupling rather than a homocoupling.
Coupling reaction
A coupling reaction in organic chemistry is a catch-all term for a variety of reactions where two hydrocarbon fragments are coupled with the aid of a metal catalyst...
between a ketone
Ketone
In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...
and a thioketone
Thioketone
Thioketones are organosulfur compounds related to conventional ketones. Instead of the formula R2C=O, thioketones have the formula R2C=S. Unhindered alkylthioketones are typically unstable; such compounds tend to form polymers or rings.-Preparative methods:Thiones are usually prepared from ketones...
through a diazo
Diazo
Diazo refers to a type of organic compound called diazo compound that has two linked nitrogen atoms as a terminal functional group. The general formula is R2C=N2. The simplest example of a diazo compound is diazomethane...
intermediate forming an alkene
Alkene
In organic chemistry, an alkene, olefin, or olefine is an unsaturated chemical compound containing at least one carbon-to-carbon double bond...
.
This reaction has been pioneered by Hermann Staudinger
Hermann Staudinger
- External links :* Staudinger's * Staudinger's Nobel Lecture *....
and therefore the reaction also goes by the name Staudinger type diazo-thioketone coupling.
Reaction mechanism
In the reaction mechanismReaction mechanism
In chemistry, a reaction mechanism is the step by step sequence of elementary reactions by which overall chemical change occurs.Although only the net chemical change is directly observable for most chemical reactions, experiments can often be designed that suggest the possible sequence of steps in...
for this reaction the diazo
Diazo
Diazo refers to a type of organic compound called diazo compound that has two linked nitrogen atoms as a terminal functional group. The general formula is R2C=N2. The simplest example of a diazo compound is diazomethane...
compound is a 1,3-dipole
1,3-dipole
In organic chemistry, a 1,3-dipolar compound or 1,3-dipole is a dipolar compound with delocalized electrons and a separation of charge over three atoms...
which reacts with the thioketone
Thioketone
Thioketones are organosulfur compounds related to conventional ketones. Instead of the formula R2C=O, thioketones have the formula R2C=S. Unhindered alkylthioketones are typically unstable; such compounds tend to form polymers or rings.-Preparative methods:Thiones are usually prepared from ketones...
in a 1,3-dipolar cycloaddition
1,3-dipolar cycloaddition
The 1,3-dipolar cycloaddition, also known as the Huisgen cycloaddition or Huisgen reaction, is an organic chemical reaction belonging to the larger class of concerted, pericyclic cycloadditions. It is the reaction between a 1,3-dipole and a dipolarophile, most of which are substituted alkenes, to...
to a thiadiazoline. This intermediate is unstable and through nitrogen gas expulsion and formation of an intermediate thiocarbonyl ylide it forms a stable episulfide
Episulfide
Episulfides are a class of organic compounds that contain a saturated heterocyclic ring consisting of two carbon atoms and one sulfur atom. It is the sulfur analogue of an epoxide or aziridine. They are also known as thiiranes, olefin sulfides, thioalkylene oxides, and thiacyclopropanes.The parent...
. Triphenylphosphine
Triphenylphosphine
Triphenylphosphine is a common organophosphorus compound with the formula P3 - often abbreviated to PPh3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists as relatively air stable, colorless crystals at room temperature...
opens the three-membered ring and then forms a sulfaphosphatane in a manner similar to the Wittig reaction
Wittig reaction
The Wittig reaction is a chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide to give an alkene and triphenylphosphine oxide....
. In the final step triphenylphosphinesulfoxide is expulsed liberating the alkene
Alkene
In organic chemistry, an alkene, olefin, or olefine is an unsaturated chemical compound containing at least one carbon-to-carbon double bond...
.
Scope
The diazo compound can be obtained from a ketoneKetone
In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...
by reaction with hydrazine
Hydrazine
Hydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...
to a hydrazone
Hydrazone
Hydrazones are a class of organic compounds with the structure R1R2C=NNH2. They are related to ketones and aldehydes by the replacement of the oxygen with the NNH2 functional group...
followed by oxidation. Many reagents exist for this conversion for example silver(I) oxide
Silver(I) oxide
Silver oxide is the chemical compound with the formula Ag2O. It is a fine black or dark brown powder that is used to prepare other silver compounds.-Preparation:...
and (bis(trifluoroacetoxy)iodo)benzene
(Bis(trifluoroacetoxy)iodo)benzene
benzene, C10H5F6IO4, is a hypervalent iodine compound used as a reagent in organic chemistry. The reagent is used in an acidic modification of the Hofmann rearrangement. One example is the conversion of cyclobutanecarboxamine to cyclobutylamine hydrochloride...
. The thioketone
Thioketone
Thioketones are organosulfur compounds related to conventional ketones. Instead of the formula R2C=O, thioketones have the formula R2C=S. Unhindered alkylthioketones are typically unstable; such compounds tend to form polymers or rings.-Preparative methods:Thiones are usually prepared from ketones...
required for this reaction can be obtained from a ketone and phosphorus pentasulfide
Phosphorus pentasulfide
Phosphorus pentasulfide is the inorganic compound with the formula P4S10. This yellow solid is the one of two phosphorus sulfides of commercial value...
. Desulfurization of the episulfide can be accomplished by many phosphines and also by copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
powder.
The main advantage of this reaction over the McMurry reaction
McMurry reaction
The McMurry reaction is an organic reaction in which two ketone or aldehyde groups are coupled to an alkene using titanium chloride compound such as titanium chloride and a reducing agent. The reaction is named after its co-discoverer, John E. McMurry. The McMurry reaction originally involved the...
is the notion that the reaction can take place with two different ketones. In this regard the diazo-thioketone coupling is a cross-coupling rather than a homocoupling.