Petasis reagent
Encyclopedia
The Petasis reagent is dimethyl titanocene, Cp2TiMe2, readily prepared by the reaction of methylmagnesium chloride
or methyllithium with titanocene dichloride
:
It is used for transforming carbonyl groups to terminal alkenes, much like the Tebbe reagent or Wittig reaction
. Unlike the Wittig reaction, the Petasis reagent can react with a wide range of carbonyls, including aldehydes, ketones and esters. The Petasis reagent is also more air stable than the Tebbe reagent, and can be isolated as a pure solid, or used directly as a solution in toluene-THF.
The active olefinating reagent, Cp2TiCH2, is prepared by heating the Petasis reagent in toluene or THF to 60 °C.
The reaction mechanism is very similar to that of the Tebbe reagent, first yielding a titanium carbene
which forms a four membered oxatitanacyclobutane and than releases the terminal alkene.
Methylmagnesium chloride
Methylmagnesium chloride is a commercially available Grignard reagent. Like methyllithium, it is the synthetic equivalent to the methyl carbanion synthon. It is usually sold as a solution in tetrahydrofuran. The model of the molecule shows methylmagnesium chloride with the magnesium atom in the...
or methyllithium with titanocene dichloride
Titanocene dichloride
Titanocene dichloride is the organotitanium compound with the formula 2TiCl2, commonly abbreviated as Cp2TiCl2. This metallocene is a common reagent in organometallic and organic synthesis. It exists as a bright red solid that slowly hydrolyzes in air...
:
- Cp2TiCl2 + 2 "Me−" → Cp2TiMe2 + 2 Cl−
It is used for transforming carbonyl groups to terminal alkenes, much like the Tebbe reagent or 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....
. Unlike the Wittig reaction, the Petasis reagent can react with a wide range of carbonyls, including aldehydes, ketones and esters. The Petasis reagent is also more air stable than the Tebbe reagent, and can be isolated as a pure solid, or used directly as a solution in toluene-THF.
The active olefinating reagent, Cp2TiCH2, is prepared by heating the Petasis reagent in toluene or THF to 60 °C.
The reaction mechanism is very similar to that of the Tebbe reagent, first yielding a titanium carbene
Carbene
In chemistry, a carbene is a molecule containing a neutral carbon atom with a valence of two and two unshared valence electrons. The general formula is RR'C:, but the carbon can instead be double-bonded to one group. The term "carbene" may also merely refer to the compound H2C:, also called...
which forms a four membered oxatitanacyclobutane and than releases the terminal alkene.