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The reaction is a two-stage process, in which first the alkene is reacted with dichlorocarbene or 
organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, J.; ...
, the Doering–LaFlamme allene synthesis is a reaction of alkene
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...
s that converts them to allenes by insertion of a carbon atom. This name reaction is named for William von Eggers Doering
William von Eggers Doering (June 22, 1917 – January 3, 2011) was the Mallinckrodt Professor of Chemistry at Harvard University. Before Harvard, he taught at Columbia University, Columbia (1942–1952) and Yale (1952–1968).
Doering was born ...
and a co-worker, who first reported it.
The reaction is a two-stage process, in which first the alkene is reacted with dichlorocarbene or dibromocarbene
Dichlorocarbene is the reactive intermediate with chemical formula CCl2. Although this chemical species has not been isolated, it is a common intermediate in organic chemistry, being generated from chloroform. This bent diamagnetic molecule rapidly ...
to form a dihalocyclopropane. This intermediate is then reacted with a reducing metal, such as sodium or magnesium, or with an organolithium reagent. Either approach results in metal-halogen exchange to convert the ''gem''-dihalogenated carbon to a 1-metallo-1-halocyclopropane. This species undergoes α-elimination of metal halide and ring-opening via an electrocyclic reaction (at least formally) to give the allene. Several different mechanism
Mechanism may refer to:
*Mechanism (engineering), rigid bodies connected by joints in order to accomplish a desired force and/or motion transmission
*Mechanism (biology), explaining how a feature is created
*Mechanism (philosophy), a theory that a ...
s for the electrocyclic In organic chemistry, an electrocyclic reaction is a type of pericyclic reaction, pericyclic rearrangement reaction, rearrangement where the net result is one pi bond being converted into one sigma bond or vice versa. These reactions are usually cat ...
rearrangement have been studied.
In a study in which an enantioenriched substituted cyclopropyl Grignard reagent was prepared, the reaction was shown to give the allene with very high levels of enantiospecificity, suggesting a concerted mechanism. Similarly, in a computational study of the bromolithiocyclopropane, a concerted mechanism was found to be favored. A discrete cyclopropylidene carbene was found to be unlikely, although early ejection of LiBr (roughly simultaneous to C–C bond scission and before formation of the orthogonal pi bonds of the allene) was suggested.
References
{{DEFAULTSORT:Doering-LaFlamme allene synthesis Name reactions