In organic chemistry, the Doering–LaFlamme allene synthesis is a reaction of alkenes that converts them to allenes by insertion of a carbon atom. This name reaction is named for William von Eggers Doering 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 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 converts the dihalogenated carbon to a carbene or carbenoid-like structure. The resulting cyclopropylcarbene rearranges to form the allene product. The electronic nature of the carbene intermediate is not entirely understood. Several different mechanisms for its electrocyclic rearrangement have been studied.