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.
This species undergoes α-elimination of metal halide and ring-opening via an electrocyclic reaction (at least formally) to give the allene.
[3] 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.
[4] Similarly, in a computational study of the bromolithiocyclopropane, a concerted mechanism was found to be favored.