The Barbier Synthesis: A One-Step Grignard Reaction?

Article abstract of DOI:10.1021/ja00376a039

Counter to generally accepted theory, it is demonstrated that the Byrbier synthesis does not necessarily involve the in situ formation of an organometallic compound.In certain cases, there is a radical pathway in which the anion radical (R^.-X^-) resulting from the attack by a halogenated derivative on lithium is directly trapped by the ketone or by the ketyl radical on the metal surface befor the organometallic compound forms.This pathway can be unique, as when 1-bromoadamantane condenses with adamantanone or hexamethylacetone.However, by extension of the Barbier synthesis to other "cage-structure" compounds homologous to adamantane, it is seen that the radical pathway can compete with the organometallic pathway and that this competition is principally determined by the stability of the cage radicals generated at the metal-solution interface.An optimum yield can be attained in this type of synthesis by choosing the Grignard reaction or the Barbier reaction, depending on the nature of the halogenated cage derivatives in use.