Reactions of Dialkylmagnesium-Salt Mixtures with Ketones: Increasing the Ratio of Addition to Reduction

Article abstract of DOI:10.1021/jo00297a055

The reduction of the ketone to a secondary alcohol that accompanies addition in reactions of ketones and dialkylmagnesium compounds can be lessened by first adding an appropriate salt to the dialkylmagnesium compound.With favorable salts and reactant stoichiometries, reduction is eliminated in reactions of dipropylmagnesium with diisopropyl ketone or di-tert-butyl ketone.In reactions of di-tert-butylmagnesium and di-tert-butyl ketone, reduction always predominates, although some addition does occur.Salts observed to have significant effects are potassium methoxide, (Me2NCH2)2CHOK, sodium methoxide, lithium methoxide, lithium tert-butoxide, tetrabutylammonium bromide, and benzyltriethylammonium chloride.Stoichiometry has significant effects on product composition, the least reduction product generally resulting when the ratio of salt to diorganomagnesium compound is at least one.The fundamental significance of the effects of stoichiometry and of the relative effects caused by different salts is obscured, however, by the heterogeneity of many of the systems.Magnesiate ions, such as (R2MgOMe)2 2-, are thought to be the organomagnesium species responsible for reactions that proceed without reduction.