Studies on the grignard reaction. IX. Autocatalytic aspects of the reaction on ketones

In the Grignard reaction, magnesium bromide and alcoholates (e.g. reaction products) greatly reduce the reaction velocity of either the addition or the reduction with ketones. Magnesium bromide and α‐unbranched alcoholates favour however the addition over the reduction reaction. Complex (α‐branched) alcoholates on the contrary favour reduction, and this can be prevented by adding magnesium bromide. The mechanism proposed by Hamelin (14) can be adopted by supposing a nucleophilic attack of the Grignard reagent on the ketone, assisted by ketone/magnesium bromide or ketone/alcoholate complexation.