New Approach to the Mechanism of the Reaction between Benzyl Grignard Reagents and Carbonyl Compounds

Article abstract of DOI:10.1021/jo00342a018

The reaction of the <(1-naphthyl)methyl>magnesium chloride with ketones can lead to the formation of ortho alcohols 4, normal alcohols 3, or enolates.We propose a mechanism for the reaction whose first step, as in the case of aldehydes, is a reversible attack of the ketone at the ortho position of the benzylic Grignard reagent, which can then lead to the formation of the normal alcohol and/or enolate.The fact that benzylmagnesium chloride reacts with cyclobutanone to give a diol analogous to that obtained in reactions with aldehydes, while its reaction with 1,1,1-trifluoro-2-propanone does not give a diol, leads us to propose an interpretation involving steric effects in the rearrangement alkoxide.In the case of ketones, these steric interactions generally prevent the Prins-type reaction leading to diols.