Insights into the Cerium Chloride‐Catalyzed Grignard Addition to Esters

Addition of methylmagnesium chloride to ester 1 in the presence of cerium chloride gave significantly better yields of the tertiary alcohol 2 than the reaction performed in the absence of cerium chloride. The beneficial effect of added cerium chloride is postulated to be due to suppression of the enolization of the ketone intermediate. The use of properly “activated” anhydrous cerium chloride which is proposed to generate a less basic, more nucleophilic species to overcome this undesired reaction was found to be critical. The activated cerium chloride was identified as the known seven‐coordinate THF solvate, [CeCl(μ‐Cl)₂(THF)₂]_n. Inactive crystal forms were also identified and the key parameters for formation of the active form were delineated.