The conversion of esters to amides using aminomagnesium halides (Bodroux reaction) requires use of a two-fold excess of the nucleophile to provide good yields of amide.  Bassett and Thomas (J. Chem. Soc. 1954 , 1188) demonstrated reaction of equimolar amounts of methyl benzoate and anilinomagnesium iodide in diethyl ether yields a solid with composition consistent with the addition compound, and that treatment of this solid with a second equivalent of PhNHMgI provided much greater yields of amide (87% vs. 32%), suggesting that the second equivalent of reagent is required for productive breakdown of the intermediate.  They also demonstrated that in diethyl ether, sequential addition of equimolar quantities of PhNHMgI and Ph2NMgI yielded only the amide formed from the first aminomagnesium halide added.  We find quite different results when the reaction is of methyl benzoate with anilinomagnesium bromide is conducted in tetrahydrofuran: (1) the putative addition compound has sufficient solubility in THF such that no solid intermediate is formed,  and (2) when PhNHMgBr and Ph2NMgBr are added sequentially, N-phenylbenzamide is formed exclusively regardless of which aminomagnesium bromide is added first.  We now report the results of a series of competition experiments wherein methyl benzoate was allowed to react simultaneously with two anilinomagnesium bromides, including those of aniline, N-methylaniline, diphenylamine, and various phenyl-substituted anilines and N-methylanilines.  The Hammett plot of the relative rates of reaction for N-methylanilines shows a moderate negative slope (? = -0.18), reflecting the nucleophilicity of the aniline reagent in the addition step of the reaction.  On the other hand, reactions anilinomagnesium reagents prepared from phenyl-substituted anilines give a Hammett plot with a positive slope (? = 0.36), suggesting that based-promoted decomposition of the tetrahedral intermediate is a kinetically significant step in the reaction mechanism.

Studies of the reactivity of anilinomagnesium halides with esters

247th National Meeting (2014)

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