The acidity of carboxylic acids and 1º & 2º-amides acts to convert Grignard and alkyl lithium reagents to hydrocarbons (see equations), so these functional groups should be avoided when these reagents are used.

What do Grignards react with?

Grignard reagents are formed by the reaction of magnesium metal with alkyl or alkenyl halides. They're extremely good nucleophiles, reacting with electrophiles such as carbonyl compounds (aldehydes, ketones, esters, carbon dioxide, etc) and epoxides.

What happens when Grignard reagent reacts with amide?

For a N,N-alkyl, a N,N-diaryl or a N-alkyl-N-aryl amide that what will happen is that the grignard will react attacking the carbonyl carbon. This will form R''C(NR2)(R')-OMgX from RMgX and R''-CONR2.