One of the easiest methods of forming azomethine ylides is by condensation of an aldehyde with an amine. If the amine contains an electron-withdrawing group on the alpha carbon, such as an ester, the deprotonation occurs readily. A possible disadvantage of using this method is that the ester ends up in the cycloaddition product. An alternative is to use a carboxylic acid, which can easily be removed during the cycloaddition process by decarboxylation.