Similarly to an enolate anion, the α carbon of an enamine is nucleophilic. It can also be used to react by nucleophilic substitution with alkyl halides. Although having an enamine reaction such as this on the MCAT might be a bit harder than expected, I would not put it past them because of the significance of aldehyde and ketone chemistry for the exam. Enamines are important aldehyde/ketone derivatives.