A quantum-chemical simulation by MNDO method of probable migration mechanisms of proton and methoxycarbonyl group in a series of amidinylcyclopentadiene derivatives taking in consideration methoxycarbonyl and aryl substituents attached respectively to the cyclopentadienyl and amidine moieties provided a theoretical confirmation of 1,4-shift occurrence for the methoxycarbonyl group in quantitative agreement with the experimental evaluation of the barrier in this reaction.