In this work, we used experiments and density functional theory calculations to investigate the mechanism and driving forces of the reductive fragmentation of NHPI esters. Mechanistic studies suggest that the fragmentation behavior of the NHPI ester is influenced not only by the electronic nature of the substituent group but also by the stability of the radical intermediate. To further investigate this transformation, we next examined the aminoalkoxycarbonylation of alkenes using alkyl N-phthalimidoyl oxalates. With this approach, a variety of β-amino acid derivatives with diverse structures can be obtained in moderate to high yields.