Here, we are reporting the spontaneous transformation of the active esters of N-Boc protected E-α,β-unsaturated γ-amino acids into the corresponding Z-α,β-unsaturated γ-lactams with concomitant E → Z isomerization in the presence of a weak base. No cyclization was observed in the absence of the base. Analysis revealed that amide γ-NH is crucial for both lactamization and E → Z isomerization. This mild transformation provides easy access to the synthetically challenging α,β-unsaturated γ-lactams and also gives new insights into the E → Z isomerization of double bonds.