Cyclization of N-Boc-(E)-α,β-unsaturated γ-amino acid active esters into N-Boc-(Z)-α,β-unsaturated γ-lactams through E → Z isomerization

Here, we are reporting the spontaneous transformation of the active esters of N-Boc protected E-alpha,beta-unsaturated gamma-amino acids into the corresponding Z-alpha,beta-unsaturated gamma-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 gamma-NH is crucial for both lactamization and E -> Z isomerization. This mild transformation provides easy access to the synthetically challenging alpha,beta-unsaturated gamma-lactams and also gives new insights into the E -> Z isomerization of double bonds.