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

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. A weak base mediated spontaneous transformation of the active esters of N -protected ( E )-α,β-unsaturated γ-amino acids into N -protected ( Z )-α,β-unsaturated γ-lactams is described.