β-Functionalized α,β-unsaturated amino acids were synthesized by an addition-elimination pathway. Reaction of methyl β-bromo-α-formylaminoacrylates (3a-e), which were prepared by the condensation of methyl isocyanoacetate (1) with aldehydes followed by bromination, with thiols gave β-alkylthio-α, β-unsaturated amino acidderivatives (6a-f). The reaction of (3a) with sodium azide resulted in the formation