Methyl 4-bromo-2-butenoate is an organic compound featuring both an α,β-unsaturated ester moiety and an allylic bromide functional group. This bifunctional structure makes it a versatile and reactive building block in synthetic organic chemistry. Its primary application is as a key intermediate in the synthesis of more complex molecules. The allylic bromide site is highly reactive in nucleophilic substitution reactions (e.g., SN2), allowing for the introduction of various nucleophiles. Simultaneously, the α,β-unsaturated ester is an excellent Michael acceptor, enabling conjugate addition reactions. This dual reactivity is exploited in multi-step syntheses, particularly for constructing carbon chains and heterocyclic systems. Due to its reactive nature, it should be handled with care under inert atmosphere and stored at low temperatures. It is a valuable reagent for academic and industrial research laboratories focused on developing new synthetic methodologies and preparing pharmaceutical or agrochemical intermediates.