Ethyl 4-bromobutyrate has been used as a building block for the synthesis of firefly luciferase inhibitor-conjugated peptide derivatives, and as a reagent for poly(2,6-dimethyl-1,4-phenylene oxide) and thieno[2,3-b]-azepin-4-ones synthesis. Ethyl 4-bromobutyrate has been used as a building block for the synthesis of firefly luciferase inhibitor-conjugated peptide derivatives, and as a reagent for poly(2,6-dimethyl-1,4-phenylene oxide) and thieno[2,3-b]-azepin-4-ones synthesis. A versatile building block and synthesis reagent