4-Aminophthalide is an organic compound featuring a phthalide (isobenzofuran-1(3H)-one) core structure substituted with an amino group at the 4-position. It is a white to off-white crystalline powder. This compound serves as a crucial synthetic intermediate in medicinal chemistry. Its primary application is in the synthesis of various biologically active molecules, particularly as a key building block for the production of certain pharmaceutical agents. For example, it is a known precursor in the synthesis of the anticonvulsant drug Brivaracetam and other related compounds targeting the central nervous system. The amino group and the reactive lactone moiety make it a versatile scaffold for constructing more complex heterocyclic systems. As a bifunctional molecule containing both an amine and a lactone, it is also utilized in organic synthesis research for constructing fused-ring systems and as a starting material for the development of novel chemical entities.