Isoindoline hydrochloride is an organic salt consisting of the saturated heterocyclic isoindoline core, which is a bicyclic structure containing a benzene ring fused with a five-membered nitrogen-containing ring, in its protonated hydrochloride form. It serves as a versatile and important synthetic building block in medicinal chemistry. Its primary application is as a key intermediate in the synthesis of various pharmacologically active compounds. The isoindoline scaffold is a privileged structure found in molecules targeting a range of therapeutic areas, including central nervous system disorders and oncology. It is frequently utilized to construct more complex heterocyclic systems or incorporated directly into drug candidates to modulate their physicochemical and binding properties. As a secondary amine salt, it offers improved stability and handling compared to the free base. Its reactivity makes it valuable for constructing amide bonds or for further functionalization of the nitrogen atom, enabling the rapid generation of diverse chemical libraries for drug discovery programs.