Used as a key intermediate in the synthesis of biologically active compounds, particularly in pharmaceuticals and agrochemicals. Its sulfonyl chloride group readily reacts with amines and alcohols, making it valuable for constructing sulfonamide and sulfonate ester derivatives. Commonly employed in the development of kinase inhibitors and other targeted therapies in medicinal chemistry. Also utilized in the preparation of fluorescent probes and dyes due to the isoquinoline core’s favorable photophysical properties. Its chloro substituents allow for further functionalization via cross-coupling reactions, enhancing its utility in complex molecule assembly.