5-Vinylbenzofuran

5-Vinylbenzofuran is a benzofuran derivative featuring a five-membered furan ring fused to a benzene ring, with a vinyl substituent at the 5-position. This compound serves as a critical process-related impurity in the synthesis of Darifenacin, arising from incomplete cyclization or side-chain coupling during API manufacturing. Its unsaturated side chain introduces conjugation effects influencing chromatographic behavior. Structurally, it lacks the piperidine moiety of Darifenacin, differing by a single ethylenic substitution. Analytically, it functions as an HPLC reference standard for quantifying impurity levels in Darifenacin drug substance.