6-Hydroxyquinolin-2-one (I) was O-alkylated with 2-bromoacetophenone (II) by means of K2CO3 to give the phenacyl ether (III). Then, a Reformatsky-type condensation of (III) with ethyl 2-(bromomethyl)acrylate (IV) and Zn, with concomitant cyclization, yielded the target methylenebutyrolactone.