Ethyl (2E,4S)-4,5-isopropylidenedioxy-2-methylpent-2-enoate can be used for the synthesis of 2'-deoxy-2'-fluoro-2'-C-methylcytidine (I) (PSI-6130), which is a potent and selective inhibitor of HCV NS5B polymerase and marine dolabellane diterpenoids (ie. claenone (I), palominol (II), and dolabellatrienone (III)). It also has potential applications for the synthesis of related antiviral agents. Molecular Formula: C11H18O4 Molecular Weight: 214.26