(3aR-?cis)?-Hexahydro-?2-?oxo-4H-?furo[3,?2-?b]?pyrrole-?4-?acetic Acid Ethyl Ester is an intermediate in synthesizing Monocrotaline-d4 (M526002), a labelled Monocrotaline (M526000) which is a toxic pyrrolizidine alkaloid isolated from Crotalaria spp. It is used for inducing pulmonary diseases in rats.