(3aR,?6aR)?-Tetrahydro-?4-?[(4-?methoxyphenyl)?methyl]?-2H-?furo[3,?2-?b]?pyrrole-?2,?5(3H)?-?dione 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.