(3aR,6aR)-4-benzyl-5-thioxohexahydro-2H-furo[3,2-b]pyrrol-2-one 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.