(13α,?14α)?-14,?19-?Dihydro-?12,?13-?[methylenebis(oxy)?]?-?20-?norcrotalanan-?11,?15-?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.