Abstract Hydrogenation of the ketone group in di-O-benzylderivative (8) of the known macrocyclic lactone zeralenone (7) using a novel chiral borane complex 3. BH 3, prepared in situ, proceeded at lower temperatures with moderate diastereoselectivity (∼ 40%, de at− 60). Unsaturated diastereomers 9 and 10 were separated, and 9 converted into zeranol (11), a known anabolic agent. Restricted conformational mobility at lower temperatures is ...