It is sometimes called vitamin k3,although derivatives of naphthoquinone without the side chain in the 3-position cannot exert all the functions of the K Vitamins. Menadione is a vitamin precursor of K2 which utilizes alkylation to yield menaquinones (MK-n, n=1-13; K2 vitamers), and hence, is better classified as a provitamin.
It is also known as "menaphthone".