Prepn from picrocrocin: Kuhn, Winterstein, Ber. 67, 354 (1934). Synthesis: Kuhn, Wendt, Ber. 69, 1549 (1936); K"onst et al., Tetrahedron Lett. 1974, 3175. Biogenetic synthesis: T. Kametani et al., Chem. Pharm. Bull. 29,105 (1981).