By the use of pyrophosphoryl chloride, 21-hydroxy-20-oxosteroids were phosphorylated in one step in quantitative yield. When the reaction was carried out on prednisolone at a higher temperature, a dienonephenol rearrangement and a simultaneous pinacolic shift took place resulting in the formation of 3, 21-diphosphate of C-nor-9, 10-secosteroidal aldehyde (A) as a by-product. This compound showed a cardioinhibitory and vasoconstricting activity and a strong toxicity to rabbits.