Abstract: The chemoselective reduction of 21-azidocorticosteroids to the corresponding 21-primary aminocorticosteroids was achieved with Zn/NH₄Cl as a reductant in reasonable yields(70%—85%). 11β-Hydroxyl-21-azidocorticosteroids were found to be easier to reduced to their amino counterparts more easily than 11-carbonyl and 11-deoxyl-21-azides. Aqueous THF was found to be the most suitable solvent for this reaction, and the ratio of water in the reducing system was crucial. In THF of 95%—97% in volume fraction and at 15 ℃, Zn/NH₄Cl can only reduce 11β-hydroxyl-21-azidocorticosteroids. To reduce the 11-carbonyl and 11-deoxy-21-azides, the volume fraction of water should be raised to 10% at least. This reduction method hasthe advantages of rather mild conditions, cheap and easily accessible reagents, and reasonable overall yields. Moreover, its simple work up and easy manipulation in large scale make our method superior to the reported Gabriel and 21-aldehyde oxime reduction procedures in the literature.

Key words: Zinc/ammonium chloride, 21-Azidocorticoids, 21-Primary aminocorticoids, Chemoselective reduction