1962, James A. Moore, Erich Heftmann, Chapter 2: Chemistry of the adrenocortical steroids, Helen Wendler Deane, The Adrenocortical Hormones, Part 1, Springer-Verlag, page 221, The 21-hydroxyl group in the α-ketol side chain is very easily esterified, and in many of the synthetic routes leading to these side chains the ketol acetate is still formed.
Source: wiktionary