available andros-4-ene-3, 17-dione. The strategy is based on the use of K ¹³ CN for labeling
at position 20 and of ¹³ CH 3 MgI, generated in situ, for labeling at position 21. Because of
the early introduction of the [¹³ C] labeling, our efforts aimed at reproducible experimental
procedures giving high yields with respect to the isotope containing precursors. During the
development of this hemisynthesis, we noted that judicious choice of protective groups was …