The first step involves extending the conjugation of the enone function by an additional double bond. Chloranil (tetrachloroquinone) is the forerunner of dichlorodicyanoquinone (DDQ), a reagent used extensively for introducing additional unsaturation in the progestin and corticoid series. In the case at hand, heating acetate with chloranil gives the diene, and reaction of that compound with methylmagnesium bromide in the presence of cuprous chloride leads to addition of the methyl group to position 7 at the end of the conjugated system. The stereochemistry of the product again illustrates the preference for additions from the backside. The alcohol at C17 is then oxidized to a ketone. Enamines are commonly used to activate adjacent functions; they are also not infrequently used, as in this case, as protecting groups. Thus, reaction of the intermediatewith pyrrolidine gives enamine. This transformation emphasizes the clear difference in reactivity between ketones at C7 and C17. A second methyl Grignard addition gives the corresponding 17a-methyl derivative. Hydrolysis of the enamine function then affords mibolerone.
^Murthy LR, Johnson MP, Rowley DR, Young CY, Scardino PT, Tindall DJ (1986). "Characterization of steroid receptors in human prostate using mibolerone". Prostate8 (3): 241–53. doi:10.1002/pros.2990080305. PMID2422638.