Process for preparing elagolix sodium and intermediates thereof

A process for preparing elagolix of formula I:

• or a pharmaceutically acceptable salt thereof, the process comprising:
• 1) contacting a compound of formula V:
• with a compound of formula IV:
• and one or more coupling agents in a first solvent to form a mixture;
• 2) treating the mixture with an acid and neutralizing to provide a compound of formula VII:
• 3) contacting the compound of formula VII with ethyl 4-halobutyrate and a third base in a fourth solvent to form a compound of formula VIII:
• and
• 4) treating the compound of formula VIII with a fourth base in a fifth solvent to provide elagolix of formula I or the pharmaceutically acceptable salt thereof,
• wherein R1 is hydrogen, methanesulfonate, or p-toluenesulfonate;
• and
• R2 and R3 are independently hydrogen, substituted or unsubstituted C1-8 alkyl, or substituted or unsubstituted C6-12 aryl.