Elagolix′s key intermediate 3-[ (2R)-2-Amino-2-phenylethyl]-5- (2-fluoro-3-methoxyphenyl)-1-[[2-fluoro-6- (trifluoromethyl)phenyl]methyl]-6-methyl-2, 4 (1H, 3H)-pyrimidinedione was synthesized from 5- (2-Fluoro-3-methoxyphenyl)-1-[2-fluoro-6- (trifluoromethyl)benzyl]-6-methyl-2, 4 (1H, 3H)-pyrimidinedione (Compound 1) and N-[ (1R)-2-[ (Methylsulfonyl)oxy]-1-phenylethyl] carbamic acid 1, 1-dimethylethyl ester (Compound 2) through ammonia alkylation under alk. conditions and deprotection reaction under acidic conditions.The above two steps were optimized and the optimal reaction conditions were determinedThe optimal conditions for the ammonia alkylation reaction were as follows: the catalyst was selected sodium bicarbonate, the molar ratio of compound 1: sodium bicarbonate was 1:2, and the reaction temperature was 50°C.The optimum conditions for the deprotective reaction were as follows:the catalyst was selected as concentrated hydrochloric acid and the molar ratio of N-[ (1R)-2-[5- (2-fluoro-3-methoxyphenyl)-3-[[2-fluoro-6- (trifluoromethyl) phenyl]methyl]-3, 6-dihydro-4-methyl-2, 6-dioxo-1 (2H)-pyrimidinyl]-1-phenylethyl]-1, 1-dimethylethyl ester (Compound 3):concentrated hydrochloric acid was 1:25.Under the above conditions, the total molar yield was 91.3% based on compound 1.