N-methyl-2-pyrrolidone → Naltrexone

Participants

Reaction Conditions

Reaction Steps

Naltrexone was prepared in high yield by direct N-alkylation of noroxymorphone with an alkyl halide in the presence of a protic solvent. Accordingly, 5.5 g of noroxymorphone, 16.5 mL of N-methyl-2-pyrrolidinone (NMP), and 1.65 mL of water were added to a flask (100 mL, 3 necked). The flask was flushed with nitrogen, and the reaction mixture was kept under nitrogen throughout the reaction. Next, 2.4 mL of bromomethylcyclopropane and 2.5 mL of triethylamine (NEt3) were added to the flask, which was then heated at 70° C. for 2 h. An additional 2.5 mL of NEt3 was added to the flask, and the mixture was heated at 70° C. for 7.5 h. HPLC analysis revealed that the reaction is completed with noroxymorphone at less than two percent or one percent and undesired side products such as quaternary ammonium salt and O-alkylation of phenol group were present at less than two percent or were undetectable. The mixture was cooled to room temperature, and water (82.5 g) was added to give a precipitate. The mixture was stirred for 1 h and then filtered. The solid was washed with water (2×5.5 mL) and dried under vacuum at 65° C. for 18 h to give 5.68 g of naltrexone as solid.

Provenance & Evidence