General procedure for the synthesis of vitamin K4 from 2-methyl-1,4-naphthoquinone (20.0 g) and acetic anhydride (29.65 g): 2-methyl-1,4-naphthoquinone was first dissolved in ethyl acetate (200 g). Subsequently, acetic anhydride, 4-dimethylaminopyridine (DMAP, 1.42 g), and palladium/carbon catalyst (Pd/C, 0.6 g) were added to the solution. The reaction mixture was stirred at room temperature in a hydrogen atmosphere overnight. Upon completion of the reaction, the Pd/C catalyst was removed by filtration. The filtrate was washed with brine and the organic layer was separated. The organic layer was concentrated and recrystallized in a solvent mixture of water (60 g) and isopropanol (IPA, 80 g) to yield 28.0 g of vitamin K4 as white crystals (yield: 84.2%, HPLC purity: 99.8%). The structure of the compound was characterized by 1H-NMR with the following chemical shifts: δ 2.27 (s, 3H), 2.46 (s, 3H), 2.50 (s, 3H), 7.27 (s, 1H), 7.55-7.62 (m, 2H), 7.85-7.89 (d, 2H).
