N[C:2]1[S:3][C:4]2[CH2:5][N:6]([CH3:11])[CH2:7][CH2:8][C:9]=2[N:10]=1.N([O-])=O.[Na+].[OH-].[K+]>S(=O)(=O)(O)O.[PH2](O)=O.O>[CH3:11][N:6]1[CH2:7][CH2:8][C:9]2[N:10]=[CH:2][S:3][C:4]=2[CH2:5]1
2-Amino-5-methyl-4,5,6,7-tetrahydrothiazolo[5,4-c]pyridine (10.00 g) was dissolved in a mixture of sulfuric acid (25 mL), hypophosphorous acid (50%, 13 mL), and water (100 mL) at 15 to 18° C., to thereby give an orange solution. To the solution was added dropwise a solution of sodium nitrite (8.15 g) in water (30 mL) at −2 to 3° C. over 30 minutes. After the resultant mixture was stirred at 0 to 10° C. for 2.5 hours, 8N aqueous potassium hydroxide (130 mL) was added dropwise thereto, and the pH was found to be 12.6. The precipitated potassium sulfate was filtered off, and was washed with ethyl acetate (200 mL). The aqueous layer was separated from the filtrate, and was further extracted with ethyl acetate twice (200 mL×2). The organic layers were combined, and the combined organic layer was dried over sodium sulfate anhydrate (30.00 g). After any insoluble material was filtered off and washed with ethyl acetate (100 mL), the filtrate was concentrated under reduced pressure, to thereby give 6.15 g of the title compound.
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