The general procedure for the synthesis of 2-amino-5-bromo-3-piperidinylpyrazine from hexahydropyridine and 2-amino-3,5-dibromopyrazine is as follows: hexahydropyridine (1.58 mmol) was added to 2-amino-3,5-dibromopyrazine (0.791 mmol) dissolved in DMSO or ethanol (0.5 ml), the mixture was placed in an airtight tube and the reaction was heated to 120°C for 18 hours. If the supply of hexahydropyridine is insufficient, one equivalent of hexahydropyridine and one equivalent of N,N-diisopropylethylamine (iPr2NEt) can be used as a base. After completion of the reaction, the reaction solution was cooled to room temperature and the organic phase was separated by partition extraction with dichloromethane and water (1:1, 200 mL). The aqueous phase was extracted once more with dichloromethane (50 mL), all organic layers were combined, dried over anhydrous sodium sulfate (Na2SO4) and concentrated under reduced pressure to give the target product 2-amino-5-bromo-3-piperidinylpyrazine. Prepared according to General Method 4 (Method 2) from the reaction of 2-amino-3,5-dibromopyrazine and piperidine to give diaminopyrazine (199 mg, 97% yield) as a yellow solid; 1H NMR (500 megahertz, CDCl3) δ 7.72 (single peak, 1H), 4.53 (single peak, 2H), 3.12-3.10 (triple peak, J=5.3 Hz, 4H) , 1.71-1.67 (multiple peaks, 4H), 1.65-1.61 (multiple peaks, 2H).
