Studien über die Thorpe‐Ziegler‐Reaktion Eine neue Synthese des Pyrimidinteils von Thiamin

Thorpe‐Ziegler cyclization of N′‐cyano‐N‐(2‐cyanoethyl)‐acetamidine (5a) yields 4‐amino‐2‐methyl‐1,6‐dihydro‐5‐pyrimidinecarbonitrile (8a). The acetamidine 5a is accessible either from the N‐cyanoimidate 1 and β‐aminopropionitrile (3a) or the N‐cyanoamidine 2 and acrylonitrile (4). The dihydropyrimidine 8a is easily converted to 4‐amino‐2‐methyl‐5‐pyrimidine‐carbonitrile (13) by dehydrogenation or to 4‐amino‐5‐aminomethyl‐2‐methylpyrimidine (15) by hydrogenation‐dehydrogenation. Both products are important intermediates in the synthesis of thiamine.