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.