9‐Hydroxy‐2‐methyl‐4H‐pyrido[1,2‐α] pyrimidin‐4‐one and its derivatives

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Abstract
2‐Amino‐3‐(o‐bromobenzyloxy)pyridine (1) and ethyl acetoacetate gave 9‐(o‐bromobenzyl‐oxy)‐2‐methyl‐4H‐pyrido[1,2‐α]pyrimidin‐4‐one (2) in 2% yield. When 1 and methyl β‐amino‐crotonate (3) were reacted, benzyl ether cleavage occurred and the products were 9‐hydroxy‐2‐methyl‐4H‐pyrido[1,2‐α]pyrimidin‐4‐one (4) and its ammonium salt (5). These observations led to an alternative synthesis in which 2‐amino‐3‐pyridinol (6) and either 3 or methyl acetoacetate, (8) in diethylbenzene at 185° gave 4 in 86 and 87% yields, respectively, and the anion of 4 and o‐bromobenzyl bromide gave 2 in 61% yield. Even in diethylbenzene at 185°, 1 and 8 gave only trace amounts of 2. Thus, o‐bromobenzylation of the 3‐hydroxyl group in 6 markedly decreased the reactivity of the amino group in 6 toward reactions with acetoacetic esters.

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